阅读说明：本技术 一种物料装车系统 (Material loading system ) 是由 杨松科 樊碧波 于 2019-09-05 设计创作，主要内容包括：本发明提供一种物料装车系统,包括：料库；底层出料装置,连接于所述料库底部；提升设备,连接于所述料库前部,所述提升设备包括底部进料口和顶部出料口,所述提升设备用于将所述底层出料装置输出的物料从所述底部进料口提升至顶部出料口；卸料装置,所述卸料装置包括进料口和卸料口,所述卸料装置的进料口与所述提升设备的顶部出料口连接；卸料装置支架,所述卸料装置支架用于承载所述卸料装置；装载道,所述装载道位于所述料库的前方,所述装载道包括入口和出口,用于承载货车,并导引所述货车至所述卸料装置的卸料口处。本发明能够极大幅度地提高卸料操作的灵活性和便利性。(The invention provides a material loading system, comprising: a material warehouse; the bottom layer discharging device is connected to the bottom of the material warehouse; the lifting equipment is connected to the front part of the material warehouse and comprises a bottom feeding hole and a top discharging hole, and the lifting equipment is used for lifting the material output by the bottom discharging device to the top discharging hole from the bottom feeding hole; the discharging device comprises a feeding hole and a discharging hole, and the feeding hole of the discharging device is connected with a discharging hole at the top of the lifting equipment; the discharging device bracket is used for bearing the discharging device; the loading channel is positioned in front of the material warehouse and comprises an inlet and an outlet, and the loading channel is used for bearing a truck and guiding the truck to a discharge port of the discharging device. The invention can greatly improve the flexibility and convenience of the unloading operation.)

1. A material loading system, comprising:

a material warehouse;

the bottom layer discharging device is connected to the bottom of the material warehouse and used for receiving the materials unloaded from the material warehouse and outputting the materials from the bottom of the material warehouse;

the lifting equipment is connected to the front part of the material warehouse and comprises a bottom feeding hole and a top discharging hole, and the lifting equipment is used for lifting the material output by the bottom discharging device to the top discharging hole from the bottom feeding hole;

the discharging device comprises a feeding hole and a discharging hole, and the feeding hole of the discharging device is connected with a discharging hole at the top of the lifting equipment;

the discharging device support is used for bearing the discharging device and enabling the discharging device to reciprocate on a track on the discharging device support;

the loading channel is positioned in front of the material warehouse and comprises an inlet and an outlet, and the loading channel is used for bearing a truck and guiding the truck to a discharge port of the discharging device.

2. The material handling system of claim 1,

the material storehouse comprises a gallery, the gallery is located at the bottom of the material storehouse, and the bottom layer discharging device is located in the gallery.

3. The material handling system of claim 2,

the bottom layer discharging device comprises a discharging port and a conveying rail, the discharging port is located above the conveying rail, and the conveying rail can receive discharging materials of the discharging port and output the materials from the bottom of the material warehouse along the conveying rail.

4. The material handling system of claim 1,

the lifting equipment comprises a bucket elevator or a belt conveyor, and the top discharge port at the upper part of the lifting equipment is positioned above the feed port of the discharging device.

5. The material handling system of claim 1,

the discharge device comprises a two-degree-of-freedom sealed discharge device, and the two-degree-of-freedom sealed discharge device comprises:

the conveying device comprises a first conveyor belt and a second conveyor belt, wherein the first conveyor belt comprises a first end and a second end opposite to the first end, the second end of the first conveyor belt is connected with the first end of the second conveyor belt through a first hinge, and the first conveyor belt and the second conveyor belt are used for conveying materials from the first end of the first conveyor belt to the second end of the second conveyor belt;

a belt dust cover located outside of and fixedly attached to the first and second belts, the belt dust cover including a first end and a second end opposite the first end, the first end of the belt dust cover being located at the first end of the first belt, the second end of the belt dust cover being located at the second end of the second belt;

the feeding hole is connected with the first end of the dust cover of the conveying belt and used for receiving materials to be conveyed to the first end of the first conveying belt;

the discharge opening is connected with the second end of the dust cover of the conveyor belt and is used for discharging the materials conveyed by the second conveyor belt;

the driving mechanism is connected with the conveyor belt dust cover and is used for driving the conveyor belt dust cover to move back and forth along a preset path;

and the lifting mechanism is connected with the second conveyor belt and the first conveyor belt and is used for driving the second conveyor belt to move up and down in the vertical direction around the first hinge.

6. The material loading system of claim 5,

the tripper bracket further comprises a base part, a support part and a suspension part:

the base is positioned at the bottom of the discharging device bracket and is used for enabling the discharging device bracket to be in contact with the ground;

the supporting part is fixedly connected with the base part and the hanging part and is used for supporting the hanging part on the base part;

a first track is formed on the hanger, the dust guard being slidably mounted on the first track such that the conveyor dust guard can move back and forth along the first track relative to the tripper bracket.

7. The material loading system of claim 6, wherein the hanging portion further comprises a hanging beam forming a vertical extension downwardly from the hanging portion, the first track being formed on the vertical extension; and a sliding part matched with the first track is formed on the dust cover, so that when the driving mechanism drives the first conveyor belt, the dust cover is driven to move back and forth relative to the discharging device support along the first track.

8. The material loading system of claim 1,

the loading passage further comprises:

an outer straight channel, a turntable channel, an inner straight channel and a loading channel;

the outer side straight road and the inner side straight road are both connected with the rotary table road, so that the truck can drive to the inner side straight road through the outer side straight road;

a loading channel is connected between the inner straight channel and the outer straight channel and is used for enabling the truck to receive unloading materials from the unloading device;

the loading channel comprises a first end and a second end opposite to the first end, the first end of the loading channel is connected to the inner side straight channel, and the second end of the loading channel is connected to the outer side straight channel and leads to an outlet of the loading channel on the outer side straight channel.

9. The material loading system of claim 8,

still include vehicle weighing device and automatic settlement device: the vehicle weighing device is positioned at the outlet and/or the inlet of the loading channel and is used for measuring the weight of the truck before and after loading; the automatic settlement device is positioned on one side of the vehicle weighing device and communicated with the vehicle weighing device, and is used for reading data of the vehicle weighing device, so that automatic settlement is realized.

10. The material loading system of claim 5,

also comprises a central control device which is used for controlling the central control device,

the central control device is connected with the two-degree-of-freedom sealed unloading device and used for controlling a transmission belt dust cover of the two-degree-of-freedom sealed unloading device to move back and forth along a preset path and controlling the second transmission belt to swing up and down in the vertical direction around the first hinge according to a target unloading position;

the central control device comprises:

a sensor module, a vehicle identification module, a stock pile state identification module, a two-degree-of-freedom sealed unloading device control module and a central processor, wherein,

the vehicle identification module, the material pile state identification module and the two-degree-of-freedom sealed unloading device control module are respectively connected with the central processing unit;

the sensor module is fixedly arranged at the head of the two-degree-of-freedom sealed unloading device and is respectively connected with the vehicle identification module and the material pile state identification module;

the two-degree-of-freedom sealed unloading device control module is respectively connected with the driving mechanism and the lifting mechanism and used for controlling the actions of the driving mechanism and the lifting mechanism.

Technical Field

The invention belongs to the field of material loading, and particularly relates to a material loading system.

Background

The crushed product is widely applied to industries such as metallurgy, building, coal, road building, chemical engineering and the like, plays an important role in the industrial production process, can be divided into different particle sizes according to the product application, and is often required to be loaded and transported for many times.

The traditional loading mode has the manual loading of loader, the loading of belt feeder, material jar blowing formula loading, and loader loading needs a shovel to dig to remove the back loading, and is inefficient, and the raise dust is many, extravagant manpower and material resources, and the cost is higher. The operation of ore field ore is more at present adopts the belt feeder transportation, transports the transport vechicle with the ore through the belt feeder on, but present belt feeder is mostly fixed knot structure, and freight train loading needs adjustment loading position many times just can be with the unloading end of freight train alignment belt, still need make a round trip to adjust very consuming time all around when unloading, and the blanking discrepancy in height is big, and the loading raise dust is big. Tank type feed bin storehouse bottom blowing also needs adjustment loading position many times, and tank type feed bin cost is high storehouse capacity volume and is little, to sum up, current loading system loading is inefficient, and the environment dust is big.

Disclosure of Invention

Accordingly, to overcome the above-mentioned disadvantages of the prior art, the present invention provides a material loading system to improve the flexibility and convenience of the unloading operation.

In order to achieve the above object, there is provided a material loading system including:

a material warehouse;

the bottom layer discharging device is connected to the bottom of the material warehouse and used for receiving the materials unloaded from the material warehouse and outputting the materials from the bottom of the material warehouse;

the lifting equipment is connected to the front part of the material warehouse and comprises a bottom feeding hole and a top discharging hole, and the lifting equipment is used for lifting the material output by the bottom discharging device to the top discharging hole from the bottom feeding hole;

the discharging device comprises a feeding hole and a discharging hole, and the feeding hole of the discharging device is connected with a discharging hole at the top of the lifting equipment;

the discharging device support is used for bearing the discharging device and enabling the discharging device to reciprocate on a track on the discharging device support;

the loading channel is positioned in front of the material warehouse and comprises an inlet and an outlet, and the loading channel is used for bearing a truck and guiding the truck to a discharge port of the discharging device.

Further, the silo includes a gallery located at the bottom of the silo, and the bottom outfeed device is located within the gallery.

Further, the bottom layer discharging device comprises a discharging port and a conveying rail, the discharging port is located above the conveying rail, and the conveying rail can receive discharging materials of the discharging port and output the materials from the bottom of the material warehouse along the conveying rail.

Further, the lifting equipment comprises a bucket elevator or a belt conveyor, and the top discharge port at the upper part of the lifting equipment is positioned above the feed port of the discharging device.

Further, the discharge device comprises a two-degree-of-freedom sealed discharge device, and the two-degree-of-freedom sealed discharge device comprises:

the conveying device comprises a first conveyor belt and a second conveyor belt, wherein the first conveyor belt comprises a first end and a second end opposite to the first end, the second end of the first conveyor belt is connected with the first end of the second conveyor belt through a first hinge, and the first conveyor belt and the second conveyor belt are used for conveying materials from the first end of the first conveyor belt to the second end of the second conveyor belt;

further, a belt dust cover located outside and fixedly connected to the first belt and the second belt, the belt dust cover including a first end and a second end opposite to the first end, the first end of the belt dust cover being located at the first end of the first belt, the second end of the belt dust cover being located at the second end of the second belt;

the feeding hole is connected with the first end of the dust cover of the conveying belt and used for receiving materials to be conveyed to the first end of the first conveying belt;

the discharge opening is connected with the second end of the dust cover of the conveyor belt and is used for discharging the materials conveyed by the second conveyor belt;

the driving mechanism is connected with the conveyor belt dust cover and is used for driving the conveyor belt dust cover to move back and forth along a preset path;

and the lifting mechanism is connected with the second conveyor belt and the first conveyor belt and is used for driving the second conveyor belt to move up and down in the vertical direction around the first hinge.

Further, the tripper bracket further comprises a base, a support and a suspension:

the base is positioned at the bottom of the discharging device bracket and is used for enabling the discharging device bracket to be in contact with the ground;

the supporting part is fixedly connected with the base part and the hanging part and is used for supporting the hanging part on the base part;

a first track is formed on the hanger, the dust guard being slidably mounted on the first track such that the conveyor dust guard can move back and forth along the first track relative to the tripper bracket.

Further, the hanging portion further includes a hanging beam forming a vertical extension downward from the hanging portion, the first rail being formed on the vertical extension; and a sliding part matched with the first track is formed on the dust cover, so that when the driving mechanism drives the first conveyor belt, the dust cover is driven to move back and forth relative to the discharging device support along the first track.

Further, the loading passage further comprises:

an outer straight channel, a turntable channel, an inner straight channel and a loading channel;

the outer side straight road and the inner side straight road are both connected with the rotary table road, so that the truck can drive to the inner side straight road through the outer side straight road;

a loading channel is connected between the inner straight channel and the outer straight channel and is used for enabling the truck to receive unloading materials from the unloading device;

the loading channel comprises a first end and a second end opposite to the first end, the first end of the loading channel is connected to the inner side straight channel, and the second end of the loading channel is connected to the outer side straight channel and leads to an outlet of the loading channel on the outer side straight channel.

Further, the vehicle weighing device and the automatic settlement device are also included: the vehicle weighing device is positioned at the outlet and/or the inlet of the loading channel and is used for measuring the weight of the truck before and after loading; the automatic settlement device is positioned on one side of the vehicle weighing device and communicated with the vehicle weighing device, and is used for reading data of the vehicle weighing device, so that automatic settlement is realized.

Furthermore, the device also comprises a central control device,

the central control device is connected with the two-degree-of-freedom sealed unloading device and used for controlling a transmission belt dust cover of the two-degree-of-freedom sealed unloading device to move back and forth along a preset path and controlling the second transmission belt to swing up and down in the vertical direction around the first hinge according to a target unloading position;

the central control device comprises:

a sensor module, a vehicle identification module, a stock pile state identification module, a two-degree-of-freedom sealed unloading device control module and a central processor, wherein,

the vehicle identification module, the material pile state identification module and the two-degree-of-freedom sealed unloading device control module are respectively connected with the central processing unit;

the sensor module is fixedly arranged at the head of the two-degree-of-freedom sealed unloading device and is respectively connected with the vehicle identification module and the material pile state identification module;

the two-degree-of-freedom sealed unloading device control module is respectively connected with the driving mechanism and the lifting mechanism and used for controlling the actions of the driving mechanism and the lifting mechanism.

Compared with the prior art, the material loading system can ensure that trucks can enter and exit a stock yard in order without mutual interference, and saves the space of the yard. After the position of the truck is determined, two-degree-of-freedom sealed unloading is carried out, continuous unloading in different directions can be achieved, accurate unloading of a blanking point is achieved through the detection device, the degree of automation is high, time waste caused by the fact that the truck is aligned with the discharging end of the belt is avoided, and the loading and unloading efficiency is obviously improved. The dust-free belt conveyor can stretch into the carriage, so that the blanking point is reduced, a continuous stacking mode is formed, the dust is reduced, the environmental pollution is reduced, and the loading and unloading efficiency is obviously improved.

Drawings

FIG. 1 is a top view of one embodiment of a material loading system of the present invention.

Fig. 2 is a schematic structural view in the direction of a-a in fig. 1.

Fig. 3 is a front view of a two-degree-of-freedom sealed discharge device in an embodiment of the material loading system of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to specific embodiments and the accompanying drawings.

In one embodiment of the present invention, as shown in fig. 1-3, there is provided a material loading system comprising:

a material warehouse 1;

the bottom layer discharging device 2 is connected to the bottom of the material warehouse 1 and used for receiving the materials unloaded from the material warehouse 1 and outputting the materials from the bottom of the material warehouse 1;

the lifting equipment 3 is connected to the front part of the material warehouse 1, the lifting equipment 3 comprises a bottom feeding hole and a top discharging hole, and the lifting equipment 3 is used for lifting the material output by the bottom layer discharging device 2 from the bottom feeding hole to the top discharging hole;

the discharging device 4 comprises a feeding hole and a discharging hole, and the feeding hole of the discharging device 4 is connected with the discharging hole at the top of the lifting device 3;

a discharging device bracket 5, wherein the discharging device bracket 5 is used for bearing the discharging device 4 and enabling the discharging device 4 to reciprocate on a track 55 on the discharging device bracket 5;

a loading channel 6, said loading channel 6 being located in front of said magazine 1, said loading channel 6 comprising an inlet and an outlet for carrying a truck and guiding said truck to a discharge opening of said discharge device 4.

In one embodiment, to facilitate tapping, the silo 1 comprises a gallery 11, the gallery 11 being located at the bottom of the silo 1, the bottom tapping device 2 being located within the gallery 11.

In one embodiment, the silo 1 is divided into different material areas according to different materials and sizes of different materials, and a gallery 11 is arranged below each area.

In one embodiment, the bottom layer discharging device 2 comprises a discharge port and a conveying track, wherein the discharge port is positioned above the conveying track, and the conveying track can receive the discharging material of the discharge port and output the material from the bottom of the material warehouse along the conveying track.

In one embodiment, the bottom layer discharging device 2 further comprises a feeding machine, which is positioned at the discharging port to facilitate the discharging of the discharging port.

In one embodiment, the lifting device 3 comprises a bucket elevator or a belt conveyor, the top discharge opening of which is located above the feed opening of the discharge device 4.

In one embodiment, the discharge device 4 comprises: the sealed discharge apparatus of two degrees of freedom, this sealed discharge apparatus of two degrees of freedom includes:

a first conveyor belt 41 and a second conveyor belt 42, wherein the first conveyor belt 41 comprises a first end and a second end opposite to the first end, the second conveyor belt 42 comprises a first end and a second end opposite to the first end, the second end of the first conveyor belt 41 is connected with the first end of the second conveyor belt 42 through a first hinge, and the first conveyor belt 41 and the second conveyor belt 42 are used for conveying materials from the first end of the first conveyor belt 41 to the second end of the second conveyor belt 42;

in one embodiment, the two-degree-of-freedom sealed unloading device comprises a belt dust cover 43, the belt dust cover 43 is located at the outer side of the first belt 41 and the second belt 42 and is fixedly connected with the first belt 41 and the second belt 42, the belt dust cover 43 comprises a first end and a second end opposite to the first end, the first end of the belt dust cover 43 is located at the first end of the first belt 41, and the second end of the belt dust cover 43 is located at the second end of the second belt 42;

the feed inlet is connected with the first end of the conveyor belt dust cover 43 for receiving the material to be conveyed to the first end of the first conveyor belt 41;

said discharge opening being connected to a second end of said belt shield 43 for discharging material conveyed from said second conveyor belt 42;

a drive mechanism 44, wherein the drive mechanism 44 is connected with the belt dust covers 43 for driving the belt dust covers 43 to move back and forth along a predetermined path;

and the lifting mechanism 45 is connected with the second conveyor belt 42 and the first conveyor belt 41, and is used for driving the second conveyor belt 42 to move up and down in the vertical direction around the first hinge.

When the target material discharging position is determined, the material enters the first conveyor belt of the two-degree-of-freedom sealed discharging device from the feed inlet at the first end of the conveyor belt dust cover, the control system controls the lifting mechanism of the driving mechanism 6 to act cooperatively, the discharge point of the discharge belt conveyor is adjusted horizontally and vertically according to the position of the truck or the discharge point, the driving mechanism controls the dust cover of the conveyor belt to walk, the lifting mechanism controls the second conveyor belt to swing up and down, the two processes can be carried out simultaneously, the continuous discharging in different directions can be realized, meanwhile, the dust cover of the driving belt can greatly reduce the dust pollution caused in the charging and discharging process, therefore, full automation can be realized, accurate unloading is realized, dust is reduced, the waste of time caused by aligning the truck with the lower discharging end of the belt is avoided, and the loading and unloading efficiency is obviously improved.

In one embodiment, to improve the working efficiency, and the reliability of the discharge, in one embodiment, a discharge device support 5 is provided, said discharge device support 5 further comprising a base portion 51, a support portion 52 and a hanging portion 53:

the base 51 is positioned at the bottom of the discharge device support 5 and is used for contacting the discharge device support 5 with the ground;

the supporting portion 52 is fixedly connected with the base portion 51 and the hanging portion 53, and is used for supporting the hanging portion 53 on the base portion 51;

a first track is formed on the suspension 53 on which the dust guard is slidably mounted so that the conveyor dust guard 43 can move back and forth along the first track relative to the tripper device frame 5.

In one embodiment, the hanging portion 53 further comprises a hanging beam 531, the hanging beam 531 forming a vertical extension downward from the hanging portion 53, the first track being formed on the vertical extension; a sliding portion matched with the first rail is formed on the dust cover, so that when the driving mechanism 44 drives the first conveyor belt 41, the dust cover is driven to move back and forth along the first rail relative to the discharging device bracket 5.

In one embodiment, to facilitate accurate control of the discharge, a belt scale 46 is included, which is fixedly mounted on the two-degree-of-freedom sealed discharge device, for weighing the material actually loaded by each truck.

In one embodiment, the loading chute 6 is configured in a particular shape, including:

an outer straight channel 61, a rotary channel 62, an inner straight channel 63 and a charging channel 64;

wherein the outer straight road 61 and the inner straight road 63 are both connected with the rotary table road 62, so that the truck can drive to the inner straight road 63 through the outer straight road 61; when the turning radius of the rotary table way 62 is set, the truck can normally pass through.

A loading channel 6 is connected between the inner straight channel 63 and the outer straight channel 61, and the loading channel 6 is used for enabling the truck to receive the unloading material from the unloading device 4;

the loading channel 6 comprises a first end and a second end opposite to the first end, the first end of the loading channel 6 is connected to the inner straight channel 63, and the second end of the loading channel 6 is connected to the outer straight channel 61 and leads to an outlet of the loading channel 6 on the outer straight channel 61.

In one embodiment, it also comprises a vehicle weighing device 7 and an automatic settlement device 8: the vehicle weighing device 7 is positioned at the outlet and/or inlet of the loading channel 6 and is used for measuring the weight of the truck before and after loading; the automatic settlement device 8 is positioned on one side of the vehicle weighing device 7 and communicated with the vehicle weighing device 7 and used for reading data of the vehicle weighing device 7, so that automatic settlement is realized.

In order to improve the efficiency of automatic discharging, in one embodiment, the automatic discharging device further comprises a central control device,

the central control device is connected with the two-degree-of-freedom sealed unloading device and used for controlling a transmission belt dust cover of the two-degree-of-freedom sealed unloading device to move back and forth along a preset path and controlling the second transmission belt 42 to swing up and down in the vertical direction around the first hinge according to a target unloading position;

the central control device comprises:

a sensor module 91, a vehicle identification module 92, a stock pile state identification module, a two-degree-of-freedom sealed unloading device control module and a central processor, wherein,

the vehicle identification module 92, the stock pile state identification module 93 and the two-degree-of-freedom sealed unloading device control module are respectively connected with the central processing unit;

the sensor module 91 is fixedly installed at the head of the two-degree-of-freedom sealed unloading device and is respectively connected with the vehicle identification module 92 and the material pile state identification module;

the two-degree-of-freedom sealed unloading device control module is respectively connected with the driving mechanism 44 and the lifting mechanism 45 and is used for controlling the actions of the driving mechanism 44 and the lifting mechanism 45.

The mode of operation of the invention is described below.

The material loading system of the present invention operates as follows:

the truck passes through the outer side straight channel and the rotary table channel and then enters the inner side straight channel, and finally enters the corresponding loading channel according to the required loading materials.

When the truck is in place, starting the automatic loading system, controlling the first and second conveyor belts to move to the position of the truck by the central control system after the truck is stopped in the loading area, identifying the length, the width and the height of the truck through the sensor module, and transmitting information to the central control system;

the central control system controls the first conveyor belt and the second conveyor belt to move, so that the dustproof funnel loaded on the head of the second conveyor belt moves to the head of the carriage;

the position of a discharge opening of the second conveyor belt is adjusted by utilizing the extension and contraction of the lifting mechanism, so that the sliding funnel is arranged at a proper position at the bottom of the carriage, and the lower edge of the sliding funnel is completely sealed with the bottom of the carriage;

starting the first conveyor belt and the second conveyor belt for discharging, and simultaneously driving the second conveyor belt to rotate by using the lifting mechanism to enable the blanking point to slowly move upwards for discharging, wherein the lower edge of the sliding hopper is always in contact with the material in the process, so that the raised dust is reduced;

the material height in the vehicle is identified through the material state identification module, information is transmitted to the central control system, the lifting mechanism stops working until the material height reaches a set height, the central control system controls the first conveyor belt and the second conveyor belt to slowly move backwards along the carriage for discharging until the head of the second conveyor belt moves to the tail of the carriage and fills the carriage, and the second conveyor belt stops working. .

This mode is once only piled up the material in vertical direction, then utilizes drive arrangement in proper order to the continuous windrow of carriage afterbody, and the dust cover of rotatory belt head contacts the material all the time, forms airtight space, reduces the raise dust, accomplishes the loading under the unmovable condition of vehicle, improves loading efficiency.

After loading is finished, the truck travels to an outer lane along the loading channel and enters an outlet channel, and the weight of the truck before and after loading is measured by the vehicle weighing device; the automatic settlement device is used for reading data of the vehicle weighing device according to the measuring signal of the vehicle weighing device, so that automatic settlement is realized.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention. The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.