Differential Global Positioning System and Positioning Method Thereof

[0001] The present invention relates to the field of accurate positioning, and in particular to a differential global positioning system in a certain area, and a positioning method of the differential global positioning system.

[0002] With the development of technologies for global positioning systems (GPS, Beidou, and the like), in order to achieve more accurate positioning, more and more people use a differential global positioning system (DGPS) to implement accurate positioning of moving objects.

[0003] The differential global positioning system (DGPS) implements observation by using a GPS receiver disposed on a base station. Based on the known precision coordinates of the base station, the deviation correction data from the base station to the satellite is calculated, and the data is transmitted by the base station in real time. A user receiver also receives the correction data sent by the base station while performing GPS observation, and corrects a positioning result to improve the positioning accuracy.

[0004] There are currently two manners to apply the differential global positioning system (DGPS) on a machine. One is to use a self-built base station, which transmits differential correction data to correct measurement errors for high-accuracy positioning. However, in this way, for an individual user, a machine needs an independent base station, so the cost is too high, and each base station uses large space. Another manner is to use Continuously Operating Reference Stations (CORS) to achieve high-accuracy positioning based on data transmission between a machine and a CORS base station. However, for an individual user, CORS signals transmitted by the CORS base station are a paid service requiring additional fee, so the usage cost is high.

[0005] One aspect of an embodiment of the invention features a differential global positioning system, comprising a base station and at least one intelligent device, wherein the base station is configured to set first positioning data thereof when the base station is arranged at a fixed location, and the base station comprises a first signal receiver; wherein the first signal receiver receives satellite-based positioning signals sent by a satellite system to obtain second positioning data of the base station, and the base station obtains differential correction data according to a measurement error between the first positioning data and the second positioning data, and the base station is in communication connection with at least two intelligent devices to transmit the corresponding differential correction data to the at least two intelligent devices.

[0006] In one embodiment, the at least one intelligent device comprises an encoding module for encoding the corresponding intelligent device to obtain codes; and the base station determines whether to transmit the differential correction data to the corresponding intelligent device according to whether the codes match preset data information of the base station.

[0007] In one embodiment, the base station comprises a sending module for sending the differential correction data to the intelligent device, and a control module for storing the codes of the intelligent device, and controlling whether the sending module sends the differential correction data to the intelligent device according to the codes provided by the intelligent device.

[0008] In one embodiment, the differential global positioning system comprises at least two transmission paths for transmitting the corresponding differential correction data to the corresponding intelligent devices; wherein when the base station receives a request instruction sent by a corresponding intelligent device for obtaining the differential correction data, the base station instructs the corresponding intelligent device to obtain the corresponding differential correction data through a corresponding transmission path.

[0009] In one embodiment, each intelligent device comprises a shell and a mobile station connected to the shell, and the base station is in communication connection with the intelligent device via the mobile station.

[0010] In one embodiment, each intelligent device comprises a second signal receiver and a third signal receiver disposed separately; the second signal receiver receives satellite-based positioning signals sent by a satellite-based positioning system to obtain positioning data of the corresponding intelligent device at a current location, and the third signal receiver is configured to receive the differential correction data sent by the base station; and the second signal receiver and the third signal receiver are integrated on the mobile station of each intelligent device.

[0011] In one embodiment, the intelligent device is a self-moving device or an intelligent robot.

[0012] In one embodiment, the intelligent device comprises an inertial navigation system.

[0013] In one embodiment, a distance between the intelligent device and the satellite-based positioning system is equal to a distance between the base station and the satellite-based positioning system.

[0014] In one embodiment, an angle formed by a line connecting the base station and the satellite-based positioning system and a line connecting the intelligent device and the satellite-based positioning system is less than or equal to 0.3 degree.

[0015] The differential global positioning system can accurately locate an intelligent device. A base station can establish communications with multiple intelligent devices, so the differential global positioning system is expandable, and can connect to multiple intelligent devices or have multiple intelligent devices added thereto according to actual conditions. This is equivalent to setting up a regional differential global positioning network, thereby eliminating the need to establish a base station for each intelligent device and greatly saving costs. The number of intelligent devices may be added or reduced as needed, and a coverage of the base station can be adjusted to make the differential positioning more flexible and convenient.

[0016] A differential global positioning system, comprising a base station, wherein the base station is configured to set first positioning data thereof when the base station is arranged at a fixed location, and the base station comprises a first signal receiver; wherein the first signal receiver receives satellite-based positioning signals sent by a satellite-based positioning system to obtain second positioning data of the base station, and the base station obtains differential correction data according to a measurement error between the first positioning data and the second positioning data, and the base station is in communication connection with at least two intelligent devices to transmit the corresponding differential correction data to the at least two intelligent devices.

[0017] In one embodiment, the at least one of the at least two intelligent devices comprises an encoding module for encoding the corresponding intelligent device to obtain codes; and the base station determines whether to transmit the differential correction data to the corresponding intelligent device according to whether the code matches preset data information of the base station.

[0018] In one embodiment, the differential global positioning system comprises at least two transmission paths for transmitting the corresponding differential correction data to the corresponding intelligent devices; wherein when the base station receives a request instruction sent by the corresponding intelligent devices for obtaining the differential correction data, the base station instructs the at least two intelligent devices to obtain the corresponding differential correction data through different transmission paths.

[0019] In one embodiment, each intelligent device comprises a shell and a mobile station connected to the shell, and the base station is in communication connection with the intelligent device via the mobile station.

[0020] In one embodiment, the intelligent device is a self-moving device or an intelligent robot.

[0021] A positioning method of a differential global positioning system, the differential global positioning system comprising a base station, wherein the base station is configured to set first positioning data thereof when the base station is located at a fixed location, and the base station is in communication connection with at least one intelligent device; the base station further comprises an analysis module, and each intelligent device comprises a processing module, wherein the positioning method comprises at least following steps:

[0022] Step 1: data acquisition: obtaining second positioning data of the base station according to satellite-based positioning signals sent by a satellite-based positioning system, and transmitting the first positioning data and the second positioning data to the analysis module of the base station; and

[0023] Step 2: data analysis: receiving and analyzing, by the analysis module of the base station, the first positioning data and the second positioning data in the step 1 to obtain differential correction data of the base station, and transmitting the obtained differential correction data to the processing module of the at least one intelligent device.

[0024] In one embodiment, the positioning method of a differential global positioning system further comprising step 3: data processing: receiving, by the processing module of the intelligent device, the differential correction data, and correcting, according to the differential correction data, positioning data of the corresponding intelligent device at a current location obtained by the corresponding intelligent device by receiving the satellite-based positioning signals.

[0025] In one embodiment, the intelligent device further comprises an instruction module, and the positioning method further comprises step 4: instruction issuing: feeding back the positioning data corrected by the intelligent device to the instruction module, and controlling, by the instruction module, a moving path of the intelligent device, and sending out an execution instruction.

[0026] In one embodiment, the intelligent device further comprises an execution module, and the positioning method further comprises step 5: instruction execution: receiving, by the execution module, the instruction issued by the instruction module, and triggering the intelligent device to travel according to the obtained moving path.

[0027] In one embodiment, the at least one intelligent device comprises an encoding module, and the encoding module is configured to encode the corresponding intelligent device to obtain a code; and the step 2 further comprises: when the analysis module of the base station obtains the differential correction data of the base station through analysis, determining, by the base station, whether to transmit the differential correction data to the corresponding intelligent device according to whether the code matches preset data information of the base station.

[0028] In one embodiment, the base station comprises a sending module for sending the differential correction data to the intelligent device, and a control module for storing the code of the intelligent device, and controlling whether the sending module sends the differential correction data to the intelligent device according to the code provided by the intelligent device.

[0029] In one embodiment, the differential global positioning system comprises at least two transmission paths for transmitting the differential correction data to the corresponding intelligent devices, and between the step 2 and the step 3, the method further comprises: sending, by the corresponding intelligent device, an instruction to the base station to request for the differential correction data, and receiving, by the base station, the instruction, and instructing the corresponding intelligent device to obtain the corresponding differential correction data through a corresponding transmission path.

[0030] In one embodiment, the number of the transmission paths is less than or equal to the number of the intelligent devices.

[0031] In one embodiment, the intelligent device comprises a shell and a mobile station connected to the shell, and the base station is in communication connection with the intelligent device via the mobile station.

[0032] In one embodiment, the processing module, the instruction module, and the execution module of the intelligent device are integrated on a mobile station of each intelligent device.

[0033] In one embodiment, the second positioning data changes with the time of the satellite-based positioning signals transmitted by the satellite-based positioning system.

[0034] In one embodiment, the positioning data obtained by the intelligent device by receiving the satellite-based positioning signals sent by the satellite-based positioning system changes with the time when the positioning signals are transmitted by the satellite-based positioning system.

[0035] In the positioning method of a differential global positioning system, a base station can implement positioning of multiple intelligent devices, thereby greatly reducing the cost for positioning the intelligent devices.

[0039] In order to make the objectives, features, and advantages of the present invention more obvious and comprehensible, embodiments of the present invention are described in detail below with reference to the drawings.

[0040] FIG. 1 is a schematic diagram illustrating the structure of a differential global positioning system according to an embodiment of the present invention. As shown in FIG. 1, a differential global positioning system 100 includes a base station 110. Certainly in this embodiment, the differential global positioning system further includes at least one intelligent device. The base station 110 is in communication connection with at least one intelligent device. Specifically, the intelligent device may be a self-moving device 200 in some embodiments. Certainly in other embodiments, the self-moving device may also be an intelligent robot or the like. The self-moving device 200 and the base station 110 may receive satellite-based positioning signals from a satellite-based positioning system to achieve positioning. In this embodiment, a satellite-based positioning system is a GPS satellite 300, and the base station 110 and the self-moving device 200 receive the GPS positioning signals from the satellite-based positioning system to implement the GPS positioning. Certainly the satellite-based positioning system may also be a Galileo satellite navigation system, a Beidou satellite navigation system, or GLONASS.

[0041] The base station 110 transmits differential correction information to the self-moving device 200 to implement differential satellite-based positioning. Specifically, the base station 110 is configured to have a fixed accurate position when the base station is arranged at a fixed location, and the location is defined as first positioning data of the base station 110. In this embodiment, the first positioning data is represented by coordinate values, specifically (x1, y1). The base station 110 includes a first signal receiver (not shown), and the first signal receiver receives the satellite-based positioning signals sent by the satellite-based positioning system to obtain second positioning data of the base station 110. In this embodiment, the second positioning data is represented by coordinate values, specifically (x2, y2). Herein, the first signal receiver is a GPS signal receiver. Differential correction data e may be obtained according to a measurement error between the first positioning data (x1, y1) and the second positioning data (x2, y2). The base station 110 may be in communication connection with at least two self-moving devices 200 to transmit the corresponding differential correction data e to the at least two self-moving devices 200. It should be noted that generally the second positioning data obtained by the base station 110 according to the received GPS positioning signals sent by the satellite-based positioning system is a variable, which changes with the time when the GPS positioning signals are transmitted by the satellite-based positioning system, so that during the operation of the self-moving devices, the base station continuously transmits the differential correction data e to the self-moving devices 200, and the self-moving devices correct positioning data that is obtained by the satellite-based positioning system by receiving the GPS-based positioning signals in real time according to the obtained differential correction data.

[0042] Each self-moving device 200 includes a second signal receiver (not shown) and a third signal receiver (not shown) disposed separately, where the second signal receiver is configured to receive the GPS positioning signals from the satellite-based positioning system to obtain the positioning data of the corresponding self-moving device 200, and the third signal receiver is configured to receive the differential correction data sent by the base station 110. The self-moving device 200 further includes a shell (not labeled) and a mobile station 120 connected to the shell, and the base station 110 establishes a communication connection with the self-moving device 200 via the mobile station 120. The second signal transmitter and the third signal transmitter are integrated on the mobile station 120 of each self-moving device 200. In this embodiment, the mobile station 120 is detachably connected with the self-moving device 200. The mobile station 120 is accommodated in the shell, and when the mobile station 120 is installed in the shell of the self-moving device 200, the positioning data of the self-moving device 200 at a current location may be output according to the received GPS positioning signals. Certainly in other embodiments, the mobile station 120 may also be located outside the shell of the self-moving device 200, and a user can move the corresponding mobile station 120 to a specific location to obtain location data at the specific location.

[0043] The differential global positioning system 100 needs to establish only one base station 110, and communicates the at least two self-moving devices 200 by using the base station 110 to achieve accurate positioning of the self-moving devices 200. The base station 110 can establish communications with multiple self-moving devices 200, so the differential global positioning system 100 is expandable, and can connect to multiple self-moving devices 200 or have multiple self-moving devices 200 added thereto according to actual conditions. This is equivalent to setting up a regional differential global positioning network, thereby eliminating the need to establish the base station 110 for each self-moving devices 200 and greatly saving costs. The number of self-moving devices 200 can be increased or reduced as needed, and the coverage of the base station 110 can be adjusted to make the differential positioning more flexible and convenient.

[0044] In an embodiment, transmission of differential correction data information between the base station 110 and the self-moving device 200 may not need additional operation procedures. As long as the base station 110 exists and the self-moving device 200 is set within the coverage of the base station 110, the mobile station 120 on the self-moving device 200 receives the differential correction data in real time or within a preset time period, and corrects positioning data obtained by the corresponding self-moving device 200 by receiving the GPS positioning signals according to the corresponding differential correction data to ensure accurate positioning of the current location of the corresponding self-moving device in real time or within a preset time period. The following is a schematic illustration of the embodiment. The corresponding differential correction data obtained by the base station 110 may be understood as being transmitted to the outside in the form of a radio message or broadcast. Within the coverage of the base station 110, the self-moving device 200 receives the differential correction data sent by the base station 110 in real time or within a preset period of time without an intermediate program, and corrects the positioning data of the self-moving device 200 at the current location according to the received differential correction data.

[0045] In an embodiment, a communication connection between at least one of the at least two mobile devices 200 and the base station 110 may include a secret key process. Specifically, as shown in FIG. 1, at least one self-moving device 200 includes an encoding module 111 for encoding the corresponding self-moving device 200 to obtain a code, and the base station 110 determines whether to transmit the differential correction data to the self-moving device 200 according to whether the code matches preset data information of the base station 110. Further, the base station 110 includes a sending module 113 and a control module 114. The sending module 113 is configured to send the differential correction data to the self-moving device 200, and the control module 114 is configured to store the code of the self-moving device, and control whether the sending module sends the differential correction data to the self-moving device 200 according to the code provided by the self-moving device 200. In this embodiment, the encoding module of the self-moving device 200 is disposed on the mobile station 120. Certainly in other embodiments, the encoding module and the mobile station 120 may also be disposed independently on the self-moving device 200. The following is an illustration of this embodiment. For example, there exist two self-moving devices 200, and both self-moving devices 200 have a mobile station. Specifically one self-moving device has a mobile station 120a, and the other self-moving device has a mobile station 120b. The base station 110 determines whether to establish communication with the mobile stations 120a and 120b according to whether the code of the mobile stations 120 is correct. When the code of the mobile station 120a received by the base station 110 is correct, the differential correction data is transmitted to the mobile station 120a; otherwise, the mobile station 120a may not obtain the corresponding differential correction data or obtain a wrong messy code. Similarly when the code of the mobile station 120b received by the base station 110 is correct, the differential correction data is transmitted to the mobile station 120b; otherwise, the mobile station 120b may not obtain the corresponding differential correction data or obtain a wrong messy code.

[0046] In an embodiment, the code of the mobile stations 120 within the coverage of the same base station 110 is uniquely identified so as to ensure the security and reliability of the established communication.

[0047] In an embodiment, the differential global positioning system 100 includes at least two transmission paths for transmitting corresponding differential correction data to corresponding self-moving devices 200. The number of the transmission paths is less than or equal to the number of the self-moving devices 200. When the base station 110 receives a request instruction sent by a corresponding self-moving device 200 for obtaining the differential correction data, the base station 110 instructs the self-moving device 200 to obtain the corresponding differential correction data through a corresponding transmission path. Further, when at least two self-moving devices 200 need to obtain differential correction data, and the format of the differential correction data to be obtained by the at least two self-moving devices 200 is the same, the base station 110 receives request instructions sent by the corresponding self-moving devices 200 for obtaining the differential correction data, and instructs the at least two self-moving devices 200 to obtain the corresponding differential correction data through any transmission path. When at least two self-moving devices 200 need to obtain differential correction data, and the formats of the differential correction data to be obtained by the at least two self-moving devices 200 are different, the base station 110 instructs the at least two self-moving devices 200 to obtain the corresponding differential correction data through different transmission paths. Further, the base station 110 also includes an identification module. When a self-moving device 200 sends a request instruction for obtaining differential correction data to the base station 110, the base station 110 determines whether the self-moving device satisfies a condition for receiving the differential correction data. Specifically, the condition may be whether the self-moving device 200 and the base station 110 have reached a differential data transmission license agreement. If the identification module determines that the self-moving device 200 has a differential data transmission permission from the base station 110, the base station 110 may successfully send the corresponding differential correction data to the self-moving device 200; if the identification module determines that the self-moving device 200 does not have the differential data transmission permission from the base station 110, the base station 110 cannot successfully send the corresponding differential correction data to the self-moving device 200, that is, the transmission path is automatically cut off. The following is a schematic illustration of this embodiment. The corresponding differential correction data obtained by the base station 110 may be understood as being transmitted to the outside in the form of a radio message or broadcast, and the at least two transmission paths may be understood as different frequency bands. When multiple self-moving devices 200 send requests for obtaining the corresponding differential correction data to the base station 110, the base station 110 receives the requests, and informs the corresponding self-moving devices 200 of the transmission paths at certain frequency bands through which the self-moving devices 200 can obtain the differential correction data.

[0048] In the differential global positioning system 100 in this design, the base station may define different receiving formats for different self-moving devices 200, and cut off the transmission paths of the self-moving devices 200 that do not have the permission in time. At the same time, other self-moving devices 200 with the permission can normally receive the differential correction data information. Therefore, this embodiment ensures that the self-moving devices of different models and different specifications can successfully receive the correct differential correction data. In another aspect, the base station 110 ensures the security of the data transmission between the base station 110 and the self-moving devices 200 by setting up a plurality of transmission paths; even if the transmission of a certain path is cut off, no interference is caused to other transmission paths, so that the base station 110 achieves more secure management.

[0049] In an embodiment, the self-moving device 200 is an intelligent lawn mower. Each intelligent lawn mower has a mobile station 120. Each intelligent lawn mower has an independent working area. For example, a base station 110 is established in a community, and each household has a self-moving device. In an embodiment, the self-moving devices are intelligent robots or intelligent power devices, such as intelligent weeders and intelligent lawn mowers. The self-moving device of each household in the community may establish communication with the base station 110, thereby achieving differential global positioning. In this way, the positioning of the self-moving devices in the area is effectively achieved, and the cost is greatly reduced.

[0050] In one embodiment, as shown in FIG. 1, the base station 110 further includes a receiving antenna 112 for receiving the GPS positioning signals, a sending module 113 for transmitting the differential correction data to the mobile stations 120, and a control module 114 for calculating the differential correction data, storing the code of the plurality of mobile stations 120, and controlling the sending module 113 to send the differential correction data to the different mobile stations 120 according to the code. In an embodiment, the coverage of the base station is within a radius of 50 kilometers to ensure accurate positioning of each intelligent device.

[0051] In an embodiment, the number of the intelligent devices (e.g. 200) arranged in the coverage of the base station 110 is not more than 1000, so as to prevent or reduce communication congestion caused by an excessive number of intelligent devices within the coverage of the base station 110, thereby ensuring operational stability of the base station 110 and the positioning accuracy of each self-moving device (e.g. 200).

[0052] FIG. 2 is a schematic diagram illustrating the structure of a self-moving device equipped with a differential global positioning system according to an embodiment of the present invention. A self-moving device 200 is provided with a mobile station 120, and the self-moving device 200 further includes a receiving antenna 210 for receiving a GPS positioning signals, where the GPS positioning signals are global satellite-based positioning signal, such as GPS, Beidou or Galileo, and the like for obtaining global positioning information. In addition, the mobile station 120 further includes a communication module 122 and a processing module 121. The communication module 122 is configured to establish communication with the base station 110 to receive differential correction data, and the processing module 121 is connected to the receiving antenna 210 and the communication module 122 for processing the received GPS positioning signals and differential correction data for implementing high-accuracy positioning. In the differential global positioning system, one base station 110 can implement positioning of multiple self-moving devices, thereby greatly reducing the cost of positioning the self-moving devices.

[0053] In an embodiment, the self-moving device 200 further includes an inertial navigation system for outputting accurate positioning data for navigation when there are obstacles and satellite signals are not good. The inertial navigation system measures an acceleration and angular velocity of the self-moving device 200, integrates over time the acceleration, and transforms the acceleration to the navigation coordinate system to obtain the information of the velocity, yaw angle, location. Therefore, in mountain areas or forest areas with poor communication signals and unfavorable conditions, the inertial navigation system may be used for accurate positioning for the self-moving device 200 to make the differential global positioning system more applicable and more accurate.

[0054] It can be further understood that the self-moving device 200 may be an intelligent lawn mower, an intelligent lawn trimmer, and an intelligent weeder, but is not limited to the listed machines.

[0055] FIG. 3 is a schematic diagram illustrating the operation of the differential global positioning system. As shown in FIG. 3, the base station 110 and the self-moving devices 200 receive GPS positioning signals from the GPS satellite 300 to determine the locations of GPS positioning. The base station 110 calculates differential correction data e according to a measurement error between the accurate position thereof and the location of the GPS positioning, and transmits the differential correction data e to the self-moving devices 200. The self-moving device 200 calculate the accurate positioning locations thereof according to the received GPS satellite signals and the received differential correction data e. Normally, an angle a at the GPS satellite between the base station 110 and the self-moving device 200 is not more than 0.3 degree. Therefore, the self-moving device 200 processes according to the differential correction data e sent by the base station 110, and the error is small within an acceptable range. Further, a distance between the base station and the GPS satellite is equal to a distance between the self-moving device and the GPS satellite, and the corrected positioning data of the self-moving device is most accurate at this time.

[0056] Further, the base station 110 can be in communication with a plurality of self-moving devices 200 at the same time, so that when the plurality of self-moving devices 200 work at the same time, the accurate positioning of the intelligent devices can be implemented, thereby greatly reducing the cost of the accurate positioning.

[0057] Further, a positioning method of a differential global positioning system of an embodiment of the present invention is described below. The differential global positioning system including a base station 110, where the base station 110 is configured to set first positioning data thereof when the base station is located at a fixed location, and includes an analysis module. The base station 110 is in communication connection with at least one intelligent device, and each self-moving device includes a processing module. The positioning method of a differential global positioning system includes at least the following steps:

[0058] Step 1: data acquisition: obtaining second positioning data of the base station according to a GPS positioning signals sent by a satellite-based positioning system, and transmitting the first positioning data and the second positioning data to the analysis module of the base station; and

[0059] Step 2: data analysis: receiving and analyzing, by the analysis module of the base station, the first positioning data and the second positioning data in the step 1 to obtain differential correction data of the base station, and transmitting the obtained differential correction data to the processing module of the intelligent device.

[0060] Further, the positioning method includes step 3: data processing: receiving, by the processing module of the intelligent device, the differential correction data, and correcting, according to the differential correction data, positioning data of the corresponding intelligent device at a current location obtained by the corresponding intelligent device by receiving the satellite-based positioning signals.

[0061] Further, at least one intelligent device includes an encoding module, and the encoding module is configured to encode the corresponding intelligent device to obtain a code; and the step 2 further includes: when the analysis module of the base station obtains the differential correction data of the base station through analysis, determining, by the base station, whether to transmit the differential correction data to the corresponding intelligent device according to whether the code matches preset data information of the base station.

[0062] Further, the base station includes a sending module for sending the differential correction data to the intelligent device, and a control module for storing the code of the intelligent device, and controlling whether the sending module sends the differential correction data to the intelligent device according to the code provided by the intelligent device.

[0063] Further, the intelligent device includes a control module, and the positioning method further includes step 4: instruction issuing: feeding back the positioning data corrected by the intelligent device to the instruction module, and controlling, by the instruction module, a moving path of the intelligent device, and sending out an execution instruction.

[0064] Further, the intelligent device includes an execution module, and the positioning method further includes step 5: instruction execution: receiving, by the execution module, the instruction issued by the instruction module, and triggering the intelligent device to travel according to the obtained moving path.

[0065] Further, the differential global positioning system includes at least two transmission paths for transmitting the differential correction data to the corresponding intelligent devices, and between the step 2 and the step 3, the method further includes: sending, by the corresponding intelligent device, an instruction to the base station to request for the differential correction data, and receiving, by the base station, the instruction, and instructing the corresponding intelligent device according to the different self-moving device to obtain the correct differential correction data through a corresponding transmission path.

[0066] The technical features of the embodiments may be in any combination. All possible combinations of the technical features in the embodiments are not described for brevity of description. However, as long as there is no contradiction between the combinations of these technical features, it should fall within the scope of the specification.

[0067] The embodiments above merely represent several embodiments of the present invention, and the description thereof is specific and detailed, but is not to be construed as a limitation on the protection scope of the present invention. It should be noted that any person skilled in the art may make some variations and modifications without departing from the concept of the present invention. Therefore, the protection scope of the present invention is subject to the attached claims.