阅读说明：本技术 一种智能电能表的检定方法及装置 (Method and device for calibrating intelligent electric energy meter ) 是由 冯泽平 赵乾坤 曾驱虎 周帆 于 2020-12-30 设计创作，主要内容包括：本发明提供了一种智能电能表的检定方法,包括以下步骤：S10、主蓝牙模块和从蓝牙模块进行初始化对时。S20、检定开始后,主蓝牙模块和从蓝牙模块每间隔8-12ms进行一次时间同步,直至检定过程结束。S30、检定开始后,待检电能表向从蓝牙模块发送脉冲信号,从蓝牙模块将接收到的脉冲信号的序号、以及接收到脉冲信号的时间信息发送给主蓝牙模块。S40、主蓝牙模块接收从蓝牙模块传送的信息,并对所述信息进行电能误差计算,再将计算结果发送给显示单元。S50、显示单元显示电能误差结果。还提供了一种使用上述检定方法的检定装置。本发明提供的智能电能表的检定方法及装置,解决了无线检定方法抗干扰能力差的弱点,减小了检定误差,提高了检定结果的准确性。(The invention provides a method for calibrating an intelligent electric energy meter, which comprises the following steps: and S10, performing initialization time synchronization on the master Bluetooth module and the slave Bluetooth module. And S20, after the verification is started, the master Bluetooth module and the slave Bluetooth module perform time synchronization once at an interval of 8-12ms until the verification process is finished. S30, after the verification starts, the electric energy meter to be detected sends pulse signals to the slave Bluetooth module, and the slave Bluetooth module sends the sequence number of the received pulse signals and the time information of the received pulse signals to the master Bluetooth module. And S40, the master Bluetooth module receives the information transmitted by the slave Bluetooth module, performs electric energy error calculation on the information, and sends the calculation result to the display unit. And S50, displaying the power error result by the display unit. An assay device using the above assay method is also provided. The method and the device for calibrating the intelligent electric energy meter solve the defect of poor anti-jamming capability of a wireless calibration method, reduce calibration errors and improve the accuracy of calibration results.)

1. A verification method of an intelligent electric energy meter is characterized by comprising the following steps:

s10, performing initialization time synchronization on the master Bluetooth module and the slave Bluetooth module;

s20, after the verification is started, the master Bluetooth module and the slave Bluetooth module perform time synchronization once every 10-100ms until the verification process is finished;

s30, after the verification is started, the electric energy meter to be detected sends a pulse signal to the slave Bluetooth module, and the slave Bluetooth module sends the serial number of the received pulse signal and the time information of the received pulse signal to the master Bluetooth module;

s40, the master Bluetooth module receives the information transmitted by the slave Bluetooth module, performs electric energy error calculation on the information, and then sends the calculation result to the display unit;

and S50, displaying the power error result by the display unit.

2. The verification method of the intelligent electric energy meter according to claim 1, characterized in that: the master Bluetooth module and the slave Bluetooth module are both low-power Bluetooth modules based on BLE protocol.

3. The verification method of the intelligent electric energy meter according to claim 1, characterized in that: the initialization time setting in step S10 and the time synchronization in step S20 are both performed based on the physical layers of the master bluetooth module and the slave bluetooth module.

4. The verification method of the intelligent electric energy meter according to claim 1, characterized in that: the specific method for calculating the power error in step S40 is as follows:

the main Bluetooth module delays the received information for 30-100ms and then sends the information to an error calculation unit, and the error calculation unit receives the information and then carries out electric energy error calculation on the information.

5. The verification method of the intelligent electric energy meter according to claim 4, characterized in that: after receiving the information, the main Bluetooth module starts a first timer, and the first timer generates an interrupt and sends the information to an error calculation module; the first timer is set as follows:

time scale of slave bluetooth module pulse signal: tplosein;

current time scale: tpresent;

setting value of the first timer: tset;

fixing time delay: 30-100 msms;

Tset＝TpluseIn+(30-100ms)-Tpresent。

6. the verification method of the intelligent electric energy meter according to claim 1, characterized in that: the specific method for calculating the power error in step S40 is as follows:

the standard electric energy meter sends pulse data to the main Bluetooth module, the main Bluetooth module receives the pulse data, and the main Bluetooth module calculates electric energy errors of the received information and the pulse data in the main Bluetooth module.

7. The verification method of the intelligent electric energy meter according to claim 6, characterized in that: the slave Bluetooth module sends the information to the master Bluetooth module after digital processing, the master Bluetooth module receives pulse data of the standard meter and digitalizes the pulse data, when the number of pulses of the electric energy meter to be detected reaches a verification standard, calculation is carried out inside the master Bluetooth module, and an electric energy error calculation result is sent to the display unit in a wired or wireless mode.

8. The verification method of the intelligent electric energy meter according to claim 1, characterized in that: the specific content of step S10 is as follows: the second timer of the master Bluetooth module is interrupted once every 8-12ms, and after the first interruption, the master Bluetooth module initiates an initialization time setting request to the slave Bluetooth module;

and the third timer of the slave Bluetooth module is interrupted once every 8-12ms, and the slave Bluetooth module returns the time mark to 0 after receiving the initial time mark setting request of the master Bluetooth module.

9. The verification method of the intelligent electric energy meter according to claim 1, characterized in that: the specific content of step S20 is as follows: the master Bluetooth module initiates a time synchronization request to the slave Bluetooth module every 10-100ms, and the slave Bluetooth module corrects the time synchronization deviation by modifying the set interrupt value of the third timer after receiving the time synchronization request.

10. The utility model provides an intelligence electric energy meter calibrating installation which characterized in that: the intelligent electric energy meter calibrating device is calibrated by using the calibrating method of any one of claims 1 to 9 and comprises a master Bluetooth module, a slave Bluetooth module and a display unit;

the main Bluetooth module comprises a first chip based on a BLE protocol, a first timer and a second timer;

the slave Bluetooth module comprises a second chip based on BLE protocol and a third timer.

Technical Field

The invention relates to the technical field of electric energy meter verification, in particular to a verification method and device of an intelligent electric energy meter.

Background

The intelligent electric energy meter is an advanced metering device for collecting, analyzing and managing electric energy information data based on modern communication technology, computer technology and measurement technology. The basic principle of the intelligent electric energy meter is as follows: the current and the voltage of a user are collected in real time by depending on an A/D converter or a metering chip, analysis and processing are carried out by a CPU (Central processing Unit), calculation of forward and reverse, peak valley or four-quadrant electric energy is realized, and the contents such as electric quantity and the like are further output in the modes of communication, display and the like.

Generally, the number of pulses sent by the a/D converter when the intelligent electric energy meter measures one-hour is called pulse constant, which is an important constant for the intelligent electric energy meter, because how many pulses the a/D converter sends per unit time directly determines the accuracy of the measurement of the meter.

At present, the intelligent electric energy meter is usually calibrated in a wired connection mode, and the intelligent electric energy meter calibration has the advantages of small error and strong anti-interference capability. However, with the continuous progress of science and technology, the new generation of intelligent electric energy meter is a multi-core modularized intelligent electric energy meter, and the contact auxiliary terminal is cancelled at the end of the intelligent electric energy meter, so that the electric energy meter cannot be continuously calibrated by using a wired connection mode, and although the wireless connection mode is convenient to calibrate, the anti-interference capability of the wireless connection mode is weaker than that of the wired connection mode, so that the calibration error is larger.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provides a method and a device for calibrating an intelligent electric energy meter, so as to solve the defect of poor anti-jamming capability of a wireless calibration method, reduce calibration errors and improve the accuracy of a calibration result.

In order to achieve the purpose, the invention adopts the technical scheme that:

a verification method of an intelligent electric energy meter comprises the following steps:

s10, performing initialization time synchronization on the master Bluetooth module and the slave Bluetooth module;

s20, after the verification is started, the master Bluetooth module and the slave Bluetooth module perform time synchronization once every 10-100ms until the verification process is finished;

s30, after the verification is started, the electric energy meter to be detected sends a pulse signal to the slave Bluetooth module, and the slave Bluetooth module sends the serial number of the received pulse signal and the time information of the received pulse signal to the master Bluetooth module;

s40, the master Bluetooth module receives the information transmitted by the slave Bluetooth module, performs electric energy error calculation on the information, and then sends the calculation result to the display unit;

and S50, displaying the power error result by the display unit.

The further improvement of the technical scheme is as follows:

the master Bluetooth module and the slave Bluetooth module are both low-power Bluetooth modules based on BLE protocol.

The initialization time setting in step S10 and the time synchronization in step S20 are both performed based on the physical layers of the master bluetooth module and the slave bluetooth module.

The specific method for calculating the power error in step S40 is as follows:

the main Bluetooth module delays the received information for 30-100ms and then sends the information to an error calculation unit, and the error calculation unit receives the information and then carries out electric energy error calculation on the information.

After receiving the information, the main Bluetooth module starts a first timer, and the first timer generates an interrupt and sends the information to an error calculation module; the first timer is set as follows:

time scale of slave bluetooth module pulse signal: tplosein;

current time scale: tpresent;

setting value of the first timer: tset;

fixing time delay: 30-100 ms;

Tset＝TpluseIn+(30-100ms)-Tpresent。

the specific method for calculating the power error in step S40 is as follows:

the standard electric energy meter sends pulse data to the main Bluetooth module, the main Bluetooth module receives the pulse data, and the main Bluetooth module calculates electric energy errors of the received information and the pulse data in the main Bluetooth module.

The slave Bluetooth module sends the information to the master Bluetooth module after digital processing, the master Bluetooth module receives pulse data of the standard meter and digitalizes the pulse data, when the number of pulses of the electric energy meter to be detected reaches a verification standard, calculation is carried out inside the master Bluetooth module, and an electric energy error calculation result is sent to the display unit in a wired or wireless mode.

The specific content of step S10 is as follows: the second timer of the master Bluetooth module is interrupted once every 8-12ms, and after the first interruption, the master Bluetooth module initiates an initialization time setting request to the slave Bluetooth module;

and the third timer of the slave Bluetooth module is interrupted once every 8-12ms, and the slave Bluetooth module returns the time mark to 0 after receiving the initial time mark setting request of the master Bluetooth module.

The specific content of step S20 is as follows: the master Bluetooth module initiates a time synchronization request to the slave Bluetooth module every 10-100ms, and the slave Bluetooth module corrects the time synchronization deviation by modifying the set interrupt value of the third timer after receiving the time synchronization request.

The invention also provides an intelligent electric energy meter calibrating device which is calibrated by using the calibrating method and comprises a master Bluetooth module, a slave Bluetooth module and a display unit;

the main Bluetooth module comprises a first chip based on a BLE protocol, a first timer and a second timer;

the slave Bluetooth module comprises a second chip based on BLE protocol and a third timer.

According to the technical scheme, the method and the device for calibrating the intelligent electric energy meter perform time synchronization at intervals through the master Bluetooth module and the slave Bluetooth module, the slave Bluetooth module receives the pulse signal of the electric energy meter to be tested, converts the pulse signal and sends the converted pulse signal to the master Bluetooth module, and the master Bluetooth module further processes the information sent by the slave Bluetooth module so as to calibrate the electric energy meter. In the mode, the error is small and can be almost ignored, even if packet loss occurs in the transmission process, the error calculation module can be informed through communication, and the master Bluetooth module and the slave Bluetooth module can carry out time synchronization for dozens of times within one second, wherein only one time synchronization is successful, the time scales of the two parties can be ensured to be consistent, and the electric energy error obtained by carrying out reverse-pushing and compensation calculation by taking the time scales as a starting point has small influence on the error calculation.

Drawings

Fig. 1 is a schematic flow chart of a verification method of an intelligent electric energy meter according to embodiment 1 of the present invention.

Fig. 2 is a schematic flow chart of a verification method of an intelligent electric energy meter according to embodiment 2 of the present invention.

Detailed Description

To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

Fig. 1 and fig. 2 are schematic diagrams illustrating a flow of a verification method of an intelligent electric energy meter according to the present invention.

Example 1: the verification method of the intelligent electric energy meter comprises the following steps:

s10, performing initialization time synchronization on the low-power-consumption master Bluetooth module and the slave Bluetooth module based on the BLE protocol based on a physical layer (PHY);

the second timer of the master Bluetooth module is interrupted once every 8-12ms, and after the first interruption, the master Bluetooth module initiates an initialization time setting request to the slave Bluetooth module; the interval time in the embodiment is 10 ms;

the third timer of the slave Bluetooth module is interrupted once every 8-12ms, and the slave Bluetooth module counts time to 0 after receiving the initial time synchronization request of the master Bluetooth module; the interval time in this embodiment is 10 ms.

S20, after the verification is started, the master Bluetooth module and the slave Bluetooth module perform time synchronization once based on a physical layer (PHY) at intervals of 8-12ms until the verification process is finished;

the master Bluetooth module initiates a time synchronization request to the slave Bluetooth module every 8-12ms, and the slave Bluetooth module corrects the time synchronization deviation by modifying the set interrupt value of the third timer after receiving the time synchronization request.

S30, after the verification is started, the electric energy meter to be detected sends a pulse signal to the slave Bluetooth module, and the slave Bluetooth module sends information such as the serial number of the received pulse signal and the time of receiving the pulse signal to the master Bluetooth module;

the slave Bluetooth module receives the pulse sent by the intelligent electric energy meter to be detected and generates an interrupt, records the current time scale in the interrupt processing function, and then sends the current time scale to the master Bluetooth module through Bluetooth communication.

Time scale 4BYTE time range 65535 x 10ms 655.35s, cycle count 2BYTE (range 65535 cycles). With the time mark and the pulse counting mark, even if communication loss occurs, the main Bluetooth module can also know the time at the first time, so that the error calculation unit is informed to process the communication loss.

S40, the master Bluetooth module receives the information transmitted by the slave Bluetooth module, delays the received information by 30-50ms and then transmits the delayed information to the error calculation unit, and the error calculation unit receives the information, then carries out electric energy error calculation on the information and then transmits the calculation result to the display unit. The error unit comprises an analog power supply, a standard meter and an error board, and can be compatible with the existing error board. And the error unit compares the pulse data of the to-be-detected meter with the pulse data of the standard meter so as to verify the to-be-detected meter.

The delay time in this embodiment is 40ms, and specifically, after receiving the information, the main bluetooth module starts a first timer, and after the first timer is interrupted, the information is sent to the error calculation module; the first timer is set as follows:

time scale of slave bluetooth module pulse signal: tplosein;

current time scale: tpresent;

setting value of the first timer: tset;

fixing time delay: 40 ms;

Tset＝Tpluseln+40ms-Tpresent。

the error caused by the delay of 40ms is calculated, and both tables 1 and 2 are from the verification regulation of the JJG 597-.

TABLE 1 stability of output Power of the device

Accuracy class of device	Grade 0.01	Grade 0.02	Grade 0.03	Grade 0.05	Level 0.1	Grade 0.2	Grade 0.3
								Standard table method (%)	0.015	0.025	0.03	0.05	0.1	0.2	0.5
Watt-second method (%)	-	-	-	0.01	0.02	0.05	0.05

TABLE 2 Power stability

All pulse detection methods belong to the standard table method, so the detection method discussed in the invention is the standard table method. The verification time requirement of the electric energy meter is not less than 5 s. The limit error (power supply fluctuation happens in the last 40ms of 5s verification, and unidirectional maximum fluctuation happens) caused by the delay verification of 40ms is 0.5-0.004% (40ms/5 s). This error value is small and negligible for a 0.5 class (0.5%) power meter. In addition, the stability requirement required in table 2 is the maximum variation of 120s, and the experimental stability calculation is calculated as the maximum variation of 5s, so the actual maximum error value is far below 0.004%, and the occurrence probability thereof is extremely low.

Due to the existence of mutual interference of a plurality of slave modules and the running time of a Bluetooth protocol stack, under the general setting, the slave Bluetooth module receives a pulse signal of the electric energy meter to be detected, the master Bluetooth module receives the pulse signal of the slave Bluetooth module, the time delay is between 3ms and 6ms, and the purpose that the master Bluetooth module delays for 40ms and sends the pulse signal is used for compensating the error caused by the time delay, so that the anti-interference capability of the calibrating device is enhanced, and the calibrating error of the device is reduced.

And S50, displaying the power error result by the display unit.

Wherein BLE refers to Bluetooth Low Energy, i.e. Bluetooth Low Energy.

The timer is a very stable counter provided by the MCU itself, and the stable counter is a crystal oscillator component connected to the MCU.

Bluetooth software is generally divided into an application layer, a main protocol layer, and a control layer. According to the normal bluetooth application, if the time set for bluetooth pairing is T0 at the application layer, the time for reaching the physical layer through the HCI layer and the LL layer of the main protocol layer and the control layer is T0+ T1, and the time for different bluetooth chips and different operation states T1 is different, but is at least 2 ms. The inventor considers that the interference between Bluetooth requires a frequency hopping technology, and the frequency hopping is generated by adopting the frequency hopping technology, so that the delay T2 is caused, and the delay of T1+ T2 is measured to be about 3-6 ms. Therefore, the time synchronization must be performed by directly operating the register to perform time-stamping so as to avoid the error caused by the time delay, that is, the direct operation of the physical layer (PHY) is required to transmit data.

After the operation of the bluetooth protocol stack is started, some peripheral resources on the MCU, such as wireless transceiving hardware, a timer, etc., need to be accessed. After the bluetooth protocol stack is started, the bluetooth protocol stack has exclusive access to the resources, that is, after the bluetooth protocol stack is started, the external resources such as wireless transceiver hardware, timers and the like are not allowed to be directly accessed by the application layer, otherwise, the running state of the bluetooth protocol stack is damaged.

But for the BLE protocol itself, the operation of BLE is based on time intervals, i.e. periodic operation for a while and sleep for a while, which is also the essential principle of low power consumption. Therefore, when the BLE is in sleep, although the bluetooth protocol stack still "occupies" the resources of the wireless transceiving hardware, the timer and the like of the MCU, the bluetooth protocol stack does not use them, but even if not used, the application program cannot directly access these peripheral resources.

Some 2.4G communication is sometimes required while BLE is running, which is normally not possible. The bluetooth protocol stack however provides a solution for these resource applications that require access and bluetooth protocol stack conflicts-the TimeSlot, i.e. the time gap. The method is mainly characterized in that when the exclusive resources are not used in the running process of the Bluetooth protocol stack, an access interface is provided, so that the application program can temporarily use the resources in the interval, and the resources are released in time before the Bluetooth protocol stack needs to be used, thereby avoiding influencing the running state of the Bluetooth protocol stack.

Most bluetooth BLE chips on the market support a time slot usage pattern, and the program requests access to the wireless transceiver hardware between BLE activities. In the present invention, the time gap using BLE allows normal BLE activity to run simultaneously with the time synchronization function.

The second timer of the master Bluetooth module and the third timer of the slave Bluetooth module generate a deviation when timing interruption of 10ms occurs respectively, the deviation is the difference of crystal oscillators, the lowest precision of the Bluetooth crystal oscillators is 20ppm, the maximum difference between the two is 40ppm, and the deviation generated by interruption of 10ms is 0.4 us. While the 0.4us deviation is negligible for a minimum of 5 seconds of power metering time: the error is 0.000008%. Meanwhile, due to the interference problem of wireless transmission, the error caused by successful time synchronization once per second is 0.0008%, and the error has no influence on the verification result, so that the time synchronization method of the embodiment has strong anti-interference capability: the time error caused by the time synchronization rate of 1% has only 0.0008% influence on the electric energy.

The main Bluetooth module reads the value of the first timer register before sending information, and no error is generated in the sending operation delay, because the error mainly comes from the difference of the operation delay. Receiving a read value after interruption from a Bluetooth module, setting the interruption priority to be highest, and under the condition of considering nesting, according to the maximum interruption delay of 2us above a 32MHZ of a general 32-bit Bluetooth chip crystal oscillator, namely, the stack entering and exiting time is 64 data, but the actual code cannot write so many temporary variables. The error calculated as a difference of 2us is 0.00002%, which is very small and negligible.

Example of time stamp:

struct

{

signed short timer_10msval；

signed short timer_100nSval；

}sync_pkt；

timer _10msval is used to record how many 10ms runs. the inventor considers that the frequency division of the clock of the timer is 100ns, and obtains a value for convenient calculation, so that 100ns is selected, and actually the value can be modified according to the crystal oscillator of the Bluetooth chip, namely, each register count value represents 100 ns.

The register interrupted from the 10ms timer may be set by the difference of the second timer and the third timer, timer _100nsval, to synchronize the time difference of the two.

Example 2: the verification method of the intelligent electric energy meter in the embodiment is basically consistent with the steps of the embodiment 1, and the difference is that:

s40, the standard electric energy meter sends pulse data to the master Bluetooth module, the master Bluetooth module receives the pulse data, the master Bluetooth module carries out electric energy error calculation on the received information of the electric energy meter to be detected sent by the slave Bluetooth module and the pulse data sent by the standard electric energy meter, and then sends the calculation result to the display unit. The main Bluetooth module in the embodiment is internally integrated with the error board, so that the electric energy error can be calculated in the main Bluetooth module, and the integration level is higher.

The slave Bluetooth module digitalizes the information and sends the information to the master Bluetooth module, the master Bluetooth module simultaneously receives pulse data of the standard meter and digitalizes the pulse data, when the number of pulses of the electric energy meter to be detected reaches a verification standard, the master Bluetooth module performs calculation inside, and the electric energy error calculation result is communicated through a wire, such as a serial port; or wirelessly, such as bluetooth, WIFI, etc., to the display unit.

The digitization method has extremely strong anti-jamming capability, when 99 time pairs are carried out in 1 second, the consistency of the time scales of the two parties can be ensured as long as one time is successful, and the influence of the electric energy error obtained by reverse-deducing and adding compensation calculation by taking the time scales as a starting point on error calculation is small. The information sent from the Bluetooth communication module to the main Bluetooth module is digital and comprises the serial number of the pulse sent from the Bluetooth module and the arrival time of the pulse, so that even if the pulse of the electric energy meter at a certain time is lost due to interference, the error value can still be correctly calculated when the next pulse is accurately received. This is clearly seen from the following equation:

pulse constant of intelligent electric meter: k1;

standard table pulse constant: k2;

number of pulses of intelligent electric meter: nchk;

number of pulses of the standard meter: nstd;

error value E ═ (Nstd/K2-Nchk/K1)/Nstd/K2.

The minimum value of the number of pulses of the intelligent electric energy meter is set to be Nmin, the minimum value of the number of pulses of the intelligent electric energy meter to be detected is Nmin +1 due to Nmin data loss caused by interference, the error result is calculated by the minimum number of pulses of the corresponding standard meter through Nstdmin + n, and the calculation result is theoretically more accurate. According to the method, a main Bluetooth module receives pulse data sent by a slave Bluetooth module of the intelligent electric meter to be detected, and simultaneously receives pulse data sent by a standard electric energy meter, the received pulse data of the standard electric energy meter is earlier than the pulse data of the intelligent electric energy meter to be detected, theoretically, the error is 1/Nstd, when the pulse data of the standard electric energy meter to be detected is received successfully and is delayed, the number of the pulses of the standard electric energy meter which is received successfully in a delayed mode is more, the number of the pulses sent by the standard electric energy meter corresponding to the minimum value of the pulses of the electric energy meter to be detected twice is Nstdmin and Nstdmin + n, the corresponding error is E1-1/Nstdmin, E2-1/Nstdmin + n, and n >1, so E1 is less than E2.

Compared with other Bluetooth verification methods, the verification technical method is far better than other Bluetooth verification methods in terms of anti-interference, and an error calculation module can be omitted for the second embodiment.

Example 3: the embodiment provides an intelligent electric energy meter verification device, which is verified by using the verification method of embodiment 1 or embodiment 2 and comprises a master bluetooth module, a slave bluetooth module and a display unit;

the main Bluetooth module comprises a first chip based on a BLE protocol, a first timer and a second timer;

the slave Bluetooth module comprises a second chip based on BLE protocol and a third timer.

The method and the device for calibrating the intelligent electric energy meter realize wireless pulse calibration, make up for the defect of poor anti-interference capability of other Bluetooth pulse calibration methods, provide two different solutions aiming at different application scenes, and have good application prospects.

The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above examples only express preferred embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.