JP6983125B2 - Wireless terminal, sensor data collection system and sensor data collection method - Google Patents

Description

The present invention relates to a wireless terminal, a sensor data collection system, and a sensor data collection method.

The IoT (Internet of Things), an M2M (Machine-to-Machine) system that connects wireless sensor terminals equipped with various sensors or connects wireless sensor terminals and servers on the cloud via a network and applies services, is currently being used. It is expected to be developed in various fields of use.

In Patent Document 1, in the sensor network system, a low power start-up sensor for detecting a change in the surrounding state is provided in addition to the measurement sensor with a large power consumption, and the measurement with a large power consumption is performed only when the surrounding state changes. It is disclosed that the power consumption of the sensor terminal is reduced by activating the sensor.

On the other hand, a battery can be represented by an equivalent circuit in which an electromotive force and an internal resistance are connected in series, and deterioration of the battery can be grasped as a phenomenon in which the internal resistance increases. For this reason, in the field of secondary batteries (storage batteries), although secondary batteries can be repeatedly charged and used, they gradually deteriorate and eventually become unable to charge / discharge operations. Technology for determining deterioration from the internal resistance of the next battery has been developed. Patent Document 2 describes that the remaining life of a lead storage battery is predicted from the internal resistance value of the storage battery at a predetermined temperature. Further, Patent Document 3 and Patent Document 4 describe that the internal resistance of a lithium ion battery is measured to detect the deterioration state and the replacement time of the battery.

Japanese Unexamined Patent Publication No. 2013-11963 Japanese Unexamined Patent Publication No. 2016-167336 Japanese Unexamined Patent Publication No. 2014-149280 Japanese Unexamined Patent Publication No. 2013-132147

It can be said that Patent Document 1 is effective in reducing power consumption as a whole in an event-driven sensor network system. However, in the terminal of the sensor network system where low power consumption is important, as a result of the progress of low power consumption of the processor and the wireless module, the sensor module may be the module having the highest power consumption during operation. .. In this case, if the battery that supplies power to the terminal is deteriorated, it may happen that the sensor module cannot be started. The same applies to Patent Document 1, and a situation may occur in which the measurement sensor cannot be activated even if the low power consumption activation sensor can be operated.

If a large current is supplied to the sensor module that consumes a large amount of power and the battery voltage generated by the battery drops significantly as a result, the power supply to the terminal's processor and high-frequency module will also be interrupted, so the terminal will be restarted. An operation to (reset) is required. When the wireless network adopts a low power consumption oriented mesh type (multi-hop type) network, it is necessary to reconstruct the network by resetting the terminals constituting the routing. In order to rebuild the network, it is necessary for each terminal to reconfirm the connection environment between terminals and search for appropriate routing, which leads to an increase in the power consumption of the entire system. .. Therefore, it is desirable to determine the deterioration of the battery, and if the sensor module with high power consumption is deteriorated to the extent that it cannot be started, it is desirable to prompt the battery replacement without starting the sensor module.

Conventionally, it has been widely practiced to monitor the battery voltage output by a battery to detect the remaining battery level. As described above, the battery can be expressed as an equivalent circuit in which the electromotive force and the internal resistance are connected in series. However, in a wireless sensor terminal whose current consumption is extremely reduced, the battery voltage is measured in a state where almost no current from the battery flows, so this measurement almost measures the electromotive force of the battery. , Does not reflect the magnitude of the internal resistance of the battery. For this reason, when a device that consumes a large current, such as a sensor module, is started with the internal resistance increasing due to deterioration of the battery, a large voltage drop due to the internal resistance of the battery appears and the battery voltage drops. , Power cannot be supplied to the terminal.

Patent Documents 2 to 4 determine the deterioration of the battery based on the internal resistance of the battery. Regarding the secondary battery, it is the same even in the primary battery that the internal resistance increases due to the deterioration of the battery. However, the usage scene is different from that of the present invention in which the power consumption is severely limited, and in the present invention, it is required to determine the deterioration of the battery in a state where the power consumption is as low as possible.

In the wireless terminal supplied with power from a battery, which is an embodiment of the present invention, a processor, a sensor module to which power is supplied from the battery by the processor during operation, and a plurality of constant current sources are connected in parallel. It has a battery voltage measuring circuit, and the processor receives a measurement request from the master unit and switches the conduction state of multiple constant current sources of the battery voltage measuring circuit multiple times while changing the load current of the battery. It measures the battery voltage output by the battery, receives a measurement execution request from the master unit, supplies power to the sensor module, and starts up. The measurement execution request is issued by the master unit when the sensor module determines that the sensor module can be started based on the internal resistance of the battery calculated from the battery voltage measured multiple times by changing the load current of the battery.

It is possible to monitor the remaining battery level of the wireless terminal with high accuracy, manage the life and death of the wireless terminal based on it, and collect highly reliable sensor data.

Other issues and novel features will become apparent from the description and accompanying drawings herein.

It is a block diagram of a terminal (slave unit). It is a block diagram of the M2M system to which the sensor data collection system was applied. It is a sensor data collection flowchart in a sensor data collection system. It is a figure explaining the calculation method of the internal resistance of a battery. It is a figure which shows the temperature dependence of the internal resistance of the battery with different deterioration states. It is a figure which shows the influence which the length of a load time has on the value of the calculated internal resistance. It is a measurement timing chart of a battery resistance.

FIG. 2 is a configuration diagram of an M2M system to which the sensor data collection system 203 of this embodiment is applied. The sensor data collection system 203 has a terminal (master unit) 204 and a plurality of terminals (slave units) 205, and forms a wireless area network. The terminal (master unit) 204 operates on a commercial power source, constructs a wireless area network by a plurality of terminals (slave units) 205, and executes control for collecting sensor data. An example of an application of an M2M system is to distribute terminals (slave units) having sensors mounted in predetermined fields and to realize a monitoring function by collecting sensor data from these terminals (slave units). .. In such an application, it is necessary for the distributed terminals (slave units) to operate stably for a long period of time and to maintain the network robustly even if some terminals (slave units) have problems in transmission / reception. Therefore, the sensor data collection system 203 adopts a low power consumption oriented mesh type (multi-hop type) network. In the mesh type network, for example, the sensor 206e measures the measurement request from the terminal (master unit) 204 to the terminal (slave unit) 205e, and the acquired sensor data is obtained from the terminal (slave unit) 205e and others. It is finally transmitted to the terminal (master unit) 204 via the terminal (slave unit) of.

The routing of the mesh network of the sensor data collection system 203 is managed by the terminal (master unit) 204. The terminal (master unit) 204 defines an optimum transmission route from the terminal terminal (slave unit) 205e to g to the terminal (master unit) 204, and the terminal (master unit) is used according to the defined transmission route. Commands and sensor data from the terminal (slave unit) are transmitted. The terminal (slave unit) 205 can be the same as the hardware regardless of whether or not the sensor is mounted. In this case, the number of sensors can be easily added in the field where the sensor data collection system 203 is formed. It is also possible that the terminals (slave units) 205e to g on which the sensor 206 is mounted execute the routing for transferring the sensor data.

Further, the sensor data collected by the sensor data collection system 203 and the type of the sensor also depend on the application of the M2M system and are not particularly limited. For example, it may be something like a temperature sensor, an optical sensor, a vibration sensor, a microphone module for acquiring voice data, or a camera module for acquiring still images or moving images. Further, the sensor data collected by the sensor data collection system 203 may be of a plurality of types. The sensor data may be the data itself acquired from the sensor, or may be processed data of the data acquired from the sensor. However, as the amount of sensor data to be transmitted increases, the power consumption required for the transmission increases. Therefore, it is desirable to transmit the data processed so that the amount of the sensor data to be transmitted becomes small as the sensor data. The frequency of collecting sensor data from the sensors 206e to g depends on the application, but in the case of applications for long-term monitoring of the presence or absence of abnormalities, it may be set to, for example, once an hour or once a day. Conceivable.

The sensor data from the sensors 206 distributed in the field is collected by the sensor data collection system 203 and aggregated in the gateway 202. The gateway 202 is connected to the server 200 that provides the application via the IP network 201. The server 200 uses the sensor data aggregated in the gateway 202 to provide a service such as execution of monitoring.

FIG. 1 shows a block diagram of the terminal (slave unit) 205. In this example, an example in which a camera module is mounted as a sensor 206 is shown. The terminal (slave unit) 205 operates by receiving power supply from the battery 100. As the battery 100, a primary battery such as a lithium thionyl chloride battery is used. In the figure, the battery 100 is shown as an equivalent circuit in which the electromotive force E and the internal resistance r are connected in series.

The RF (Radio Frequency) module 101 is a block that executes network management and transmission / reception of sensor data in the sensor data collection system 203. The main MCU (Microcontroller Unit) 102 is a block that executes sleep control of the mounted sensor 206, initialization of a terminal (slave unit), management of sensor data to be transmitted / received, and the like. Both the RF module (high frequency module) 101 and the main MCU (processor) 102 are low voltage modules excellent in low power consumption, and the power supply voltage obtained by stepping down the battery voltage V output by the battery 100 by the regulator 103 is the RF module 101. It is supplied to the main MCU 102.

The camera module 206 is a block that generates sensor data by taking a picture of a monitored object and analyzing the taken image. The camera module 206 is also supplied with a power supply voltage obtained by stepping down the battery voltage V output by the battery 100 via the regulator 104. Since the operation of the camera module 206 as a sensor consumes a large amount of power and its activation frequency is low, the main MCU 102 controls to supply a power supply voltage from the regulator 104 to the camera module 206 only when the camera module 206 is operated. This is aimed at reducing the power consumption of the terminal.

The RF module 101 and the main MCU 102 have a normal operation mode and a standby mode, respectively, in order to reduce power consumption during non-operation. For example, the RF module 101 has a current consumption of about 10 mA in the normal operation mode and a current consumption of about 0.03 mA in the standby mode, and the main MCU 102 has a current consumption of <1 mA in the normal operation mode and a current consumption in the standby mode. <0.01 mA. On the other hand, the current consumption during operation of the camera module is about 100 mA, which is larger than that of the RF module 101 and the main MCU 102.

The terminal (slave unit) 205 of this embodiment includes a battery voltage measuring circuit 120. The battery 100 outputs the main MCU 102 by dividing the resistance between the potential point N0 and the reference potential point by the resistance 105 and the resistance 106 and measuring the voltage of the potential point N1 between the resistance 105 and the resistance 106. Measure the battery voltage V. The resistance 105 is 1 MΩ and the resistance 106 is 2 MΩ, which limits the current flowing to the potential point N1. The calculation of the internal resistance of the battery using the battery voltage measuring circuit 120 will be described later.

FIG. 3 shows a flowchart of sensor data collection in the sensor data collection system 203. First, the terminal (master unit) 204 issues a measurement request command to a specific terminal (slave unit) 205s (S301). The terminal (slave unit) 205s received the measurement request command and measured the battery voltage a plurality of times while changing the amount of current using the battery voltage measuring circuit 120 and the temperature sensor provided in the terminal (slave unit) 205s. The temperature is transmitted to the terminal (master unit) 204 (S311). The terminal (master unit) 204 records the received plurality of battery voltages and temperatures (S302).

The terminal (master unit) 204 estimates the internal resistance of the battery from a plurality of battery voltages, determines the degree of deterioration of the battery from the estimated internal resistance and temperature of the battery, and determines whether or not the sensor module can be started (S303). .. When it is determined that the sensor module cannot be started, for example, a warning screen is displayed on the display of the terminal (master unit) 204 to prompt the terminal (slave unit) 205s to replace the battery. When it is determined that the sensor module can be activated, a measurement execution request command is issued to the terminal (slave unit) 205s (S305). The terminal (slave unit) 205s receives the measurement execution request command, activates the sensor module (S312), performs measurement, and transmits sensor data (S313). The terminal (master unit) 204 records the received sensor data (S306).

The method of calculating the internal resistance of the battery 100 in this embodiment will be described. First, the battery voltage measuring circuit 120 of the terminal (slave unit) 205 shown in FIG. 1 will be described. In the battery voltage measuring circuit 120, a plurality of constant current circuits 107 are connected in parallel between the potential point N0 and the reference potential point. In this example, three constant current circuits 107a to 107c are connected in parallel, but the number is not limited to three. In the constant current circuit 107, a constant current source 108, a light emitting diode 109, and a selection switch 110 are connected in series, and the selection switch 110 is ON / OFF controlled by the main MCU 102. In this example, the currents flowing through the constant current sources 108a to c are the same current i, but different current amounts may be used. The light emitting diode 109 is provided to visually confirm on the spot whether or not the battery has been replaced correctly when the battery is replaced, and may be omitted from the viewpoint of measuring the battery voltage.

The main MCU 102 of the terminal (slave unit) 205 measures the battery voltage V at that time while changing the load current of the battery 100 by switching the selection switch 110 (step S311 in FIG. 3). Specifically, in the case of FIG. 1, by making all the selection switches 110a to non-conducting (load current I ₀ , battery voltage V ₀ ), any one of the selection switches 110a to c is made conductive. (Load current I ₀ + i, battery voltage V ₁ ), by conducting any two of the selection switches 110a to 110 (load current I ₀ + 2i, battery voltage V ₂ ), selection switches 110a to c By conducting all of them, (load current I ₀ + 3i, battery voltage V ₃ ) can be measured.

The terminal (master unit) 204 obtains the internal resistance r of the battery 100 from the set of (load current I, battery voltage V). A method of calculating the internal resistance will be described with reference to FIG. The load current I is plotted on the horizontal axis, and the battery voltage V is plotted on the vertical axis. i is a current amount set by a constant current source, and is set as, for example, 10 mA to several tens of mA. Assuming that the battery voltage is measured with only the main MCU in the operating mode, the load current I ₀ is <1 mA. Therefore, if the average operating current during operation of the main MCU is assumed as the load current I _{0, the error can be ignored without actual measurement.} A straight line 401 that approximates the set of (load current I, battery voltage V) is obtained by, for example, the least squares method. Since the relationship of V = E-rI (E: electromotive force, r: internal resistance) is established, the internal resistance r of the battery 100 can be obtained from the slope θ of the straight line 401.

The internal resistance of a battery depends on its temperature. FIG. 5 shows the temperature dependence of batteries having different deterioration states, in which the horizontal axis represents the temperature (° C.) and the vertical axis represents the internal resistance r (Ω). The circles indicate the new battery 501, the squares indicate the battery 502 used to some extent, and the triangles indicate the temperature dependence of the internal resistance of the battery 503 when the remaining amount is almost 0. From this, it can be seen that the temperature dependence of the internal resistance differs depending on the deterioration state of the battery. Therefore, a threshold value 504 for determining deterioration (or battery replacement) at each temperature is set in advance. The terminal (slave unit) 205 is equipped with a temperature sensor and measures the temperature when the battery voltage is measured, and the terminal (master unit) 204 is internally calculated as a threshold value 504 at the temperature when the battery voltage V is measured. By comparing with the resistance r, it is determined whether or not the sensor module can be activated (step S303 in FIG. 3).

A modified example of this embodiment will be described below.

In FIG. 6, the internal resistance r is calculated multiple times with different load current flow times (load time), and the horizontal axis plots the load time (ms) and the vertical axis plots the calculated internal resistance r (Ω). It was done. The load current is 60 ms, and the battery voltage is measured after the load current is applied for a predetermined load time to obtain the internal resistance r. It can be seen that the shorter the load time, the smaller the power consumption of the battery, but if the load time is too short, the variation in the calculated internal resistance becomes large. In this experiment, an AA lithium thionyl chloride battery was used as the battery. It is considered that the cause of this is that electric power is generated by a chemical reaction in the battery, so that this chemical reaction is not stable when the load current is small, and the internal resistance r calculated as a result varies. ..

Therefore, in order to more accurately measure the battery voltage for calculating the internal resistance, the terminal (slave unit) 205 measures the battery voltage when the battery generates a predetermined amount of power and the output becomes stable. Try to do it. FIG. 7 shows a battery resistance measurement timing chart. Points 701 to 704 indicate the measurement timings of _{the battery voltages V 3} , V ₂ , V ₁ , and V _{0, respectively.}

In this way, by first measuring the battery voltage in the state where the load current is the largest, the time required for the battery output to stabilize can be shortened, and the time until the _{battery voltage V 3 is measured t 3} By extension, the time t ₀ required for all measurements can be shortened. However, the time t ₃ is set to be equal to or longer than the predetermined time T. T can be defined as the time required for the output of the battery to stabilize. Assuming that the battery exhibits the characteristics of FIG. 6 and i = 20 mA, it can be determined, for example, T = 100 ms. If the output of the battery stabilizes at the stage of point 701, the subsequent measurements may be performed in the minimum necessary time.

Although the invention made by the present inventor has been specifically described above based on the embodiment, the present invention is not limited to the above embodiment and can be variously modified without departing from the gist thereof. be. For example, it has been described that the sensor module startability determination is performed by the threshold value 504 based on the temperature dependence of the internal resistance of the battery shown in FIG. 5, but a plurality of threshold values are set to extend the battery life from an earlier stage. You may predict and issue an alarm. Further, in step S303, the remaining battery level estimated based on the temperature dependence of the internal resistance of the battery may be recorded. This makes it possible to grasp whether or not there is any abnormality in the progress of deterioration of the battery, and it becomes possible to perform more appropriate maintenance of the sensor data collection system.

Further, although the terminal (slave unit) 205s shows an example of measuring only the battery voltage in FIG. 3, the internal resistance of the battery may be calculated and the result may be transmitted to the terminal (master unit) 204. .. The simpler the calculation performed by the terminal (slave unit) 205s, the more the advantage is that it can be processed by a low power consumption processor. Since it is a trade-off with power consumption, change the division of roles between the calculation performed by the terminal (master unit) and the calculation performed by the terminal (slave unit) within the range allowed by the specifications of the power consumption of the wireless terminal. That is acceptable.

100: Battery, 101: RF module, 102: Main MCU, 103, 104: Regulator, 105, 106: Resistance, 107: Constant current circuit, 108: Constant current source, 109: Light emitting diode, 110: Select switch, 120: Battery voltage measurement circuit, 200: server, 201: IP network, 202: gateway, 203: sensor data collection system, 204: terminal (master unit), 205: terminal (slave unit), 206: sensor.

Claims (15)

A wireless terminal that is powered by batteries
With the processor
A sensor module whose power is supplied from the battery by the processor during operation, and
It has a battery voltage measuring circuit in which multiple constant current sources are connected in parallel.
In response to a measurement request from the master unit, the processor switches the conduction state of a plurality of constant current sources of the battery voltage measuring circuit, thereby changing the load current of the battery and outputting the battery a plurality of times. Measure the voltage,
The processor receives a measurement execution request from the master unit, supplies power to the sensor module, and starts up.
The measurement execution request is made when the sensor module determines that the sensor module can be started based on the internal resistance of the battery calculated from the battery voltage measured a plurality of times by the master unit by changing the load current of the battery. A wireless terminal issued by the machine. In claim 1,
A wireless terminal capable of communicating with the master unit by forming a mesh network with the master unit and other wireless terminals. In claim 1,
Has a temperature sensor,
The processor measures the temperature when the battery voltage output by the battery is measured by the temperature sensor, and then measures the temperature.
In the measurement execution request, the master unit compares the calculated internal resistance of the battery with the threshold value for determining whether or not the sensor module can be started at the temperature measured by the temperature sensor. A wireless terminal issued by the master unit when it is determined that the sensor module can be activated. In claim 1,
When the processor measures the battery voltage output by the battery a plurality of times while changing the load current of the battery, the wireless terminal first measures the battery voltage output by the battery with the load current maximized. .. In claim 4,
The processor measures the battery voltage output by the battery after a lapse of a predetermined time in a state where the load current is maximized.
The predetermined time is a wireless terminal determined based on the time required for the power supply from the battery to stabilize. In claim 1,
In the battery voltage measurement circuit, a plurality of constant current circuits in which the constant current source and the selection switch are connected in series are connected in parallel.
The processor is a wireless terminal that changes the load current of the battery by switching the conduction state of the selection switch of the plurality of constant current circuits. In claim 6,
The constant current circuit is a wireless terminal having a light emitting diode connected in series with the constant current source and the selection switch. With the parent machine
Each has multiple wireless terminals, powered by batteries,
The plurality of wireless terminals include a first wireless terminal having a sensor module to which power is supplied from the battery during operation.
By configuring the mesh type network of the plurality of wireless terminals, the first wireless terminal can communicate with the master unit.
In response to the measurement request from the master unit, the first wireless terminal measures the battery voltage output by the battery a plurality of times while changing the load current of the battery.
The first wireless terminal receives a measurement execution request from the master unit, supplies power to the sensor module, and starts up.
The measurement execution request is made when the sensor module determines that the sensor module can be started based on the internal resistance of the battery calculated from the battery voltage measured a plurality of times by the master unit by changing the load current of the battery. Sensor data collection system issued by the machine. In claim 8,
The first wireless terminal has a temperature sensor and has a temperature sensor.
The first wireless terminal measures the temperature when the battery voltage output by the battery is measured by the temperature sensor.
In the measurement execution request, the master unit compares the calculated internal resistance of the battery with the threshold value for determining whether or not the sensor module can be started at the temperature measured by the temperature sensor. A sensor data collection system issued by the master unit when it is determined that the sensor module can be activated. In claim 8,
When the first wireless terminal measures the battery voltage output by the battery a plurality of times while changing the load current of the battery, the first wireless terminal first measures the battery voltage output by the battery with the load current maximized. Sensor data collection system to measure. In claim 10,
The first wireless terminal measures the battery voltage output by the battery after a lapse of a predetermined time in a state where the load current is maximized.
The predetermined time is a sensor data collection system determined based on the time required for the power supply from the battery to stabilize. It is a sensor data collection method in a sensor data collection system having a master unit and a plurality of wireless terminals, each of which is supplied with power from a battery.
The plurality of wireless terminals include a first wireless terminal having a sensor module to which power is supplied from the battery during operation.
By configuring the mesh type network of the plurality of wireless terminals, the first wireless terminal can communicate with the master unit.
In response to the measurement request from the master unit, the first wireless terminal measures the battery voltage output by the battery a plurality of times while changing the load current of the battery.
The first wireless terminal receives a measurement execution request from the master unit, supplies power to the sensor module, and starts up.
The measurement execution request is made when the sensor module determines that the sensor module can be started based on the internal resistance of the battery calculated from the battery voltage measured a plurality of times by the master unit by changing the load current of the battery. Sensor data collection method issued by the machine. In claim 12,
The first wireless terminal has a temperature sensor and has a temperature sensor.
The first wireless terminal measures the temperature when the battery voltage output by the battery is measured by the temperature sensor.
In the measurement execution request, the master unit compares the calculated internal resistance of the battery with the threshold value for determining whether or not the sensor module can be started at the temperature measured by the temperature sensor. A sensor data collection method issued from the master unit when it is determined that the sensor module can be activated. In claim 12,
When the first wireless terminal measures the battery voltage output by the battery a plurality of times while changing the load current of the battery, the first wireless terminal first measures the battery voltage output by the battery with the load current maximized. Sensor data collection method to measure. In claim 14,
The first wireless terminal measures the battery voltage output by the battery after a lapse of a predetermined time in a state where the load current is maximized.
The predetermined time is a sensor data collection method determined based on the time required for the power supply from the battery to stabilize.

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