Data acquisition system, data acquisition method and program

Abstract

To make the numbers of data acquired from respective sensors within the same period correspond with each other.SOLUTION: A data acquisition system comprises: a plurality of sensor devices that have an oscillator for outputting a clock signal at a predetermined cycle, a sensor for detecting data at timing based on the clock signal, and a control unit; and an acquisition device that acquires the detected data from the plurality of sensor devices, wherein the acquisition device transmits a synchronization command to the plurality of sensor devices for each predetermined period, and the control unit includes: a number-of-times data acquisition unit that acquires number-of-times data corresponding to the number of times of detection of the data within a period from timing when the synchronization command has been acquired in the past to timing when the synchronization command is acquired this time; and a frequency adjustment unit that changes a frequency of the clock signal output by the oscillator when a divergence degree between reference number-of-times data and the number-of-times data is less than or equal to a predetermined value.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a data acquisition system, a data acquisition method, and a program.

Background Art

[0002] A method for acquiring data detected by a plurality of sensors at predetermined time intervals is known. For example, Patent Document 1 describes a vehicle control system having a plurality of sensor devices mounted on a vehicle and a control device, wherein the control device periodically transmits a measurement trigger signal to each sensor device, and each sensor device measures measurement data using the measurement trigger signal as a magnetic reference.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, there may be a case where it is required to associate the number of data acquired from each sensor within the same period.

[0005] The present invention has been made in view of the above, and an object thereof is to provide a data acquisition system, a data acquisition method, and a program capable of associating the number of data acquired from each sensor within the same period.

Means for Solving the Problems

[0006] In order to solve the above-described problems and achieve the object, a data acquisition system according to the present disclosure includes a plurality of sensor devices each having an oscillator that outputs a clock signal at a predetermined period, a sensor that detects data at a timing based on the clock signal, and a control unit, and an acquisition device that acquires the detected data from the plurality of sensor devices. The acquisition device transmits a synchronization command to the plurality of sensor devices every predetermined period, and the control unit includes a count data acquisition unit that acquires count data corresponding to the number of times the data is detected, which is the number of times of the period from the timing when the synchronization command was acquired last time to the timing when the synchronization command was acquired this time, and reference count data corresponding to a reference number of times of detection of the data, which is the number of times of the period from the timing when the synchronization command was acquired last time to the timing when the synchronization command was acquired this time. When the degree of deviation between the reference count data and the count data is equal to or less than a predetermined value, the control unit includes a frequency adjustment unit that changes the frequency of the clock signal output by the oscillator.

[0007] In order to solve the above-described problems and achieve the object, a data acquisition method according to the present disclosure is a data acquisition method using a plurality of sensor devices each having an oscillator that outputs a clock signal at a predetermined period and a sensor that detects data at a timing based on the clock signal, and an acquisition device that acquires the detected data from the plurality of sensor devices. The data acquisition method includes transmitting a synchronization command from the acquisition device to the plurality of sensor devices every predetermined period, acquiring count data corresponding to the number of times the data is detected, which is the number of times of the period from the timing when the synchronization command was acquired last time to the timing when the synchronization command was acquired this time, and when the degree of deviation between reference count data corresponding to a reference number of times of detection of the data, which is the number of times of the period from the timing when the synchronization command was acquired last time to the timing when the synchronization command was acquired this time, and the count data is equal to or less than a predetermined value, changing the frequency of the clock signal output by the oscillator.

[0008] In order to solve the above-described problems and achieve the object, a program according to the present disclosure causes a control unit to execute a data acquisition method using: a plurality of sensor devices each having an oscillator that outputs a clock signal at a predetermined period and a sensor that detects data at a timing based on the clock signal; and an acquisition device that acquires the detected data from the plurality of sensor devices, the program including: causing the acquisition device to transmit a synchronization command to the plurality of sensor devices at each predetermined period; acquiring, from the sensor devices, count data of the number of periods from the timing when the synchronization command was previously acquired to the timing when the synchronization command was acquired this time, the count data corresponding to the number of times the data is detected; acquiring reference count data of the number of periods from the timing when the synchronization command was previously acquired to the timing when the synchronization command was acquired this time, the reference count data corresponding to a reference number of times the data is detected; and changing the frequency of the clock signal output by the oscillator when a degree of deviation between the reference count data and the count data is equal to or less than a predetermined value.

Effect of the Invention

[0009] According to the present invention, it is possible to associate the number of data acquired from each sensor within the same period.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0011] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited by the embodiments described below.

[0012] (Data Acquisition System) FIG. 1 is a schematic block diagram of the data acquisition system according to the present embodiment. As shown in FIG. 1, the data acquisition system 1 according to the present embodiment includes a plurality of sensor devices 10 and an acquisition device 12 (logger). The sensor device 10 is a device that detects data. The acquisition device 12 acquires the data detected by the sensor device 10 from the plurality of sensor devices 10. In the example of the present embodiment, the number of acquisition devices 12 is one, but the present invention is not limited thereto, and a plurality of acquisition devices 12 may be provided. Further, the data acquisition system 1 has an arithmetic device (computer) (not shown), and the arithmetic device may perform arithmetic operations based on the data acquired by the acquisition device 12 (the data detected by each sensor device 10).

[0013] The data detected by the sensor device 10 may be arbitrary. However, in the present embodiment, the sensor device 10 detects data indicating the behavior of the vehicle C. That is, in the present embodiment, the sensor device 10 is mounted on the vehicle C and detects data indicating the behavior of the vehicle C when the vehicle C is traveling on the road. Further, the acquisition device 12 is also mounted on the vehicle C and acquires the data detected by the sensor device 10 (in this example, the data indicating the behavior of the vehicle C). However, the acquisition device 12 is not limited to being mounted on the vehicle C and may be provided at an arbitrary position. In this case, the data acquisition system 1 preferably has an arithmetic device (computer) (not shown), and the arithmetic device calculates the road surface condition of the road on which the vehicle C has traveled based on the data acquired by the acquisition device 12 (the data detected by each sensor device 10). The road surface condition is an index indicating the degree of unevenness of the road surface in the present embodiment. More specifically, in the present embodiment, the road surface condition is the IRI (International Roughness Index). However, the road surface condition is not limited to the IRI and may be any index indicating the state of the road surface. For example, the road surface condition may be at least one of the IRI, the flatness of the road surface, cracks, potholes, and the MCI (Maintenance Control Index).

[0014] The sensor device 10 may detect any data indicating the behavior of the vehicle C. In the present embodiment, it is preferable that the sensor device 10 detects the acceleration of the vehicle C as data. In this case, the sensor device 10 is an acceleration sensor that detects acceleration, and more preferably an acceleration sensor that detects acceleration in three axes. Further, the data detected by the sensor device 10 is not limited to acceleration, and for example, it may be at least one of acceleration, image data obtained by imaging the surroundings of the vehicle C, the speed of the vehicle C, the angular velocity of the vehicle C, the steering angle of the vehicle C, the braking amount of the vehicle C, the operation of the wiper of the vehicle C, the amount of operation of the suspension of the vehicle C, and the pressure of the vehicle C (for example, the pressure of the wheels). Note that since the image data around the vehicle C changes depending on the movement of the vehicle C, it can be said that it is information indicating the behavior of the vehicle C. The sensor device 10 that detects the captured image around the vehicle C is, for example, a camera, the sensor device 10 that detects the speed of the vehicle C is, for example, a speed sensor, the sensor device 10 that detects the speed of the vehicle C is, for example, a three-axis gyro sensor, the sensor device 10 that detects the steering angle of the vehicle C is, for example, a steering sensor, the sensor device 10 that detects the braking amount of the vehicle C is, for example, a brake sensor, the sensor device 10 that detects the operation of the wiper of the vehicle C is, for example, a wiper sensor, the sensor device 10 that detects the amount of operation of the suspension of the vehicle C is, for example, a suspension sensor, and the sensor device 10 that detects the pressure of the vehicle C may be, for example, a pressure sensor. Further, at least a part of the sensor device 10 may be configured to detect the position information of the vehicle C. The sensor device 10 that detects the position information of the vehicle C is, for example, a module for an IGS (Inertial Guidance System).

[0015] In the example of FIG. 1, the sensor device 10 includes a sensor device 10A provided above the left front wheel TR1 in the vertical direction, a sensor device 10B provided above the right front wheel TR2 in the vertical direction, a sensor device 10C provided above the left rear wheel TR3 in the vertical direction, and a sensor device 10D provided above the right rear wheel TR4 in the vertical direction. However, the position where the sensor device 10 is provided is arbitrary. Also, the number of sensor devices 10 is not limited to four, and may be any plurality. In the example of FIG. 1, the number of wheels TR is four, but the number is arbitrary and may be, for example, any number of two or more. In the example of FIG. 1, the sensor devices 10A to 10D detect the same type of data (here, acceleration), but each sensor device 10 may detect different types of data. For example, a sensor device 10 (for example, an acceleration sensor) that detects the same type of data and a sensor device 10 (for example, a speed sensor) that detects different data may be provided.

[0016] Note that the sensor device 10 is not limited to detecting data indicating the behavior of the vehicle C. For example, the sensor device 10 may be provided at an arbitrary location and detect arbitrary data at predetermined time intervals. For example, the sensor device 10 may be provided in a plant device and detect data (for example, pressure, temperature, rotation speed, load torque, etc.) indicating the behavior of the plant device when it is operating. In this case, the acquisition device 12 acquires data indicating the behavior of the device from each sensor device 10.

[0017] (Configuration of the sensor device) Next, the configuration of the sensor device 10 will be described. Unless otherwise specified, the structure and processing content of the sensor device 10 described hereinafter are common to all sensor devices 10.

[0018] FIG. 2 is a schematic block diagram of the sensor device. As shown in FIG. 2, the sensor device 10 includes an oscillator 20, a counter 21, a sensor 22, a storage unit 24, a communication module 26, and a control unit 28.

[0019] (Oscillator) The oscillator 20 outputs a clock signal at a predetermined period. In this embodiment, the oscillator 20 includes an oscillation element 20A that outputs a clock signal at a constant period. For example, examples of the oscillation element 20A include a crystal oscillator, a SAW (Surface Acoustic Wave) oscillator, and a ceramic oscillator. Also, in this embodiment, the oscillator 20 can adjust the frequency (period) of the output clock signal. Note that the frequency of the clock signal refers to the number of clock signals output per unit time (for example, 1 second). The oscillator 20 may have any configuration capable of adjusting the frequency of the clock signal, but in this embodiment, as shown in FIG. 2, in addition to the oscillation element 20A, it has a frequency adjuster 20B, an analog signal generator 20C, frequency dividers 20D, and 20E.

[0020] The frequency adjuster 20B is a circuit that adjusts the frequency of the clock signal output from the oscillation element 20A. For example, the frequency adjuster 20B may control the frequency control voltage input and control the frequency of the clock signal from the oscillation element 20A by adjusting the reactance of the oscillation element 20A using a variable capacitance diode or the like.

[0021] The analog signal generator 20C is a circuit that converts a frequency adjustment command (a command to change the frequency), which is a digital signal from the control unit 28 (the frequency adjustment unit 36 described later), into an analog signal. The frequency adjustment command converted into an analog signal by the analog signal generator 20C is input to the frequency adjuster 20B. The frequency adjuster 20B adjusts the frequency of the clock signal from the oscillation element 20A to a frequency corresponding to the frequency adjustment command. Examples of the analog signal generator 20C include a PWM (Pulse Width Modulation) circuit and a DAC (Digital Analogue Converter) circuit.

[0022] The clock signal output by the oscillator 20 (oscillator element 20A) serves as a reference for the timing at which the sensor device 10 (sensor 22 described later) having the oscillator 20 detects data. The frequency of the clock signal output by the oscillator 20 may be arbitrary, but for example, it is preferably 1 MHz or more and 100 MHz or less. The sensor 22 performs detection at a sampling rate corresponding to the clock signal from the oscillator 20. In the present embodiment, a frequency divider 20E is connected to the oscillator element 20A, and in the frequency divider 20E, the clock signal from the oscillator 20 is divided to generate a detection clock signal. The sensor 22 acquires this detection clock signal and performs detection at a sampling rate corresponding to the detection clock signal. The frequency of the detection clock signal is lower than the frequency of the clock signal and may be, for example, 100 Hz or more and 1000 kHz or less. By outputting a high-frequency clock signal and dividing it for use in this way, the fineness of adjustment of the sampling rate of the sensor 22 described later can be realized, and furthermore, the sampling itself can be speeded up, and data can be detected in a short cycle. Also, the frequency of the clock signal and the frequency of the detection clock signal are preferably higher than the switching frequency of the time slot (the frequency at which the acquisition device 12 switches the communication target) described later.

[0023] The clock signal output by the oscillator 20 (oscillator element 20A) serves as a reference for the timing at which the sensor device 10 having the oscillator 20 (counter 21 described later) counts the number of times data described later. The counter 21 performs detection at a sampling rate corresponding to the clock signal from the oscillator 20. In the present embodiment, a frequency divider 20D is connected to the oscillator element 20A, and in the frequency divider 20D, the clock signal from the oscillator 20 is divided to generate a clock signal for counting. The counter 21 acquires this clock signal for counting and performs counting using the clock signal for counting. The frequency of the clock signal for counting is lower than the frequency of the clock signal. Also, it is preferable that the frequency of the clock signal for counting is different from the frequency of the clock signal for detection, and in the present embodiment, it is higher than the frequency of the clock signal for detection. Since the clock signal for counting and the clock signal for detection are obtained by dividing the clock signal from the oscillator 20, it can be said that they correspond to each other (here, they are proportional). The frequency of the clock signal for counting may be, for example, about 100 to 10,000 times that of the clock signal for detection, and may be 1 kHz or more and 1000 kHz or less. In this way, by counting the clock signal for counting having a frequency higher than the frequency of the clock signal for detection as the number of times data, fluctuations in the frequency of the clock signal can be appropriately detected and the frequency can be appropriately adjusted. Note that it is preferable that the frequency of the clock signal for counting is higher than the switching frequency of the time slot (the frequency at which the acquisition device 12 switches the communication target) described later.

[0024] In this embodiment, as described above, the detection clock signal is generated using the frequency divider 20D, and the counting clock signal is generated using the frequency divider 20E. However, the present invention is not limited thereto, and one frequency divider capable of dividing to different frequencies may be used to generate the detection clock signal and the counting clock signal. Further, it is not essential to generate the detection clock signal by dividing the clock signal. That is, the detection clock signal may be any signal whose frequency corresponds (is proportional) to the frequency of the clock signal. For example, the clock signal itself may be used as the detection clock signal for detection by the sensor 22. Similarly, it is not essential to generate the counting clock signal by dividing the clock signal. That is, the counting clock signal may be any signal whose frequency corresponds (is proportional) to the frequency of the clock signal. For example, the clock signal itself may be used as the counting clock signal for counting by the counter 21.

[0025] (Counter) The counter 21 is a circuit that counts the number of times a signal is received. The counter 21 receives the counting clock signal. Each time the counter 21 receives the counting clock signal, it accumulates the count number and stores the number of times the counting clock signal has been received as count data in the counter 21 itself or the storage unit 24.

[0026] (Sensor) The sensor 22 is a sensor that detects data. That is, for example, when detecting the acceleration of the vehicle C, the sensor 22 is an acceleration sensor. The sensor 22 performs detection each time it receives the detection clock signal. Details of the detection by the sensor 22 will be described later.

[0027] (Storage unit) The storage unit 24 is a memory that stores various information such as the calculation content and programs of the control unit 28, and data detected by the sensor 22. For example, it includes at least one of a main storage device such as a RAM (Random Access Memory) and a ROM (Read Only Memory), and a non-volatile storage device such as a flash memory or an SSD (Solid State Disk Drive). Note that the program for the control unit 28 stored by the storage unit 24 may be stored in a recording medium readable by the sensor device 10.

[0028] (Communication module) The communication module 26 is a module that communicates with an external device (here, the acquisition device 12). The communication module 26 may be any module capable of communicating with an external device, but in this embodiment, it wirelessly communicates with the acquisition device 12. Further, the communication module 26 of this embodiment is a Bluetooth (registered trademark) module. The communication module 26 of this embodiment internally allocates time slots (periods) to transmit and receive data with the acquisition device 12. In other words, before the start of communication, the communication module 26 negotiates a time slot during which it can communicate with the acquisition device 12, and during communication, it uses that time slot (period during which communication is possible) to perform communication. That is, the communication module 26 transmits and receives data with the acquisition device 12 at predetermined intervals, and it can be said that the interval is fixed. For example, the protocol stack of the communication module 26 is composed of multiple layers, and a time slot during which communication with the acquisition device 12 is possible is set inside the communication module by the lower layer. In this embodiment, since a general-purpose communication module 26 is used, without adjusting the lower layer that allocates time slots, it can be said that the time slots for transmitting and receiving data are fixed. That is, when using a general-purpose communication module 26, in the lower layer (protocol stack inside the communication module), a time slot during which communication is permitted is automatically allocated, and communication cannot be performed at a free timing. Note that the time slots being fixed means that the order in the time series of the periods (time slots) during which each sensor device 10 can communicate with the acquisition device 12 cannot be changed. That is, taking two sensor devices 10A and 10B as an example, the first time slot during which the sensor device 10A (the first sensor device) can communicate with the acquisition device 12 and the second time slot during which the sensor device 10B (the second sensor device) can communicate with the acquisition device 12 are set in this order in the time series, and this order is fixed and cannot be changed.

[0029] (Control unit) The control unit 28 is an arithmetic unit and includes an arithmetic circuit such as a CPU (Central Processing Unit). The control unit 28 includes a sensor control unit 30, a communication control unit 32, a count data acquisition unit 34, and a frequency adjustment unit 36. The control unit 28 reads a program (software) from the storage unit 24 and executes it to implement the sensor control unit 30, the communication control unit 32, the count data acquisition unit 34, and the frequency adjustment unit 36, and executes their processes. Note that the control unit 28 may execute these processes by one CPU, or may include a plurality of CPUs and execute the processes by these plurality of CPUs. Further, at least a part of the sensor control unit 30, the communication control unit 32, the count data acquisition unit 34, and the frequency adjustment unit 36 may be implemented by dedicated hardware.

[0030] The processing contents of each part of the control unit 28 will be described later.

[0031] (Configuration of the acquisition device) Next, the configuration of the acquisition device 12 will be described. FIG. 3 is a schematic block diagram of the acquisition device. As shown in FIG. 3, the acquisition device 12 includes an oscillator 40, a storage unit 42, a communication module 44, and a control unit 46.

[0032] (Oscillator) The oscillator 40 outputs a clock signal at a predetermined period. The oscillator 40 has an oscillation element that outputs a clock signal at a constant period. For example, examples of the oscillation element include a crystal oscillator and a ceramic oscillator. Similar to the oscillator 20 of the sensor device 10, the oscillator 40 may be able to adjust the frequency of the clock signal, or the frequency of the clock signal may be fixed. The clock signal output by the oscillator 40 serves as a reference for the timing of outputting a synchronization command described later. The frequency of the clock signal output by the oscillator 40 may be arbitrary, but is preferably, for example, 1 MHz or more and 100 MHz or less.

[0033] (Storage unit) The storage unit 42 is a memory that stores various types of information such as the calculation content, programs, and data transmitted from the sensor device 10 of the control unit 46. For example, it includes at least one or more of a main storage device such as a RAM and a ROM, and a non-volatile storage device such as a flash memory and an HDD. Note that the program for the control unit 46 stored by the storage unit 42 may be stored in a recording medium readable by the acquisition device 12.

[0034] (Communication module) The communication module 44 is a module that communicates with an external device (here, the sensor device 10). The communication module 44 may be any module capable of communicating with an external device, but in this embodiment, it communicates wirelessly with the sensor device 10. Furthermore, the communication module 44 of this embodiment is a Bluetooth module. Similar to the communication module 26 of the sensor device 10, the communication module 44 of this embodiment may have time slots for transmitting and receiving data with two or more counterpart devices (here, the sensor device 10) fixed for each sensor device 10. Note that, although details will be described later, the communication between the sensor device 10 and the acquisition device 12 via the communication modules 26 and 44 is performed using time-division time slots.

[0035] (Control unit) The control unit 46 is an arithmetic device and includes an arithmetic circuit such as a CPU. The control unit 46 includes a synchronization command generation unit 50 and a communication control unit 52. The control unit 46 reads and executes a program (software) from the storage unit 42 to realize the synchronization command generation unit 50 and the communication control unit 52 and execute their processes. Note that the control unit 46 may execute these processes with one CPU, or may be provided with a plurality of CPUs and execute the processes with those plurality of CPUs. Also, at least a part of the synchronization command generation unit 50 and the communication control unit 52 may be realized by dedicated hardware.

[0036] The processing content of each part of the control unit 46 will be described later.

[0037] (Processing of the data acquisition system) Next, the processing content of the data acquisition system 1 will be described.

[0038] (Detection of data) The sensor control unit 30 of the sensor device 10 controls the sensor 22 to detect data on the sensor 22. The sensor control unit 30 causes the sensor 22 to detect data at a timing based on the detection clock signal output from the oscillator 20. In the present embodiment, the sensor control unit 30 causes the sensor 22 to detect data every time a detection clock signal is output from the oscillator 20. Therefore, in the present embodiment, the frequency (period) of data detection by the sensor 22 coincides with the frequency (period) at which the detection clock signal is output. Note that the frequency of data detection by the sensor 22 refers to the number of times the sensor 22 performs detection per unit time (for example, 1 second).

[0039] The above data detection process is performed for each sensor device 10.

[0040] (Transmission of data) FIG. 4 is a time chart showing an example of data transmission. The data detection period in FIG. 4 refers to the period during which the sensor device 10 detects data, and the data transmission period refers to the period during which the sensor device 10 transmits data to the acquisition device 12. The communication control unit 32 of the sensor device 10 controls the communication module 26 to transmit the data detected by the sensor 22 from the communication module 26 to the acquisition device 12. The sensor device 10 and the acquisition device 12 perform data transmission and reception in a time-division manner. That is, in the present embodiment, a time slot for performing data transmission and reception with the acquisition device 12 is set for each sensor device 10, and different time slots in different time zones are set for each sensor device 10. That is, each time slot is assigned in a round-robin manner according to the number of communication partners.

[0041] For example, in FIG. 4, the time slots TAn assigned to the sensor device 10A, the time slots TBn assigned to the sensor device 10B, the time slots TCn assigned to the sensor device 10C, and the time slots TDn assigned to the sensor device 10D are set in a round-robin manner so as to be repeated in this order in time series. That is, in the time slots TAn, TBn, TCn, TDn, if a numerical value is described for n, it means that it is behind in time series in the order of increasing the numerical value. In FIG. 4, the time slots TA1 to TD2 are illustrated as the time slots TAn, TBn, TCn, TDn assigned in a round-robin manner. That is, in the example of FIG. 4, the time slot TA1 assigned to the sensor device 10A, the time slot TB1 assigned to the sensor device 10B, the time slot TC1 assigned to the sensor device 10C, the time slot TD1 assigned to the sensor device 10D, the time slot TA2 assigned to the sensor device 10A (the time slot assigned to the sensor device 10A immediately after the time slot TA1), the time slot TB2 assigned to the sensor device 10B, the time slot TC2 assigned to the sensor device 10C, and the time slot TD2 assigned to the sensor device 10D are set in this order along the time series.

[0042] The length of the time slot may be set as appropriate, but in the present embodiment, it is longer than the interval between the detection timings of the sensors 22 (the time from when one detection is performed until the next detection is performed). In other words, if the number of time slots in a unit time (for example, 1 second) (the number of times the time slot is switched in a unit time) is defined as the switching frequency of the time slot, the switching frequency of the time slot is lower than the frequency of data detection by the sensor 22 (the frequency of the detection clock signal). The switching frequency of the time slot is preferably, for example, 50 Hz or more and 500 Hz or less.

[0043] In the time slot assigned to its own sensor device 10, the communication control unit 32 transmits the data detected by the sensor 22 to the acquisition device 12. The communication control unit 32 transmits each piece of data detected during the period from the time slot in which data was last transmitted to the current time slot to the acquisition device 12 in the current time slot. For example, in FIG. 4, the sensor device 10A transmits each piece of data detected during the period from time slot TA1 to immediately before time slot TA2 to the acquisition device 12 within the period of time slot TA2. Similarly, the sensor device 10B transmits each piece of data detected during the period from time slot TB1 to immediately before time slot TB2 to the acquisition device 12 within the period of time slot TB2. Similarly, the sensor device 10C transmits each piece of data detected during the period from time slot TC1 to immediately before time slot TC2 to the acquisition device 12 within the period of time slot TC2. Similarly, the sensor device 10D transmits each piece of data detected during the period from time slot TD1 to immediately before time slot TD2 to the acquisition device 12 within the period of time slot TD2.

[0044] (Data acquisition) The communication control unit 52 of the acquisition device 12 controls the communication module 44 to acquire the data (the data detected by the sensor 22) transmitted from each sensor device 10 via the communication module 44. The acquisition device 12 switches the communication target among a plurality of sensor devices 10 every time slot (a predetermined period) to perform data transmission and reception. That is, in the example of FIG. 4, the data detected by the sensor device 10A during the period from the time slot TA1 to immediately before the time slot TA2 is transmitted from the sensor device 10A and received by the acquisition device 12 within the period of the time slot TA2. Similarly, the data detected by the sensor device 10B during the period from the time slot TB1 to immediately before the time slot TB2 is transmitted from the sensor device 10B and received by the acquisition device 12 within the period of the time slot TB2. Similarly, the data detected by the sensor device 10C during the period from the time slot TC1 to immediately before the time slot TC2 is transmitted from the sensor device 10C and received by the acquisition device 12 within the period of the time slot TC2. Similarly, the data detected by the sensor device 10D during the period from the time slot TD1 to immediately before the time slot TD2 is transmitted from the sensor device 10D and received by the acquisition device 12 within the period of the time slot TD2.

[0045] The acquisition device 12 stores the data (the data detected by the sensor 22) acquired from each sensor device 10 in the storage unit 42.

[0046] (The number of data to be acquired) Here, there may be a case where it is required that the number of data acquired from the sensor device 10 by the acquisition device 12 within the same period corresponds among the simultaneously connected sensor devices 10. Here, "the number of data corresponding to each sensor device 10" means that the number of data transmitted from the sensor device 10 to the acquisition device 12 is the same for any of the simultaneously connected sensor devices 10, but it is not limited to this. It may also mean that the number of data transmitted for each sensor device 10 approaches as close as possible to the same number within the same time, or that the ratio between the numbers of data approaches as close as possible to a predetermined ratio. By making the number of data correspond to each sensor device 10 in this way, it becomes possible to appropriately associate the data of each sensor device 10, and for example, the data of each sensor device 10 can be effectively used such as appropriately calculating road surface information.

[0047] As described above, each sensor device 10 detects data at a frequency corresponding to the frequency of the clock signal from the oscillator 20 built in the sensor device 10 (the frequency of the detection clock signal in this embodiment). Therefore, the number of data detected by the sensor 22 and transmitted to the acquisition device 12 within a certain period is determined according to the frequency of the clock signal from the oscillator 20. Therefore, in this embodiment, the frequencies of the clock signals of the respective sensor devices 10 are set to corresponding values (for example, the same value or a predetermined ratio) so that the number of data corresponds to each sensor device 10. However, the frequency of the clock signal may vary depending on the usage environment such as the temperature of the oscillator 20. In such a case, the frequency of the clock signal may shift for each sensor device 10, and the number of data for each sensor device 10 may fail to correspond. On the other hand, in this embodiment, as will be described later, each sensor device 10 finely adjusts the frequency of the clock signal of the oscillator 20 triggered by the transmission of the synchronization command from the acquisition device 12. Thereby, it becomes possible to appropriately associate the number of data for each sensor device 10. The following specifically describes this process.

[0048] (Generation of Synchronization Command) FIG. 5 is a time chart for explaining an example of generation and transmission of a synchronization command. A synchronization command generation unit 50 of the acquisition device 12 generates a synchronization command Cn. The synchronization command Cn is a signal that serves as a trigger for frequency adjustment of the clock signal of the oscillator 20 by the sensor device 10. The synchronization command generation unit 50 generates the synchronization command Cn at a timing based on the clock signal output from the oscillator 40. In the present embodiment, a frequency divider (not shown) is provided in the oscillator 40, and the clock signal generated by the oscillator 40 is divided by the frequency divider. The synchronization command generation unit 50 generates the synchronization command Cn every time the divided clock signal is output. The clock signal divided by the frequency divider may be output, for example, about once per second. Therefore, in the present embodiment, the frequency (period) at which the synchronization command Cn is generated coincides with the frequency (period) obtained by dividing the clock signal from the oscillator 40 at a certain ratio. However, the frequency at which the synchronization command Cn is generated is not necessarily the frequency obtained by dividing the frequency of the clock signal from the oscillator 40. For example, the frequency at which the synchronization command Cn is generated may be the same as the frequency of the clock signal from the oscillator 40. The frequency at which the synchronization command Cn is generated is preferably, for example, about 0.1 Hz to 10 Hz. Note that the frequency at which the synchronization command Cn is generated refers to the number of times the synchronization command Cn is generated per unit time (for example, one second).

[0049] The synchronization command generation unit 50 generates a synchronization command for each sensor device 10. Therefore, in the present embodiment, the synchronization command generation unit 50 generates a synchronization command Cn for each sensor device 10 every time a trigger pulse (divided clock signal) obtained by appropriately dividing the clock signal from the oscillator 40 is output. Here, the timing at which the clock signal is output from the oscillator 40 and the period of the clock signal are determined regardless of the time slot assigned to each sensor device 10. Therefore, the timing at which the clock signal is output from the oscillator 40 and the period of the clock signal may or may not be synchronized with the time slot assigned to each sensor device 10. In the present embodiment, they are not synchronized. In other words, the timing and period at which the synchronization command Cn is generated may or may not coincide with the start timing and period of the time slot of each sensor device 10. In the present embodiment, they do not coincide.

[0050] In the example of FIG. 5, since the clock signal (divided clock signal in this example) from the oscillator 40 is output at the timing during the time slot immediately before the time slot TA1, the synchronization command generation unit 50 generates the synchronization command C1 for each sensor device 10 using that clock signal as a trigger. Then, in the example of FIG. 5, since the next clock signal (divided clock signal in this example) from the oscillator 40 is output at the timing during the time slot TB2, the synchronization command generation unit 50 generates the synchronization command C2 (the synchronization command generated next to the synchronization command C1) for each sensor device 10 using that clock signal as a trigger. However, the timing and period (frequency) for generating the synchronization commands in FIG. 5 are just examples. Also, the synchronization command generation unit 50 may configure the synchronization command Cn so that one synchronization command Cn can be broadcast to each of the sensor devices 10A to 10D at the same time, or may be configured to sequentially send individual synchronization commands Cn to each of the sensor devices 10A to 10D. For example, in FIG. 5, the synchronization command generation unit 50 generates the synchronization commands Cn for the sensor devices 10A to 10D at the same timing, but it is not limited to this, and the synchronization commands Cn for the sensor devices 10A to 10D may be generated individually and sequentially.

[0051] Note that the synchronization command Cn may be any signal as long as the sensor device 10 can identify that the signal is the synchronization command Cn (identification information). However, in this embodiment, it is preferable that the synchronization command Cn includes transmission count information in addition to the identification information. The transmission count information is information indicating the number of times the synchronization command Cn is transmitted to the sensor device 10. In other words, it is information indicating which time the synchronization command Cn generated this time is being transmitted to the sensor device 10. That is, for example, if the synchronization command has been transmitted 4 times to the sensor device 10A so far, the transmission count information of the synchronization command Cn generated this time for the sensor device 10A is information indicating that it is the 5th time.

[0052] (Transmission of Synchronization Command) The communication control unit 52 of the acquisition device 12 controls the communication module 44 to transmit a synchronization command Cn from the communication module 44 to each sensor device 10. As described above, in the present embodiment, a time slot for transmitting and receiving data with the sensor device 10 is set for each sensor device 10. Therefore, the communication control unit 52 transmits the synchronization command Cn to the target sensor device 10 in the time slot assigned to the target sensor device 10. In this case, the communication control unit 52 transmits the synchronization command Cn to the sensor device 10 in the time slot assigned to the sensor device 10 immediately after generating the synchronization command Cn.

[0053] For example, in FIG. 5, the communication control unit 52 transmits the synchronization command C1 for the sensor device 10A generated immediately before the time slot TA1 to the sensor device 10A within the period of the time slot TA1. Similarly, the communication control unit 52 transmits the synchronization command C1 for the sensor device 10B generated immediately before the time slot TA1 to the sensor device 10B within the period of the time slot TB1. Similarly, the communication control unit 52 transmits the synchronization command C1 for the sensor device 10C generated immediately before the time slot TA1 to the sensor device 10C within the period of the time slot TC1. Similarly, the communication control unit 52 transmits the synchronization command for the sensor device 10D generated immediately before the time slot TA1 to the sensor device 10D within the period of the time slot TD1.

[0054] Also, in FIG. 5, the communication control unit 52 transmits the synchronization command C2 for the sensor device 10A generated during the time slot TB2 to the sensor device 10A within the period of the time slot TA3 (the time slot TAn immediately following the time slot TB2). The communication control unit 52 transmits the synchronization command C2 for the sensor device 10B generated during the time slot TB2 to the sensor device 10B within the period of the time slot TB3 (the time slot TBn immediately following the time slot TB2). The communication control unit 52 transmits the synchronization command C2 for the sensor device 10C generated during the time slot TB2 to the sensor device 10C within the period of the time slot TC2. The communication control unit 52 transmits the synchronization command C2 for the sensor device 10D generated during the time slot TB2 to the sensor device 10D within the period of the time slot TD2.

[0055] Thus, when a plurality of sensor devices 10 are connected to the acquisition device 12, the synchronization command Cn is independently generated and transmitted to each sensor device 10 by the same trigger (the same clock signal). As shown in FIG. 5, actual communication will be sent if there is a time slot in which the synchronization command Cn can be sent (i.e., the time slot assigned immediately after the creation of the synchronization command Cn), and the simultaneity of transmission for each sensor device 10 is not guaranteed. Also, since it is not known from which time slot allocated in a round-robin manner the generation of the synchronization command Cn starts, the timing of the synchronization command Cn received on the sensor device 10 side will include jitter.

[0056] (Acquisition of count data) When the sensor device 10 acquires (receives) the synchronization command Cn from the acquisition device 12, the number-of-times data acquisition unit 34 acquires the number-of-times data. In the present embodiment, as described above, the counter 21 counts the number of times the count clock signal is received. The number-of-times data acquisition unit 34 acquires, as the number-of-times data, information indicating the number of times the count clock signal is received, which is counted by the counter 21. The number-of-times data acquisition unit 34 may read out the number-of-times data stored in the counter 21 itself from the counter 21, or may read out the number-of-times data stored in the storage unit 24. This number-of-times data acquisition process is performed for each sensor device 10.

[0057] In the present embodiment, it is preferable that the number-of-times data acquisition unit 34 acquires, as the number-of-times data, the number of times the count clock signal is received during the period from the timing when the synchronization command Cn was acquired last time (preferably immediately before) to the timing when the synchronization command Cn is acquired this time. In the present embodiment, when the number-of-times data acquisition unit 34 acquires the number-of-times data, it resets the count of the counter 21. Thereby, each time the number-of-times data is read out (that is, each time the synchronization command Cn is acquired), the number of times the count clock signal is received returns to zero, and the number of times the count clock signal is received during the period from the timing when the synchronization command Cn was acquired last time to the timing when the synchronization command Cn is acquired this time can be acquired as the number-of-times data.

[0058] For example, in FIG. 5, when the sensor device 10A acquires the synchronization command C1 within the period of the time slot TA1, it obtains, as count data, the number of times the count clock signal is received from the timing within the period of the time slot TAn in which the synchronization command was acquired immediately before to the timing within the period of the time slot TA1 in which the synchronization command C1 is acquired this time. Then, the sensor device 10A resets the count of the counter 21 of the sensor device 10A and causes the counter 21 to continue counting. After that, when the sensor device 10A acquires the synchronization command C2 within the period of the time slot TA3, it obtains, as count data, the number of times the count clock signal is received from the timing within the period of the time slot TA1 in which the synchronization command C1 was acquired immediately before to the timing within the period of the time slot TA3 in which the synchronization command C2 is acquired this time, and resets the count of the counter 21. Since the acquisition processing of the count data by the sensor devices 10B, 10C, and 10D is the same, the description thereof is omitted.

[0059] As described above, in the present embodiment, the count data is data indicating the number of times the count clock signal is received until the timing when the sensor device 10 acquires the synchronization command Cn. Here, the count clock signal and the detection clock signal are obtained by dividing the same clock signal. Therefore, it can be said that the frequency of the count clock signal (the number of times the count clock signal is received) corresponds to the frequency of the detection clock signal (the number of times the detection clock signal is received). Therefore, it can also be said that the count data corresponds to the number of times the data is detected by the sensor device 10 until the timing when the sensor device 10 acquires the synchronization command Cn.

[0060] The number data is not limited to the number of times the count clock signal is received, as long as it corresponds to the number of detections of the data up to the timing when the sensor device 10 acquires the synchronization command Cn. For example, the number data may be the number of times the clock signal from the oscillator 20 is received up to the timing when the synchronization command Cn is acquired, or may be the number of times the detection clock signal is received. Also, for example, the number data may be the period or frequency of the count clock signal, the period or frequency of the clock signal, the period or frequency of the detection clock signal, and the like. In this case, for example, the sensor device 10 may calculate the frequency or period of the count clock signal or the like and store it in the storage unit 24 as the number data.

[0061] (Frequency adjustment process) When the number data acquired by the number data acquisition unit 34 of the sensor device 10 does not satisfy a predetermined condition, the frequency adjustment unit 36 of the sensor device 10 changes the frequency of the clock signal output by the oscillator 20. On the other hand, when the number data satisfies the predetermined condition, the frequency adjustment unit 36 does not change the frequency of the clock signal output by the oscillator 20. The predetermined condition here indicates that the degree of deviation between the detection count indicated by the number data and the ideal detection count is sufficiently small. In other words, it means that the degree of deviation between the number data and the reference number data described later is less than a predetermined value. The predetermined value here may be set as appropriate.

[0062] The method of changing the frequency of the clock signal by the frequency adjustment unit 36 may be arbitrary. In this embodiment, when the number data does not satisfy a predetermined condition, the frequency adjustment unit 36 outputs a frequency adjustment command to the analog signal generator 20C. The frequency adjustment command is a digital signal indicating that the frequency is to be adjusted. When the analog signal generator 20C receives the frequency adjustment command, it converts the frequency adjustment command into an analog signal, and the frequency adjustment command converted into the analog signal is input to the frequency adjuster 20B. When the frequency adjuster 20B receives the frequency adjustment command, it adjusts the frequency of the clock signal from the oscillation element 20A to the frequency corresponding to the frequency adjustment command.

[0063] The criterion for determining whether the specified conditions are met may be arbitrary, but an example of the determination method in the present embodiment will be described hereinafter.

[0064] In the present embodiment, the frequency adjustment unit 36 determines whether the count data does not satisfy the specified conditions based on the reference count data and the count data acquired by the count data acquisition unit 34. The reference count data refers to the ideal count data (the count data that should be counted during that period) up to the timing when the synchronization command Cn is acquired. That is, since the count data in the present embodiment is the number of receptions of the counting clock signal during the period from the timing when the synchronization command Cn was acquired in the past to the timing when the synchronization command Cn was acquired this time, the reference count data refers to the ideal number of receptions of the counting clock signal during that period (the number of receptions of the counting clock signal that should be received during that period). The frequency adjustment unit 36 may acquire the reference count data by any method. For example, the reference count data set as a fixed value and stored in the storage unit 24 may be read out. Further, the reference count data may be set to any value. For example, it may be one value or a numerical range having a predetermined numerical width. For example, the reference count data may be a value corresponding to the value obtained by multiplying the period for generating the synchronization command Cn with respect to the reference frequency (the set value of the frequency of the counting clock signal).

[0065] As described above, in the present embodiment, the reference count data is data indicating the ideal number of receptions of the counting clock signal up to the timing when the sensor device 10 acquires the synchronization command Cn. As described above, since the frequency of the counting clock signal (the number of receptions of the counting clock signal) corresponds to the frequency of the detection clock signal (the number of receptions of the detection clock signal), it can also be said that the reference count data is data corresponding to the ideal number of detections of the data by the sensor device 10 up to the timing when the synchronization command Cn is acquired.

[0066] The reference count data is not limited to the ideal detection count of the clock signal for counting, as long as it corresponds to the ideal detection count of the data. For example, the reference count data may be the ideal reception count of the clock signal from the oscillator 20, or the ideal reception count of the clock signal for detection. Also, for example, the reference count data may be the ideal period or frequency of the clock signal for counting, the ideal period or frequency of the clock signal, or the ideal period or frequency of the clock signal for detection.

[0067] (Calculation of adjustment variable) In this embodiment, each time the sensor device 10 acquires a synchronization command, the count data acquisition unit 34 acquires the count data, and the frequency adjustment unit 36 compares the reference count data with the count data to calculate an adjustment variable. The adjustment variable is a value corresponding to the number of times the count data becomes a value different from the reference count data. In this embodiment, the adjustment variable is set to an initial value (zero in this example) before the sensor device 10 first acquires a synchronization command, and the frequency adjustment unit 36 updates the adjustment variable each time it acquires a synchronization command. That is, the frequency adjustment unit 36 changes the adjustment variable every time the count data becomes a value different from the reference count data.

[0068] More specifically, in the present embodiment, when the count data is higher than the reference count data, the frequency adjustment unit 36 changes the adjustment variable by a predetermined number (in this example, 1) to one side (the positive side in this example) of positive and negative. On the other hand, when the count data is lower than the reference count data, the frequency adjustment unit 36 changes the adjustment variable by a predetermined number (in this example, 1) to the other side (the negative side in this example) of positive and negative. Also, when the count data is the same as the reference count data, the adjustment variable is not changed. When the reference count data indicates a numerical range, the frequency adjustment unit 36 changes the adjustment variable to one side when the count data is higher than the upper limit value of the numerical range of the reference count data, changes the adjustment variable to the other side when the count data is lower than the lower limit value of the numerical range of the reference count data, and does not change the adjustment variable when the count data is within the numerical range of the reference count data. The frequency adjustment unit 36 updates the adjustment variable by performing this process each time a synchronization command is acquired. For example, when the initial value of the adjustment variable is 0, the synchronization command is acquired 4 times, and the count data corresponding to those synchronization commands is higher, lower, higher, higher than the reference count data, the adjustment variable is updated in the order of 0, 1, 0, 1, 2.

[0069] By calculating the adjustment variable in this way, it is possible to make an index that appropriately reflects whether the count data (actual detection count) has a tendency to be higher or lower than the reference count data (ideal detection count).

[0070] (Adjustment of Frequency) In the present embodiment, when the adjustment variable is outside a predetermined numerical range, the frequency adjustment unit 36 changes the frequency of the clock signal output by the oscillator 20 on the assumption that the count data does not satisfy a predetermined condition. On the other hand, when the adjustment variable is within a predetermined numerical range, the frequency adjustment unit 36 does not change the frequency of the clock signal on the assumption that the count data satisfies a predetermined condition.

[0071] More specifically, the sensor device 10 repeats the acquisition process of the synchronization command, the acquisition process of the count data, and the update process of the adjustment variable until the number of acquired synchronization commands (cumulative evaluation times) reaches a predetermined threshold. When the number of acquired synchronization commands is less than the threshold, the sensor device 10 does not change the frequency of the clock signal. Then, the sensor device 10 determines whether to change the frequency of the clock signal based on the adjustment variable updated when the number of acquired synchronization commands reaches the threshold. That is, assuming that the adjustment variable updated when the number of acquired synchronization commands reaches a predetermined number of times is the target adjustment variable, the frequency adjustment unit 36 changes the frequency of the clock signal when the target adjustment variable is outside a predetermined numerical range, and does not change the frequency of the clock signal when the target adjustment variable is within the predetermined numerical range. In this way, by determining whether to change the frequency of the clock signal only after the number of synchronization commands (cumulative evaluation times) reaches the threshold or more, it is possible to suppress the frequency from being changed when the count data (in this example, the reception times of the count clock signal) is temporarily shifted. That is, since the frequency can be determined whether to be changed by monitoring the fluctuation of the count data in the long term, the frequency can be adjusted more appropriately. However, this process is not essential, and regardless of the number of acquired synchronization commands, it may be determined whether to change the frequency of the clock signal every time a synchronization command is acquired.

[0072] More specifically, when the target adjustment variable is different from the predetermined reference value on one side (in this example, when it is higher than the reference value), the frequency adjustment unit 36 decreases the frequency of the clock signal. On the other hand, when the target adjustment variable is different from the predetermined reference value on the other side (in this example, when it is lower than the reference value), the frequency adjustment unit 36 increases the frequency of the clock signal. Further, when the target adjustment variable is the same as the predetermined reference value, the frequency adjustment unit 36 does not change the frequency of the clock signal. Here, the reference value is the initial value of the adjustment variable (for example, zero). However, the reference value may be arbitrarily set and is not limited to one value, and may be a numerical range having a predetermined numerical width. When the reference value indicates a numerical range, the frequency adjustment unit 36 decreases the frequency of the clock signal when the target adjustment variable is higher than the upper limit value of the numerical range, increases the frequency of the clock signal when the target adjustment variable is lower than the lower limit value of the numerical range, and does not change the frequency of the clock signal when the target adjustment variable is within the numerical range.

[0073] The above frequency adjustment process is executed for each sensor device 10. By adjusting the frequency of the clock signal of each sensor device 10 in this way, the number of data for each sensor device 10 can be appropriately associated.

[0074] Note that after performing the above frequency adjustment process, the data acquisition system 1 may transmit data from the sensor device 10 to the acquisition device 12 and store the data by the acquisition device 12. That is, first, after associating the number of data for each sensor device 10 by the frequency adjustment process, data may be transmitted from the sensor device 10 to the acquisition device 12 and stored by the acquisition device 12. Further, during the period of detecting data by the sensor device 10, transmitting data from the sensor device 10 to the acquisition device 12, and storing data by the acquisition device 12, the frequency adjustment process may be performed in parallel to sequentially execute the frequency adjustment.

[0075] (Example of Frequency Adjustment) The method of varying the frequency of the clock signal by the frequency adjustment unit 36 may be arbitrary. For example, the frequency of the clock signal may be varied by controlling the output (e.g., voltage) of the circuit provided in the oscillator 20 for controlling the frequency of the clock signal. In this case, it is preferable that the frequency adjustment unit 36 makes the amount of variation of the output of the circuit a constant value regardless of the magnitude of the value of the adjustment variable (target adjustment variable). In other words, when the target adjustment variable is higher than a predetermined reference value, the amount of variation (increase amount) of the output of the circuit is made a constant value regardless of the value of the target adjustment variable, and when the target adjustment variable is lower than the predetermined reference value, the amount of variation (decrease amount) of the output of the circuit is made a constant value regardless of the value of the target adjustment variable. By adjusting the frequency in this way, the desired frequency can be approached without excessively varying the frequency.

[0076] The oscillator 20 is provided with a first circuit (first adjustment unit) for controlling the frequency of the clock signal and a second circuit (second adjustment unit) for controlling the frequency of the clock signal. The frequency adjustment unit 36 may adjust the frequency of the clock signal by adjusting at least one of the outputs of the first circuit and the second circuit. In this case, the ratio of the amount of variation of the frequency of the clock signal to the output variation per unit amount of the second circuit is smaller than the ratio of the amount of variation of the frequency of the clock signal to the output variation per unit amount of the first circuit. The unit amount here refers to the minimum value of the output variation of the circuit. In other words, an output variation less than the unit amount is impossible. That is, the second circuit can be said to be a circuit capable of adjusting the frequency of the clock signal more finely than the first circuit.

[0077] In the example of this embodiment, when providing the first circuit and the second circuit, an analog signal generator 20C corresponding to the first circuit and an analog signal generator 20C corresponding to the second circuit are provided. In this case, the output of the first circuit and the second circuit refers to a frequency adjustment command, which is an analog signal, output from the analog signal generator 20C. That is, in this case, it can be said that the analog signal generator 20C corresponding to the second circuit can adjust the frequency adjustment command, which is an analog signal, more finely than the analog signal generator 20C corresponding to the first circuit. The analog signal generator 20C corresponding to the first circuit may be, for example, a DAC circuit, and the analog signal generator 20C corresponding to the second circuit may be, for example, a PWM circuit.

[0078] FIG. 6 is a graph for explaining an example of frequency adjustment by the first circuit and the second circuit. The horizontal axis in FIG. 6 indicates the output value of the second circuit (second adjustment unit), and the vertical axis indicates the frequency of the clock signal. And the point P1 indicates the frequency of the clock signal when the outputs of the first circuit and the second circuit are predetermined values. In this case, when the output of the first circuit is increased by a unit amount, the frequency of the clock signal discretely increases to the value shown at point P2. Also, when the output of the first circuit is decreased by a unit amount from point P1, the frequency of the clock signal discretely decreases, and the frequency of the clock signal becomes the value shown at point P3. On the other hand, when the output value of the second circuit (second adjustment unit) is varied, the frequency of the clock signal can be continuously varied as indicated by the arrows extending from points P1, P2, and P3.

[0079] In this case, it is preferable that the frequency adjustment unit 36 makes the fluctuation amount of the output of the first circuit a constant value regardless of the magnitude of the value of the adjustment variable (target adjustment variable). For example, when the target adjustment variable is higher than a predetermined reference value, the frequency adjustment unit 36 increases the output of the first circuit by a predetermined amount (for example, a unit amount) regardless of the value of the target adjustment variable. Also, for example, when the target adjustment variable is lower than a predetermined reference value, the frequency adjustment unit 36 decreases the output of the first circuit by a predetermined amount (for example, a unit amount) regardless of the value of the target adjustment variable. Then, the frequency adjustment unit 36 adjusts the output of the second circuit to approach a desired frequency. By adjusting the frequency in this way, it is possible to approach the desired frequency without excessively varying the frequency.

[0080] (Processing flow) The flow of the frequency adjustment process described above will be described. FIG. 7 is a flowchart for explaining the processing flow according to the present embodiment. As shown in FIG. 7, when the sensor device 10 acquires the synchronization command Cn from the acquisition device 12 (step S10), it reads out and stores the count data from the counter 21 from the timing when the synchronization command Cn was acquired immediately before to the timing when the synchronization command Cn was acquired this time (step S12), and resets the count of the counter 21 (step S13). Note that the period at which the synchronization command Cn is transmitted may be, for example, 1 second, and the count data may be, for example, 200,000 times when the sampling frequency is 2000 sps. The sensor device 10 performs the subsequent processing when the number of transmissions of the synchronization command indicated by the synchronization command acquired this time (transmission count information) corresponds to the number of synchronization commands acquired so far stored in the storage unit 24, and does not perform the subsequent processing when they do not correspond. In this example, when the number of transmissions of the synchronization command indicated by the synchronization command is one more than the number of acquisitions of the synchronization command (step S14; Yes), the process proceeds to step S16 and the subsequent processing is performed. On the other hand, when the number of transmissions of the synchronization command is not one more than the number of acquisitions of the synchronization command (step S14; No), the number of acquisitions of the synchronization command to be stored is made to match the number of transmissions of the synchronization command acquired this time, and this process ends. Examples of the case where the number of transmissions of the synchronization command is not one more than the number of acquisitions of the synchronization command include cases where the sensor device 10 cannot receive the synchronization command (for example, the synchronization command is dropped on the wireless path) and the time interval between receptions of the synchronization command is skipped. Since the synchronization command is transmitted with a serial number (identifier for identifying the synchronization command) attached, it is possible to detect whether the number of transmissions of the synchronization command is not one more than the number of acquisitions of the synchronization command by detecting this serial number.

[0081] After step S16, the sensor device 10 updates the adjustment variable based on the count data and the reference count data. The reference count data may be, for example, 200,000 times when the sampling frequency is 2000 sps. Specifically, when the count data is the same value as the reference count data (step S16; Yes), the sensor device 10 holds the adjustment variable without changing it (step S18). On the other hand, when the count data is not the same value as the reference count data (step S16; No) and the count data is higher than the reference count data (step S20; Yes), the sensor device 10 adds 1 to the adjustment variable (step S22). Also, when the count data is lower than the reference count data (step S20; No), the sensor device 10 subtracts 1 from the adjustment variable (step S24).

[0082] After that, if the cumulative number of evaluation times (the number of synchronization commands acquired so far) is not equal to or greater than the threshold value (step S26; No), the number of acquired synchronization commands to be stored is made to match the number of transmitted synchronization commands acquired this time, and this process ends. Note that the cumulative number of evaluation times may be, for example, 60 times. In this case, since the transmission frequency of the synchronization command Cn is 1 second, the frequency adjustment is performed once per minute. On the other hand, if the cumulative number of evaluation times is equal to or greater than the threshold value (step S26; Yes), the cumulative number of evaluation times is reset (step S27), that is, the cumulative number of evaluation times is set back to 0, and the process proceeds to step S28 to perform the adjustment process of the frequency of the clock signal of the oscillator 20. Specifically, when the adjustment variable is the same value as the reference value (step S28; Yes), the sensor device 10 holds the frequency of the clock signal without changing it (step S30). Note that the reference value may be, for example, 0. On the other hand, when the adjustment variable is not the same value as the reference value (step S28; No), and the adjustment variable is higher than the reference value (step S32; Yes), the sensor device 10 decreases the frequency of the clock signal (step S34). Also, when the adjustment variable is lower than the reference value (step S32; No), the sensor device 10 increases the frequency of the clock signal (step S36). For example, when the reference value is 0 and the adjustment variable is +1 or more, a value obtained by subtracting -1 step from the most recent digital signal value (that is, a value obtained by decreasing the output value of the circuit by the unit amount) is instructed, and the frequency is varied by -1 step (the frequency is increased by the unit amount). Also, for example, when the reference value is 0 and the adjustment variable is -1 or less, a value obtained by adding +1 step to the most recent digital signal value (that is, a value obtained by increasing the output value of the circuit by the unit amount) is instructed, and the frequency is varied by +1 step (the frequency is decreased by the unit amount). After performing any of the processes in steps S30 to S34, the adjustment variable is returned to the initial value, the number of acquired synchronization commands to be stored is made to match the number of transmitted synchronization commands acquired this time, and this process ends.

[0083] In this way, in the present embodiment, the frequency is varied by one step (unit amount) regardless of the degree of deviation from the reference value of the adjustment variable. Thereby, the difference in counters caused by an error including the variation in the period of the synchronization command transmitted wirelessly can be averaged. However, the amount of frequency variation is not limited to this, and for example, the amount of frequency variation may be adjusted according to the degree of deviation from the reference value of the adjustment variable. In this case, the sensor device 10 may increase the amount of frequency variation as the degree of deviation from the reference value of the adjustment variable increases. That is, for example, when the difference between the adjustment variable and the reference value is ±2, the amount of frequency variation may be doubled compared to the case where the difference between the adjustment variable and the reference value is ±1. Thereby, since the frequency can be adjusted taking into account the deviation amount of the adjustment variable, a more accurate frequency adjustment can be performed.

[0084] Also, in the present embodiment, as shown in step S26, when the cumulative number of evaluation times reaches a threshold value (for example, 60 times), the frequency adjustment process is executed. However, the trigger for executing the frequency adjustment process is not limited to the cumulative number of evaluation times reaching the threshold value, and the value of the adjustment variable may be used as the trigger for executing the frequency adjustment process. In this case, for example, when the adjustment variable is outside a predetermined range (for example, the range from +1 to -1), the sensor device 10 may execute the frequency adjustment process after step S28.

[0085] (Effect) As described above, the data acquisition system 1 according to the present disclosure includes a plurality of sensor devices 10 and an acquisition device 12. The sensor device 10 includes an oscillator 20 that outputs a clock signal at a predetermined period, a sensor 22 that detects data at a timing based on the clock signal, and a control unit 28. The acquisition device 12 is a device that acquires data detected from a plurality of sensor devices 10, and transmits a synchronization command to the plurality of sensor devices 10 every predetermined period. The control unit 28 includes a count data acquisition unit 34 that acquires count data corresponding to the number of times of data detection until the timing when the synchronization command is acquired, and a frequency adjustment unit 36 that changes the frequency of the clock signal output by the oscillator 20 when the count data does not satisfy a predetermined condition. That is, the sensor device 10 uses the synchronization command transmitted from the acquisition device 12 as a trigger to read out the count data corresponding to the number of times of data detection so far, and determines whether to adjust the frequency according to the count data. Therefore, according to the present embodiment, it is possible to appropriately associate the number of data from each sensor device 10 transmitted to the acquisition device 12.

[0086] Furthermore, in the present embodiment, the frequency of data detection by the sensor 22 is high, and the period of data detection is shorter than the period in which the acquisition device 12 transmits a signal to the sensor device 10. Therefore, in the present embodiment, it is not possible to send a detection command to the sensor device 10 each time, and it is not possible to perform control to perform detection each time the sensor device 10 receives the detection command, and the number of detections cannot be synchronized by a command from the acquisition device 12. Also, in the present embodiment, the communication period (time slot) by the communication module 26 cannot be changed during communication, and synchronization on the communication module 26 side is not possible. Even in such a case, as in the present embodiment, by using the synchronization command transmitted from the acquisition device 12 as a trigger and adjusting the frequency of the clock signal on the sensor device 10 side, it is possible to appropriately associate the number of data from each sensor device 10.

[0087] In addition, the count data acquisition unit 34 acquires, as count data, a value corresponding to the number of times data is detected during the period from the timing when a synchronization command was acquired in the past to the timing when the synchronization command was acquired this time. By acquiring the count data in this way, it is possible to appropriately determine whether adjustment of the frequency of the clock signal is necessary, and it becomes possible to appropriately associate the number of data from each sensor device 10. More specifically, by acquiring the count data during the period from a certain past timing to the current timing, it is possible to obtain count data reflecting the state within a period closer to the present, so it is possible to appropriately determine whether adjustment of the frequency of the clock signal is necessary. Furthermore, by acquiring the count data during the period from the timing when the synchronization command was acquired immediately before to the timing when it was acquired this time, it is possible to reflect the state within an even more recent period, so it is possible to more appropriately determine whether adjustment of the frequency of the clock signal is necessary. However, the period for acquiring the count data is not limited to these. For example, a value corresponding to the number of times data is detected during the period from a predetermined timing (for example, at startup) to the timing when the synchronization command was acquired this time may be acquired as the count data.

[0088] In addition, the frequency adjustment unit 36 determines whether the count data satisfies a predetermined condition based on the reference count data corresponding to the reference number of times data is detected up to the timing when the synchronization command was acquired and the count data. By determining in this way whether frequency adjustment is necessary, it becomes possible to appropriately associate the number of data from each sensor device 10.

[0089] In addition, each time the frequency adjustment unit 36 acquires a synchronization command, it calculates an adjustment variable corresponding to the number of times the count data has become a value different from the reference count data by comparing the reference count data and the count data, and changes the frequency of the clock signal when the adjustment variable is outside a predetermined numerical range. By determining whether to adjust the frequency using the adjustment variable in this way, it becomes possible to appropriately associate the number of data from each sensor device 10.

[0090] Further, when the number-of-times data is higher than the reference number-of-times data, the frequency adjustment unit 36 changes the adjustment variable to one side of positive or negative. When the number-of-times data is less than the reference number-of-times data, the frequency adjustment unit 36 changes the adjustment variable to the other side of positive or negative. By updating the adjustment variable in this way, it becomes possible to appropriately adjust the frequency and appropriately associate the number of data from each sensor device 10.

[0091] Further, when the adjustment variable is a value different from a predetermined reference value on one side, the frequency adjustment unit 36 decreases the frequency of the clock signal. When the adjustment variable is a value different from the reference value on the other side, the frequency adjustment unit 36 increases the frequency of the clock signal. By adjusting the frequency in this way, it becomes possible to appropriately associate the number of data from each sensor device 10.

[0092] Further, the synchronization command includes transmission number information indicating the number of times the synchronization command is transmitted. When the number of synchronization commands acquired so far does not correspond to the number of times the synchronization command is transmitted indicated by the transmission number information, the control unit 28 does not perform the process of changing the frequency of the clock signal. Thereby, it is possible to suppress inappropriate frequency adjustment from being performed inappropriately.

[0093] Further, the acquisition device 12 switches the communication target among a plurality of sensor devices 10 every predetermined period and performs data transmission and reception. The frequency of the clock signal is higher than the communication target switching frequency (time slot switching frequency). According to the present embodiment, in such a case, as described above, it is not possible to send a detection command from the acquisition device 12 to the sensor device 10 each time, and the number of detections cannot be synchronized by a command from the acquisition device 12. On the other hand, according to the present embodiment, even in such a case, it becomes possible to appropriately associate the number of data from each sensor device 10.

[0094] In addition, the acquisition device 12 and the ten sensor devices each have a communication module for transmitting and receiving data. A first time slot in which the communication module of the sensor device 10A (first sensor device) and the communication module of the acquisition device 12 can communicate, and a second time slot in which the communication module of the sensor device 10B (second sensor device) and the communication module of the acquisition device 12 can communicate are fixed and set in this order in time series. In such a case, as described above, synchronization cannot be achieved on the communication module side. In contrast, according to the present embodiment, even in such a case, it is possible to appropriately associate the number of data from each sensor device 10.

[0095] As described above, the embodiments and examples of the present invention have been described, but the embodiments are not limited by the contents of these embodiments and the like. Further, the above-described components include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those within the so-called equivalent range. Furthermore, the above-described components can be combined as appropriate. Still further, various omissions, substitutions, or changes of the components can be made without departing from the gist of the above-described embodiments and the like.

Explanation of Reference Numerals

[0096] 1 Data acquisition system 10 Sensor devices 12 Acquisition device 20 Oscillator 22 Sensor 26 Communication module 34 Number-of-times data acquisition unit 36 Frequency adjustment unit 50 Synchronization command generation unit

Claims

1. A plurality of sensor devices having an oscillator that outputs a clock signal at a predetermined period, a sensor that detects data at a timing based on the clock signal, and a control unit, an acquisition device that acquires the detected data from the plurality of sensor devices, and having, the acquisition device transmits a synchronization command to the plurality of sensor devices every predetermined period, the control unit, a count data acquisition unit that acquires count data which is the number of times of the period from the timing when the synchronization command was acquired in the past to the timing when the synchronization command was acquired this time, and which corresponds to the number of times of detection of the data; a frequency adjustment unit that changes the frequency of the clock signal output by the oscillator when the degree of deviation between the reference count data which is the reference number of times of the period from the timing when the synchronization command was acquired in the past to the timing when the synchronization command was acquired this time and which corresponds to the reference number of times of detection of the data and the count data is equal to or less than a predetermined value; including, a data acquisition system.

2. The frequency adjustment unit, each time the synchronization command is acquired, calculates an adjustment variable corresponding to the number of times the count data has become a value different from the reference count data by comparing the reference count data and the count data, The data acquisition system according to claim 1, wherein when the adjustment variable is outside a predetermined numerical range, the frequency of the clock signal is changed.

3. The frequency adjustment unit changes the adjustment variable to one side of positive or negative when the count data is higher than the reference count data, and changes the adjustment variable to the other side of positive or negative when the count data is less than the reference count data. The data acquisition system according to claim 2.

4. The frequency adjustment unit decreases the frequency of the clock signal when the adjustment variable is a value different from the reference value on one side, and increases the frequency of the clock signal when the adjustment variable is a value different from the reference value on the other side. The data acquisition system according to claim 3.

5. The synchronization command includes transmission count information indicating the number of times the synchronization command is transmitted. If the number of the synchronization commands acquired so far does not match the number of transmissions of the synchronization commands indicated by the transmission count information, the control unit does not perform the process of changing the frequency of the clock signal. The data acquisition system according to any one of claims 1 to 4.

6. A data acquisition method using a plurality of sensor devices each having an oscillator that outputs a clock signal at a predetermined period and a sensor that detects data at a timing based on the clock signal, and an acquisition device that acquires the detected data from the plurality of sensor devices, comprising: transmitting a synchronization command from the acquisition device to the plurality of sensor devices at predetermined intervals; acquiring, from the timing when the sensor device acquired the synchronization command in the past to the timing when the sensor device acquired the synchronization command this time, count data corresponding to the number of detections of the data, which is the count data of the period; changing the frequency of the clock signal output by the oscillator when the degree of deviation between the reference count data of the period from the timing when the synchronization command was acquired in the past to the timing when the synchronization command was acquired this time, which is the reference count data corresponding to the reference number of detections of the data, and the count data is equal to or less than a predetermined value; including a data acquisition method.

7. A program for causing a control unit to execute a data acquisition method using a plurality of sensor devices each having an oscillator that outputs a clock signal at a predetermined period and a sensor that detects data at a timing based on the clock signal, and an acquisition device that acquires the detected data from the plurality of sensor devices, the program causing the control unit to execute: transmitting a synchronization command from the acquisition device to the plurality of sensor devices at predetermined intervals; acquiring, from the timing when the sensor device acquired the synchronization command in the past to the timing when the sensor device acquired the synchronization command this time, count data corresponding to the number of detections of the data, which is the count data of the period; changing the frequency of the clock signal output by the oscillator when the degree of deviation between the reference count data of the period from the timing when the synchronization command was acquired in the past to the timing when the synchronization command was acquired this time, which is the reference count data corresponding to the reference number of detections of the data, and the count data is equal to or less than a predetermined value; causing the control unit to execute. Program.

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