WO2024162337A1

WO2024162337A1 - Control device, control system, method, and program

Info

Publication number: WO2024162337A1
Application number: PCT/JP2024/002831
Authority: WO
Inventors: 太雅新實; 光宏米田
Original assignee: オムロン株式会社
Priority date: 2023-02-01
Filing date: 2024-01-30
Publication date: 2024-08-08
Also published as: JP2024109258A

Abstract

The present invention enables time synchronizations to be promptly and accurately completed. A time synchronization processing unit calculates the time difference between a reference time and the time measured by a timer, and acquires a second threshold that indicates the permissible range of time differences and that is greater than or equal to a first threshold. The time synchronization processing unit carries out either a first correction process to correct the time on the timer using a first correction amount so as to indicate the reference time or a second correction process to correct the time on the timer using a second correction amount that is smaller than the first correction amount. The time synchronization processing unit carries out the first correction process when the time difference is greater than or equal to the second threshold and carries out the second correction process when the time difference is less than the second threshold.

Description

Control device, control system, method and program

This disclosure relates to time synchronization in FA (Factory Automation) control systems.

Control systems using control devices such as PLCs (Programmable Logic Controllers) are becoming common in various production sites. In addition to systems in which one control device controls peripheral devices, distributed control systems have been proposed in which multiple control devices exchange data with each other to collaboratively control peripheral devices. In a distributed control system, it is desirable for the multiple control devices to be time-synchronized with each other in order to work together with high precision.

For example, Patent Document 1 (JP 2019-146060 A) discloses a time synchronization configuration. In this configuration, each of multiple communication devices connected to a network corrects the time of its own device by using the difference between the time of the other communication devices and the time of its own device as a time adjustment value.

JP 2019-146060 A

In FA control systems, a threshold is set that indicates the tolerance range for determining when time synchronization is complete, the time difference described above is compared with this threshold, and the completion of time synchronization is determined based on the result of the comparison. Therefore, depending on the threshold that is set, there have been cases where it takes a long time to complete time synchronization, or time synchronization cannot be performed with high accuracy.

Therefore, the objective of this disclosure is to provide technology that can complete time synchronization quickly and accurately.

The FA (factory automation) control device according to the present disclosure includes a connector for connecting a network, a timer, a control processing unit that performs processing related to the control of the target, and a time synchronization processing unit that performs time synchronization processing.

The time synchronization processing unit includes a time difference calculation unit that calculates the time difference between a reference time and the time measured by the timer, a threshold acquisition unit that acquires a second threshold equal to or greater than a first threshold that indicates an acceptable range of the time difference, and a correction unit that performs either a first correction process that corrects the timer time by a first correction amount so that it indicates the reference time, or a second correction process that corrects the timer time by a second correction amount smaller than the first correction amount so that it indicates the reference time.

The correction unit performs a first correction process when the time difference is equal to or greater than a second threshold, and performs a second correction process when the time difference is less than the second threshold.

According to the control device described above, the correction process is switched between the first correction process and the second correction process based on the relationship between the magnitude of the time difference and a second threshold value that indicates the acceptable range of the time difference and is different from the first threshold value. In this case, if the time difference is equal to or greater than the second threshold value and is relatively far from the acceptable range, the correction unit performs the correction process with the larger first correction amount to quickly reduce the time difference and complete time synchronization. In contrast, if the time difference is less than the second threshold value and close to the acceptable range, the correction unit performs the correction process with the smaller second correction amount to gradually converge the time difference into the acceptable range and complete time synchronization with high precision.

The time on the timer of the control device mentioned above indicates the time based on the clock possessed by the timer, the reference time indicates the time based on the clock of the master device connected to the network, and the time difference calculation unit calculates the time difference based on the difference between the frequency of the timer's clock and the frequency of the master device's clock.

　According to the above-mentioned control device, the time difference used in the time synchronization process is calculated based on the difference between the clock frequency of the control device's timer and the clock frequency of the master device that provides the reference time.

The above-mentioned control device further includes a communication unit that receives a message distributed from a master device connected to the network, and the distributed message from the master device includes the transmission time of the message based on the master clock of the master device. The time difference calculation unit calculates a reference time based on the transmission time of the distributed message received from the master device and the propagation delay time of the network, and calculates the time difference based on the difference between the reception time of the distributed message measured by the timer and the calculated reference time.

The control device described above can calculate the time difference using the reference time included in the message delivered from the master device.

The time synchronization processing unit of the above-mentioned control device determines whether or not the synchronization condition of the time difference being equal to or less than the first threshold is satisfied, and the correction unit, depending on whether or not the synchronization condition is satisfied, performs a first correction process when the time difference is equal to or greater than the second threshold, and performs a second correction process when the time difference is less than the second threshold.

The control device described above can switch between the correction processes described above even when the synchronization conditions are met and it is determined that synchronization is complete, thereby maintaining a time-synchronized state.

The threshold acquisition unit of the control device calculates the second threshold according to a calculation formula using the time difference. This makes it possible to calculate the second threshold using the time difference.

The threshold acquisition unit of the control device calculates the second threshold according to a calculation formula using the magnitude relationship between the first threshold and a predetermined value and the first threshold. This allows the second threshold to be calculated using the magnitude relationship between the first threshold and a predetermined value and the first threshold.

The first correction process of the control device described above repeats the process of correcting the timer time by the first correction amount M times (where M is greater than or equal to 2), and the first correction amount includes a correction amount based on a value obtained by dividing the time difference value into M parts.

In the above-mentioned control device, the first correction process divides the time difference and repeats correction using each divided value, thereby achieving time synchronization.

The second correction process of the control device described above repeats the process of correcting the timer time by the second correction amount N times (where N is greater than or equal to 2), and the second correction amount includes a correction amount based on a value obtained by dividing the time difference value into N parts.

In the above-mentioned control device, the second correction process divides the time difference and repeats correction using each divided value, thereby achieving time synchronization.

The time synchronization processing unit of the above-mentioned control device determines whether or not the synchronization condition of the time difference being equal to or less than a first threshold value is satisfied, and the processing related to the target control includes a first processing that is performed when it is determined that the synchronization condition is satisfied, and a second processing that is different from the first processing and is performed in response to the determination that the synchronization condition is satisfied.

The control device described above can perform different control-related processes depending on whether time synchronization has been completed.

The first process of the control device described above includes a process of collecting data having observed values related to the control of the target and timer times indicating the observed timing.

　According to the control device described above, when the synchronization condition is satisfied and time synchronization is achieved, the first process is executed, making it possible to collect observation values according to the observation time measured by the time-synchronized timer.

In another aspect of this disclosure, there is provided a factory automation (FA) control system that includes a plurality of the control devices described above.

In another aspect of this disclosure, a method is provided that is implemented by a control device of FA (factory automation). The control device includes a connector for connecting a network and a timer. The method includes implementing a process related to the control of an object and implementing a time synchronization process, where implementing the time synchronization process includes calculating a time difference between a reference time and a time measured by the timer, acquiring a second threshold value equal to or greater than a first threshold value indicating an acceptable range of the time difference, and implementing one of a first correction process that corrects the timer time by a first correction amount so as to indicate the reference time or a second correction process that corrects the timer time by a second correction amount smaller than the first correction amount so as to indicate the reference time, and implementing one of such processes includes implementing the first correction process when the time difference is equal to or greater than the second threshold value, and implementing the second correction process when the time difference is less than the second threshold value.

In another aspect of this disclosure, a program is provided for causing a processor of a control device for FA (factory automation) to execute a method. The control device includes a connector for connecting a network and a timer. The method includes executing a process related to the control of an object and executing a time synchronization process, where executing the time synchronization process includes calculating a time difference between a reference time and a time measured by the timer, acquiring a second threshold value equal to or greater than a first threshold value indicating an acceptable range of the time difference, and executing one of a first correction process that corrects the timer time by a first correction amount so as to indicate the reference time or a second correction process that corrects the timer time by a second correction amount smaller than the first correction amount so as to indicate the reference time, and executing one of the processes includes executing the first correction process when the time difference is equal to or greater than the second threshold value, and executing the second correction process when the time difference is less than the second threshold value.

The above program includes instructions that, when executed by a computer, cause the computer to execute the above method.

According to this disclosure, time synchronization can be completed quickly and accurately.

1 is a diagram illustrating an example of an overall configuration of a control system 1 according to an embodiment of the present invention. 2 is a block diagram showing an example of a hardware configuration of a control device 2 according to the present embodiment. FIG. FIG. 5 is a block diagram showing an example of a hardware configuration of a support device 500 according to the present embodiment. 2 is a block diagram showing an example of a software configuration of a control device 2 according to the present embodiment. FIG. FIG. 5 is a diagram illustrating a schematic configuration of a synchronization module 560 according to the present embodiment. 1 is a schematic process flowchart of application design according to the present embodiment. FIG. 7 is a diagram illustrating the application design environment of FIG. 6. FIG. 2 is a diagram showing an example of a communication sequence according to the present embodiment. 4 is a flowchart of a time synchronization process according to the present embodiment. 11 is a diagram illustrating acquisition of a second threshold value according to the present embodiment. FIG. 11 is a diagram illustrating acquisition of a second threshold value according to the present embodiment. FIG. 11 is a diagram illustrating acquisition of a second threshold value according to the present embodiment. FIG. 11 is a diagram illustrating acquisition of a second threshold value according to the present embodiment. FIG. 13 is another flowchart of the time synchronization process according to the embodiment. 10 is a graph illustrating an advantage obtained by variably setting the second threshold value according to the present embodiment. 10 is a graph illustrating an advantage obtained by variably setting the second threshold value according to the present embodiment. 10 is a graph illustrating an advantage obtained by variably setting the second threshold value according to the present embodiment. 10 is a graph illustrating an advantage obtained by variably setting the second threshold value according to the present embodiment. 10 is a graph illustrating an advantage obtained by variably setting the second threshold value according to the present embodiment. 10 is a graph illustrating an advantage obtained by variably setting the second threshold value according to the present embodiment. FIG. 2 is a diagram showing an example of a communication sequence according to the present embodiment. 10 is a graph illustrating a relationship between a time difference and a second threshold value according to the present embodiment.

The embodiment of the present invention will be described in detail with reference to the drawings. Note that the same or corresponding parts in the drawings will be given the same reference numerals and their description will not be repeated.

<A. Application Examples>
First, an example of a situation in which the present invention is applied will be described. In this embodiment, a PLC will be described as a typical example of a "control device", but the technical idea disclosed in this specification is not limited to the name of the PLC and can be applied to any control device.

In addition, in this embodiment, the control device has a management timer that manages time. The control device executes a "time synchronization process" to synchronize the management timer with a reference timer that manages the reference time. The time of the management timer indicates the time based on the clock of the management timer, and the time of the reference timer indicates the time based on the clock of the reference timer.

FIG. 1 is a diagram showing an example of the overall configuration of a control system 1 according to this embodiment.

Referring to FIG. 1, control system 1 realizes factory automation of a production line. More specifically, in control system 1, networks are connected at multiple levels, and different functions are assigned to the networks at each level. Specifically, but not limited to, for example, four levels of networks 11 to 14 are provided.

The control level network 11 is connected to

multiple control devices

2A, 2B, and 2C, a device/line management device 190, and a display device 280 that provides a SCADA (Supervisory Control and Data Acquisition) function, forming a data link that allows data to be exchanged between the devices. When there is no need to distinguish between the

control devices

2A, 2B, and 2C, they are referred to as "control devices 2." The network 11 mainly transmits information related to time synchronization and the control system.

The control device 2 connects one or more field devices 90 via a field-level network 110. These field devices 90 may be directly connected to the control device 2. Each of the one or more field devices 90 includes an actuator that exerts some kind of physical action on a manufacturing device or a production line (hereinafter collectively referred to as the "field"), and an input/output device that exchanges information with the field.

The data exchanged between the control device 2 and the field device 90 via the network 110 is updated at very short intervals of the order of several hundred microseconds to several tens of milliseconds. This process of updating the exchanged data is also called input/output refresh processing.

The management-level network 12 is connected to an equipment/line management device 190 that manages equipment and lines, and

manufacturing management devices

380 and 390 that manage manufacturing plans, etc. The equipment/line management device 190 and

manufacturing management devices

380 and 390 exchange management information such as manufacturing plans, and equipment or line information, via the network 12.

Connected to computer-level network 13 are manufacturing

management devices

380 and 390, and a manufacturing execution system (MES) 400 that manages a time-series DB (short for database) 450.

Manufacturing management devices

380 and 390, and manufacturing execution system 400 exchange production management and information system data via network 13.

The manufacturing execution system 400 stores the observation values, which are input values from the field devices 90 collected via the network 13, in the time series DB 450 as time series data in the order in which they were observed. Specifically, in this embodiment, the control device 2 generates a frame including the specified observation value and data on the time of the management timer, and transfers it to the manufacturing execution system 400 via the

networks

11, 12, and 13.

The manufacturing execution system 400 and external devices on the cloud are connected to the network 14, which includes an external network such as the Internet. The manufacturing execution system 400 transfers data in the time series DB 450 to the devices on the cloud by exchanging data with the devices on the cloud.

In the control system 1 shown in FIG. 1, networks 11-14 and network 110 adopt protocols and frameworks that correspond to the differences in the required characteristics. For example, EtherNet/IP (registered trademark), an industrial open network that implements a control protocol on a general-purpose Ethernet (registered trademark), may be used as the protocol for

networks

11 and 12 belonging to the factory network. Furthermore, EtherCAT (registered trademark), an example of a machine control network, may be used as the protocol for network 110. The same or different protocols may be applied to the protocols for

networks

11 and 110. By adopting such network technology suitable for machine control, real-time performance with a guaranteed time required for transmission between devices can be provided.

In contrast,

networks

13 and 14 belonging to the corporate network use protocols such as general-purpose Ethernet to ensure a diversity of connection destinations. By adopting general-purpose Ethernet, restrictions on the amount of data that can be transmitted can be eliminated.

The control device 2 or the device/line management device 190 may be connected to a support device 500. The support device 500 is a device that assists the control device 2 in making the necessary preparations to control the controlled object.

The control system 1 includes a distributed system 300 in which

control devices

2A, 2B, and 2C are provided in

different processes

3A, 3B, and 3C, respectively. For example, but not limited to, process 3A indicates a part feeder process that aligns and transports workpieces (components, parts), process 3B indicates a process that moves the workpieces aligned in process 3A by a robot's pick-and-place operation, and process 3C indicates a process of assembling the moved workpieces. In the distributed system 300, the operation of the field devices 90 connected to the control device 2 of each process differs from the operation of the field devices 90 connected to the control device 2 of the previous and next processes. In order to meet the required takt time in the distributed system 300, the operation of a certain process is performed in synchronization with the operation of the process before and after the process.

The control device 2 executes control programs, including a sequence program for implementing sequence control of the field devices 90 connected to the control device 2 and a motion program for implementing motion control, at predetermined intervals (also called control intervals) based on synchronized time, thereby achieving real-time control of the field devices 90.

In this disclosure, "time" is intended to indicate a certain point in the flow of time, and is specified using units such as hours, minutes, and seconds. A "timer" basically measures time based on a clock generated by a hardware clock in order to measure values for controlling timing within the control device 2 and related devices. More specifically, the timer may be configured to include a counter that is incremented or decremented by a predetermined value for each predetermined unit time based on the clock frequency. The counter has a predetermined bit length that represents, for example, an integer value. "Synchronization accuracy" can be indicated based on the time difference (error or displacement) between the reference timer and the management timer of the control device 2. Therefore, the smaller the time difference (error or displacement), the higher the "synchronization accuracy", and the larger the time difference (error or displacement), the lower the "synchronization accuracy". A user can set the allowable range of time difference as a "tolerance" so that the desired synchronization accuracy can be achieved in the control system 1. Hereinafter, such a tolerance range is referred to as a "first threshold".

In FIG. 1, the configuration for achieving time synchronization may include, for example, a case where the network 11 performs data communication according to TSN (Time-Sensitive Networking), which is a protocol for industrial networks, and a case where the network 11 performs data communication according to EtherCAT (registered trademark: Ethernet for Control Automation Technology). Note that the standard applied to the network 11 is not limited to these, and may be, for example, IEEE 1588.

Referring to FIG. 1, the master that serves as the "reference timer" transmits a time distribution message 21 including data on the reference time measured by the reference timer to the network 11. The reference timer may be a timer possessed by any of the

control devices

2A, 2B, and 2C, or a timer of another device on the network 11 (e.g., device/line management device 190), and corresponds to the timer with the highest accuracy among these timers. In this embodiment, for example, device/line management device 190 operates as the master.

The support device 500 provides a support tool for designing a synchronization program by executing a support program 590 described later. When designing the control system 1 (or the distributed system 300), the user operates the support tool to design a synchronization application 177 described later. The synchronization application 177 includes a program for implementing time synchronization processing and information on the set first threshold value. The control device 2 realizes time synchronization processing by executing the synchronization application 177 transferred from the support device 500. The user sets the first threshold value by operating the support tool. Note that the method for setting the first threshold value is not limited to user operation, and may be calculated based on the synchronization accuracy required for the control system in the specifications, for example.

In the time synchronization process, the control device 2 acquires a second threshold value equal to or greater than the first threshold value, based on a first threshold value indicating a predetermined tolerance range of the time difference (step ST1). The control device 2 estimates (calculates) the reference time based on the time information contained in the time distribution message 21 received via the network 11, and calculates the time difference between the estimated reference time and the time measured by the management timer (step ST2). Details of the estimation of the reference time and the calculation of the time difference will be described later. The control device 2 performs either a first correction process in which the time of the management timer is corrected by a first correction amount so as to indicate the reference time, or a second correction process in which the time of the management timer is corrected by a second correction amount smaller than the first correction amount so as to indicate the reference time (step ST3). In this correction, when the calculated time difference is greater than the second threshold value, the control device 2 performs the first correction process instead of the second correction process, and when the calculated time difference is equal to or less than the second threshold value, the control device 2 performs the second correction process instead of the first correction process.

The second correction process is a correction process that gradually changes the time on the management timer using a second correction amount that is smaller than the first correction amount used in the first correction process to accurately approach the reference time. In contrast, the first correction process is a correction process that quickly changes the time on the management timer using a first correction amount that is larger than the second correction amount to quickly approach the reference time.

In this way, the control device 2 switches between the second correction process, which gradually changes the time on the management timer to bring it closer to the reference time with high precision, and the first correction process, which quickly changes the time on the management timer to bring it closer to the reference time, depending on the relationship between the magnitude of the value between the time difference and the second threshold value, without relying on the first threshold value for determining whether time synchronization is complete. This allows time synchronization to be completed quickly and accurately.

In this embodiment, the correction of the time difference represents the concept of "adjustment" to add or subtract from the value of the time difference. In this case, the first correction amount or the second correction amount represents the concept of an adjustment amount that represents the amount of addition or subtraction.

A more specific application example of this embodiment will now be described.
<B. Configuration and time synchronization processing>
The configuration of the devices constituting the distributed system 300 will be described. Fig. 2 is a block diagram showing an example of the hardware configuration of the control device 2 according to the present embodiment. Fig. 3 is a block diagram showing an example of the hardware configuration of the support device 500 according to the present embodiment.

(b1. Configuration of control device 2)
Referring to FIG. 2 , the control device 2 includes a processor 102, a chipset 104, a secondary memory device 106, a main memory device 108, a host network controller 105, a Universal Serial Bus (USB) controller 107, a memory card interface 109, a field network controller 118, a counter 126, and a Real Time Clock (RTC) 128.

The processor 102 is composed of a CPU (Central Processing Unit), MPU (Microprocessor unit), GPU (Graphics Processing Unit), etc., and reads out various programs stored in the secondary storage device 106, deploys them in the main storage device 108, and executes them to realize control according to the control target and various processes as described below. The secondary storage device 106 is composed of non-volatile storage devices such as HDD (Hard Disk Drive) and SSD (Solid State Drive). The main storage device 108 is composed of volatile storage devices such as DRAM (Dynamic Random Access Memory) and SRAM (Static Random Access Memory).

The chipset 104 controls the processor 102 and each device to realize processing for the control device 2 as a whole.

The secondary storage device 106 stores communication cycle data 200 indicating the cycle for distributing the time distribution message 21. The secondary storage device 106 stores a UPG (short for user program) 201 that is created according to the manufacturing device or facility to be controlled. The main storage device 108 stores a flag 40 that indicates whether time synchronization is complete or not. For example, the flag 40 is set to "0" as the initial value, and is set to "1" when it is determined that time synchronization is complete.

The upper network controller 105 includes a connector for connecting the network 11 and a circuit such as a NIC (Network Interface Card) having a timer 103. The upper network controller 105 exchanges data with the manufacturing execution system 400 or a device on the cloud (see FIG. 1) via the upper network 11. The USB controller 107 controls the exchange of data with the support device 500 via a USB connection.

The memory card interface 109 is configured to allow the memory card 116 to be attached and detached, and is capable of writing data to the memory card 116 and reading various data (such as user programs or trace data) from the memory card 116.

The counter 126 is used as a time reference for managing the execution timing of various processes in the control device 2. The counter 126 constitutes a clock that can be a "management timer" or a "reference timer". The counter 126 has a clock and provides time based on the clock. Typically, the counter 126 generates a clock and increments or decrements the counter value for each clock period. The count value of the counter 126 represents the time measured by the timer. The counter 126 may be implemented using a hardware timer such as a High Precision Event Timer (HPET) arranged on the system bus that drives the processor 102, or may be implemented using a dedicated circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array). The control device 2 synchronizes the

timers

103, 119, 91A, and 91B with the counter 126.

The RTC 128 is a type of counter with a timekeeping function, and provides the current time to the processor 102 etc.

The field network controller 118 controls data exchange with other devices, including the field device 90, via the network 110. The field network controller 118 has a connector that connects to the network 110, and a timer 119 that is used as a time reference for managing timing with other devices. In FIG. 4, the timers 91 of the field device 90 are indicated by

timers

91A, 91B, etc.

The timer 119 and the counters (

timers

91A and 91B) of devices such as the field device 90 can have a configuration similar to that of the counter 126 described above. The timer 119 is synchronized with the counter 126.

The field network controller 118 functions as a communication master for periodic communication via the network 110, and continuously monitors the difference between the counter value indicated by the counter of each device connected to the field bus and the counter value indicated by the timer 119, and outputs a synchronization signal to instruct a device in which a discrepancy in the counter value occurs to make a correction, if necessary. In this way, the field network controller 118 has a synchronization management function that issues a command to the device to make the counter value indicated by the device's counter match the counter value indicated by the timer 119.

FIG. 2 shows an example of a configuration in which the necessary functions are provided by the processor 102 executing a program, but some or all of these provided functions may be implemented using dedicated hardware circuits (e.g., an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array)). Alternatively, the main part of the control device 2 may be realized using hardware that follows a general-purpose architecture (e.g., an industrial PC based on a general-purpose PC). In this case, virtualization technology may be used to run multiple OSs (Operating Systems) with different uses in parallel, and necessary applications may be executed on each OS.

In the control system 1 according to this embodiment, the control device 2 and the support device 500 are configured as separate entities, but a configuration in which all or part of these functions are integrated into a single device may also be adopted.

(b2. Configuration of Support Device 500)
3, the support device 500 corresponds to an information processing device such as a computer. The support device 500 includes portable and stationary information processing devices. The support device 500 includes a CPU (Central Processing Unit) 501, a memory 502 configured as a volatile storage device such as a DRAM (Dynamic Random Access Memory), a timer 503, a hard disk 504 configured as a non-volatile storage device such as a HDD, an input interface 505, a display controller 506, a communication interface 507, and a data reader/writer 508. These components are connected to each other via a bus 509 so as to be able to communicate data with each other.

The input interface 505 mediates data transmission between the CPU 501 and input devices such as a keyboard 510, a mouse (not shown), and a touch panel (not shown). The display controller 506 is connected to a display 511 and displays the results of processing by the CPU 501. The communication interface 507 communicates with the control device 2 or the device/line management device 190 via USB. The data reader/writer 508 mediates data transmission between the CPU 501 and a memory card 512, which is an external storage medium.

Note that memory card 116 in FIG. 2 and memory card 512 in FIG. 3 include volatile or non-volatile storage media, such as general-purpose semiconductor storage devices such as CF (Compact Flash: registered trademark) and SD (Secure Digital), magnetic storage media such as flexible disks, or optical storage media such as CD-ROMs (Compact Disk Read Only Memory).

Hard disk 504 stores various programs and data, including support program 590, transfer program 595, and GUI (Graphical User Interface) program 550. When executed, transfer program 595 transfers UPG 201 and data designed in support device 500 to control device 2. GUI program 550 provides an interface for the user to operate tools provided by executing support program 590 or transfer program 595.

(b3. Software configuration example of control device 2)
Next, an example of the software configuration of the control device 2 constituting the control system 1 according to the present embodiment will be described.

FIG. 4 is a block diagram showing an example of the software configuration of the control device 2 according to this embodiment. Referring to FIG. 4, the control device 2 includes an execution engine 150, a time series database 180, a higher-level connection program 192, and a gateway program 194.

The execution engine 150 constitutes a type of program that executes various programs in an execution environment for the various programs. Typically, this execution environment is provided by the processor 102 of the control device 2 reading out a system program stored in the secondary storage device 106, expanding it into the main storage device 108, and executing it.

More specifically, the execution engine 150 includes a control program 152 for implementing control-related processing related to the control of the field device 90, a variable management program 160, a scheduler program 170 for managing the execution order of the programs, an input program 172, and an output program 174. The execution engine 150 further includes a synchronization application 177 for implementing time synchronization processing. The control device 2 includes a gateway program 194 and an upper connection program 192 for implementing various processing including service processing related to control.

The control program 152 is typically connected to a database writing program 156 and a serialized communication program 158. When executed, the control program 152 corresponds to the main part that performs the control calculation process, and the control program 152 can be arbitrarily configured according to the manufacturing device or facility that is the object of control by the control device 2.

The database writing program 156 is called by an instruction defined in the control program 152, and writes specified data to the time series database 180. The serialization communication program 158 performs serialization processing on the data written to the time series database 180 by the database writing program 156. The gateway program 194 communicates with devices on the cloud. For example, it provides time series data 182 of the time series database 180 to a device that provides an IoT service on the cloud. The database writing program 156, the serialization communication program 158, and the gateway program 194 may be optional.

The variable management program 160 manages values available to the execution engine 150 in the form of variables. More specifically, the variable management program 160 manages system variables indicating the state of the control device 2, device variables indicating values held by various devices such as the field equipment 90 connected to the control device 2, and user variables indicating values held by the control program 152 executed by the control device 2.

The input program 172 provides a function for acquiring input data from field devices 90, including devices such as actuators and sensors connected to the control device 2. The output program 174 outputs command values (output data) calculated by the control program 152 executed in the control device 2 to the field devices 90, which are the target devices connected via the network 110. In this embodiment, the synchronization application 177 for time synchronization processing includes various information such as a correction program 178 that corrects the time of the management timer of the control device 2.

When the scheduler program 170 is executed, it provides a scheduler. The scheduler manages resource allocation, including the processor 102, and execution timing for processes or tasks of the control device 2 according to the execution priority assigned to the process or task. Such processes or tasks include processes or tasks that can be generated by the control device 2 executing the control program 152, variable management program 160, input program 172, output program 174, and synchronization application 177, etc.

The time series database 180 is typically placed in the main storage device 108 or the secondary storage device 106, and has a function for storing data as well as a search function for responding to an external request (query) with specified data. The time series database 180 stores time series data 182 written by the database writing program 156. In other words, the time series database 180 stores at least a portion of the input data, output data, calculation data calculated in the control calculation by the control program 152, manufacturing data, and event data in chronological order.

The upper connection program 192 exchanges data with external devices connected to the upper network 13, such as the manufacturing execution system 400. In the control device 2 according to this embodiment, input data and calculation data are output from the control device 2 to the manufacturing execution system 400, and manufacturing information can be received from the manufacturing execution system 400.

In this embodiment, the manufacturing execution system 400 has the time series DB 450 of FIG. 1. In this case, instead of the upper connection program 192 or as part of the upper connection program 192, a database connection program 193 (database is indicated as "DB" in the figure) can be provided. By executing the database connection program 193, the time series data 182 of the time series database 180 in the control device 2 can be transferred to the manufacturing execution system 400 and stored in the time series DB 450.

The variable management program 160 manages, as variables, the input data (status values) that the input program 172 acquires from the field and the manufacturing data that the upper connection program 192 acquires from the manufacturing execution system 400. The control program 152 executes a pre-specified control operation while referencing the system variables, device variables, and user variables managed by the variable management program 160, and outputs the execution results (output data) to the variable management program 160. The control system 1 or the control device 2 can collect such status values or output data as "observation values" of the field.

(b4. Configuration of Synchronization Module)
Fig. 5 is a diagram illustrating a schematic configuration of a synchronization module 560 according to the present embodiment. The synchronization module 560 illustrated in Fig. 5 is provided by executing the synchronization application 177 in Fig. 5. Referring to Fig. 5, the synchronization module 560 includes a threshold acquisition module 521, a correction module 522, and a time difference calculation module 523. In the synchronization module 560, these modules may be configured as a single module.

The threshold acquisition module 521 acquires a second threshold indicating a value equal to or greater than a first threshold, based on a first threshold indicating a predetermined acceptable range of the time difference. The time difference calculation module 523 calculates the time difference between the reference time and the time of the management timer. The correction module 522 performs either a first correction process for correcting the time of the counter 126 by a first correction amount so that it indicates the reference time, or a second correction process for correcting the time of the counter 126 by a second correction amount smaller than the first correction amount so that it indicates the reference time. More specifically, the correction module 522 compares the calculated time difference with the second threshold, and performs the first correction process when it determines based on the result of the comparison that the time difference is greater than the second threshold, and performs the second correction process when it determines that the time difference is equal to or less than the second threshold.

C. Time Synchronization Applications
FIG. 6 is a schematic process flow chart of application design according to this embodiment. FIG. 7 is a diagram showing the application design environment of FIG. 6. The support device 500 executes a support program 590 to execute a process for supporting the application design of FIG. 6, and executes a GUI program 550 to display the UI screen 51 of FIG. 7 on the display 511. The UI screen 51 of FIG. 7 includes

windows

51A, 51B, and 51C that display objects configured to be able to accept user operations. The window 51A includes a button 51D that accepts a user operation to specify whether or not to start the synchronization application 177 in the control device 2 and execute the time synchronization process by valid or invalid. The button 51D of FIG. 7 indicates that, for example, "valid" has been specified.

Window 51B includes a text box 51E that accepts a user operation for setting the first threshold of the control device 2. For example, 500 μs (microseconds) is set in text box 51E. Window 51C is an area that accepts a user operation for editing the control program 152. The program in window 51C shows a control structure that judges whether time synchronization has been completed based on flag 40, and executes one of process A and process B based on the judgment result. A program that expresses such a control structure is referred to below as "control structure program 51F". When transfer program 595 of support device 500 is executed, the information set on UI screen 51 is transferred to the control device 2.

In this embodiment, the control program 152 is designed according to the specifications of a predetermined programming language. The programming language can typically be written using any language defined in the international standard IEC 61131-3, such as LD (Ladder Diagram), IL (Instruction List), ST (Structured Text), FBD (Function Block Diagram), or SFC (Sequential Function Chart).

Referring to FIG. 6, the support device 500 accepts a setting for enabling or disabling time synchronization processing and a setting for a first threshold value based on user operations in

windows

51A and 51B (step S1). The support device 500 accepts a control structure program 51F based on user operations in window 51C (step S2). The support device 500 transfers the information accepted in step S1 and the control structure program 51F to the control device 2 (step S3). In the control device 2, the control structure program 51F transferred from the support device 500 is executed in synchronization with the control period according to a schedule managed by the scheduler program 170.

When the control device 2 determines that the execution of the time synchronization process is set to "enabled" based on the information received from the support device 500, it starts the time synchronization process from step S4 onwards (step S4). When the control device 2 completes time synchronization through the time synchronization process, it sets flag 40 to "1". When time synchronization is not completed, flag 40 indicates "0".

The control device 2 executes the control structure program 51F in parallel with the time synchronization process. In executing the control structure program 51F, the control device 2 executes process B instead of process A while it determines that time synchronization is not complete based on the flag 40 (step S5), and executes process A instead of process B when it determines that time synchronization is complete based on the flag 40 (step S6) (step S7). Details of process A and process B will be described later.

<D. Obtaining the time difference>
In this embodiment, the scheduler of the control device 2 manages the priority of the execution of tasks or processes. More specifically, the highest priority is assigned to the process or task of the control-related process including the processing of the control structure program 51F, and the low priority is assigned to the process or task of the time synchronization process and the service process. The scheduler assigns the processor 102 to the control-related process with the highest priority in the control period, and when the execution of the control-related process is completed, assigns the processor 102 to the process with the low priority in the remaining "slack time". This ensures that the control-related process is executed within the control period in each control device 2, and data exchanged between the control devices 2 is transmitted preferentially to the network 11, ensuring the arrival time of the data. In this embodiment, the time synchronization process is mainly executed in the "slack time" of the control period.

(d1. Communication sequence for obtaining time difference)
In the control system 1, for time synchronization, a high-precision time synchronization protocol such as IEEE1588, IEEE802.1AS, or IEEE802.1AS-Rev can be adopted. As a high-precision time synchronization protocol, for example, IEEE1588 specifies gPTP (generalized Precision Time Protocol). gPTP can be applied to a communication system including a master, which is a reference timer, and a slave, which is a timer synchronized with the reference timer. In gPTP, frames having a time distribution message 21 are periodically exchanged between the master and the slave, and the slave's time is corrected to match the master's reference time based on information such as the time difference obtained in the process. In this embodiment, the control device 2 can correct the time using either a time difference calculated based on a frequency difference, which is the difference between the clock frequency of the reference timer and the clock frequency of the management timer (hereinafter referred to as a frequency-based time difference), or a time difference calculated based on a timestamp of the reference time indicated by the time distribution message 21 (hereinafter referred to as a message-based time difference).

The frequency-based time difference will be explained with reference to FIG. 8. FIG. 8 is a diagram showing an example of a communication sequence according to this embodiment. FIG. 8 shows a communication sequence according to gPTP, for example. In this communication sequence, the master M and the slave S work together to realize communication for time synchronization between the master and the slave. To simplify the explanation, the master M communicates with the slave S without going through a repeater.

In FIG. 8, the slave S (control device 2) receives a message (Sync) periodically distributed from a master device connected to the network. The message (Sync) includes the transmission time of the message based on the clock of the master device. The slave S, as a time difference calculation module 523, (i) for each periodically distributed message (Sync), (i-1) calculates a first time measured by the management timer and indicating when the message (Sync) was received, (i-2) calculates a second time measured by the clock of the master device and indicating when the master device transmitted the distributed message based on the transmission time of the message (Sync) and the propagation delay time of the network, (ii) for the message (Sync) and a message (Sync) delivered one cycle after the delivery of the message, (ii-1) calculates the difference between the frequency of the clock of the master device and the frequency of the clock of the management timer from the difference in the first time between the two messages and the difference in the second time between the two messages, and (ii-2) calculates a frequency-based time difference based on the calculated frequency difference and the above cycle.

More specifically, the slave S receives a time-distributed message (Sync) from the master M at least twice (at times T1 and T2). The slave S saves (stores) the Sync reception time and the Sync estimated reception time for each message (Sync). The Sync reception time is the time measured by the management timer and indicates the time when the slave S received the message (Sync), while the Sync estimated reception time is the time estimated to have been measured by the reference timer of the master M and indicates the time when the slave S received the message (Sync). The slave S calculates the Sync estimated reception time according to the gPTP stack. This calculation is based on the message timestamp and the propagation delay time of the message on the network, as shown in FIG. 21, which will be described later.

The slave S also calculates the Sync reception period. The slave S calculates the time difference with the master M until the next message (Sync) is received. For example, the time difference calculation module 523 calculates (estimates) the time difference according to the formula (time difference = frequency difference × Sync reception period).

Slave S calculates the frequency difference according to the formula ((Tref_d - Tlocal_d) / (Tlocal_d)). Tref_d is calculated according to (Tref - Trev_prev), and Tlocal_d is calculated according to (Tlocal - Tlocal_prev). Here, Tref indicates the estimated reference time when slave S receives the second message (Sync), and Tlocal indicates the time measured by slave S's management timer when slave S receives the second message (Sync). Furthermore, Tref_prev indicates the estimated reference time when slave S receives the first message (Sync), and Tlocal_prev indicates the time measured by slave S's management timer when slave S receives the first message (Sync).

According to the calculation shown in FIG. 8, for example, if the management time of slave S advances by 20 seconds and advances by 25 seconds on the time axis of master M, the frequency difference is calculated to be 0.25. Next, when the management time of slave S advances by 20 seconds, the time difference between that management time and the reference time of master M is calculated to be 0.25 x 20 seconds = 5 seconds in terms of the management time of slave S. In this way, the frequency-based time difference indicates the time difference that occurs in part due to the clock frequency difference between the reference timer and the management timer during the communication cycle of the time distribution message 21.

Next, the message-based time difference will be explained with reference to FIG. 21. FIG. 21 is a diagram showing an example of a communication sequence according to this embodiment. FIG. 21 shows a gPTP communication sequence. In this communication sequence, for simplicity of explanation, the master M also communicates with the slave S without going through a repeater.

In FIG. 21, a slave S (control device 2) receives a message distributed from a master M connected to the network. Such a distributed message includes the transmission time of the message based on the clock possessed by the master M. The slave S, as a time difference calculation module 523, calculates a reference time based on the transmission time of the message received from the master M and the message propagation delay time of the network, and calculates a message-based time difference based on the difference between the reception time of the message measured by the management timer and the calculated reference time.

More specifically, the slave S calculates (estimates) the message-based time difference based on the timestamp (time) obtained from the gPTP time distribution message 21 exchanged with the master M. First, the master M transfers the message (Sync) and the message (FollowUp) to the slave S. The message (FollowUp) indicates the transmission time t1 of the message (Sync) measured by the reference timer of the master M. In order to obtain the propagation delay time of the message (frame), the slave S transmits a message (Pdelay_Req) to the master M at time t3, and then receives a message (Pdelay_Resp) in response to the message (Pdelay_Req) from the master M, and subsequently receives the message (Pdelay_Resp_FollowUp). The message (Pdelay_Resp) indicates the time t4 measured by the reference timer when the master M received the message (Pdelay_Req), and the message (Pdelay_Resp_FollowUp) indicates the time t5 measured by the reference timer when the master M sent the message (Pdelay_Resp). The slave S calculates the above-mentioned propagation delay time td by (td = ((t6-t3)-(t5-t4))/2) based on the time t2 and time t6 when the message was received and the timestamps indicated by each message received from the master M. The slave S estimates the time measured by the master M's reference timer when the slave S's management timer received the message (Sync), that is, the reference time (t1+td), and calculates (estimates) the time difference according to (t2-(t1+td)). By implementing the communication sequence of FIG. 21, the slave S can estimate the master M's reference time and estimate the message-based time difference from the estimated reference time.

In this embodiment, the "time synchronization process" includes a process of estimating the reference time and the time difference by implementing the communication sequence of FIG. 8 or FIG. 21. The time synchronization process is implemented in synchronization with a communication cycle. The "communication cycle" refers to a cycle for transmitting a synchronization message (message (sync)) between the master M and the slave S via the network 11. More specifically, the communication cycle refers to a cycle in which the master M transmits a message (Sync) to the slave S, or a cycle in which the slave S receives a message (Sync) from the master M. The scheduler of each control device 2 allocates the processor 102 to a process that follows the communication sequence in synchronization with such a communication cycle.

The time synchronization protocol in this embodiment is not limited to gPTP or PTP, and other wired or wireless communication protocols can be applied. For example, NTP (Network Time Protocol) or SNTP (Simple Network Time Protocol), GPS (Global Positioning System) or Synchronous Ethernet (registered trademark) protocols, CS-NMS (Clock-sampling mutual network synchronization), RBS (Reference Broadcast Synchronization) and RBIS (Reference Broadcast Infrastructure Synchronization) protocols can also be applied.

<E. Correction Processing>
In this embodiment, the control device 2 performs a phase correction corresponding to the first correction process or a frequency correction corresponding to the second correction process as a correction to align the management time with the reference time. The time difference handled in such a correction process is a frequency-based time difference or a message-based time difference, and indicates a positive or negative value.

(e1. Phase correction and frequency correction)
The correction process will be described with the detected time difference described above as time difference D. In phase correction, the time difference D is treated as a first correction amount, and the control device 2 adds the time difference to the time of the management timer, thereby quickly matching the management timer to the reference timer. In contrast, in frequency correction, the control device 2 adjusts the increment value per increment of the counter constituting the management timer with a second correction amount based on the magnitude of the time difference D described above, thereby gradually decreasing the time difference and matching the management timer to the reference timer. For example, the increment value is calculated based on the time difference D according to a calculation formula for PID (Proportional-Integral-Differential) control.

Alternatively, for example, the control device 2 may divide the time difference D into N (N≧2) values, and periodically add or subtract (increment or decrement) each of the divided values Di (i=1, 2, 3, ... N) to the time value measured by the management timer by a value corresponding to the second correction amount. In this way, the addition or subtraction is repeated N times, allowing the time on the management timer to change gradually (smoothly).

Furthermore, the first correction amount used in the first correction process is not limited to the time difference D. For example, the control device 2 may divide the time difference D into M (M>N≧2) values and periodically add or subtract (increment or decrement) each of the divided values Dj (j=1, 2, 3, ... M) to the time value measured by the management timer. In this way, in the first correction process, the addition or subtraction of a value that is the first correction amount larger than the second correction amount is repeated M times, thereby changing the time on the management timer.

The values of N and M or the values Di and Dj may be variable. For example, these values may be variable based on the magnitude of the time difference D. The period of addition or subtraction using the value Di or Dj may be synchronized with the control period. In this case, the control system 1 can be gradually transitioned to a time synchronization completion state over N or M control periods. In this embodiment, the second correction amount is set to a value smaller than the first correction amount, so that the first correction process can quickly converge the control system 1 to a time synchronization completion state, and the second correction process can gradually bring the control system 1 closer to the time synchronization completion state, allowing for accurate convergence.

<F. Flowchart of time synchronization process>
A case where phase correction or frequency correction is performed in the time synchronization process performed by the control device 2 will be described. Fig. 9 is a flowchart of the time synchronization process according to this embodiment. Referring to Fig. 9, when the control device 2 is started, it determines whether the time synchronization process is valid based on the information received from the support device 500 (step S10). If it is determined that the time synchronization process is not valid (NO in step S10), the process ends, but if it is determined that the time synchronization process is valid (YES in step S10), the process proceeds to step S11.

The control device 2 acquires a first threshold value from the information received from the support device 500 (step S11) and calculates the time difference (step S13). More specifically, the control device 2 determines whether the time distribution message 21 has been received two or more times (step S12). If it is determined that the time distribution message 21 has not been received two or more times (NO in step S12), the control device 2 repeats step S12, but if it is determined that the time distribution message 21 has been received two or more times (YES in step S12), the control device 2 calculates the time difference (step S13). In step S13, for example, a frequency-based time difference is calculated. The control device 2 acquires and sets a second threshold value indicating a value equal to or greater than the first threshold value (steps S14, S15). The acquisition of the second threshold value will be described in detail later.

The control device 2 activates the correction module 522 to start time correction (step S16).

The control device 2 determines whether to receive the time distribution message 21 (step S17). While it is determined that the time distribution message 21 has not been received (NO in step S17), step S17 is repeated, but when it is determined that the time distribution message 21 has been received (YES in step S17), the time difference is calculated (step S18). In step S18, for example, the frequency-based time difference and the message-based time difference are calculated.

The control device 2 compares the frequency-based time difference calculated in step S18 with a first threshold value, and determines, based on the result of the comparison, whether the condition that the frequency-based time difference is less than or equal to the first threshold value continues to be satisfied for a certain period of time (step S19). In steps S18 and S19, the control device 2 calculates the frequency-based time difference for each of the times periodically output by the management timer, and determines whether the period during which the above condition is satisfied for each time difference calculated in this way continues for a certain period of time.

If it is determined that the state in which the above conditions are satisfied has continued for a certain period of time (YES in step S19), the control device 2 sets flag 40 to "1" to indicate that time synchronization has been completed (step S20), and proceeds to step S21. On the other hand, if it is determined that the state in which the above conditions are satisfied has not continued for a certain period of time (NO in step S19), the control device 2 proceeds to step S21 without executing the processing in step S20.

In step S21, the control device 2 compares a representative time difference of the multiple frequency-based time differences calculated in steps S18 and S19 with a second threshold value, and determines whether the representative time difference is equal to or greater than the second threshold value based on the comparison result (step S21). This representative time difference includes the average value, mode, median, latest value, etc. of the multiple frequency-based time differences calculated in steps S18 and S19.

The control device 2 determines whether the representative time difference is equal to or greater than the second threshold, and performs correction processing using the message-based time difference calculated in steps S18 and S19 based on the determination result. More specifically, if the control device 2 determines that the representative time difference is equal to or greater than the second threshold (YES in step S21), it performs phase correction processing (step S22), and if the control device 2 determines that the representative time difference is not equal to or greater than the second threshold, i.e., is less than the second threshold (NO in step S21), it performs frequency correction processing (step S23). Then, it returns to step S17.

9, when the control device 2 determines that time synchronization is complete (YES in step S19), it always determines that the time difference is equal to or less than the second threshold (NO in step S21) and performs frequency correction (step S23). In this way, when time synchronization is complete in the control device 2 (YES in step S19), even if a correction process is performed, frequency correction is performed and phase correction is not performed, so that "time backtracking" of the management timer does not occur. In this embodiment, when the time of the management timer is ahead of the reference time, if a phase correction process is performed to add the time difference to the time of the management timer, the time of the management timer may go back to an earlier time because the fluctuation amount of the time of the management timer is large. Such a case is called "time backtracking". In the frequency correction process, the time of the management timer is corrected to gradually reduce the time difference, so that the management timer can be converged to a time synchronization completion state with high accuracy without causing "time backtracking", and it is possible to maintain the time synchronization completion state thereafter.

(f1. Obtaining the second threshold)
10 to 13 are diagrams for explaining how the second threshold value is obtained according to the present embodiment. The mechanism for obtaining the second threshold value in steps S14 and S15 will be explained.

First, the threshold acquisition module 521 includes a first calculation module that calculates the second threshold according to a calculation formula using the frequency-based time difference, for example. In step S14 of FIG. 9, the control device 2 acquires the second threshold using the frequency-based time difference calculated in step S13 by the first calculation module. More specifically, the control device 2 calculates the second threshold according to the formula (second threshold = time difference x A). However, the coefficient A satisfies the condition (A > 1). For example, the second threshold calculated when A = 1 requires the condition (A > 1) to avoid the condition of step S21 being satisfied and phase correction being repeated. In addition, the second threshold is required to satisfy the condition (second threshold ≦ upper limit value X) to prevent an extreme value from being set. In addition, the condition (second threshold ≧ first threshold) is required to be satisfied to prevent "time backtracking". The values A and X are set based on experiments, etc.

FIG. 14 is another flowchart of the time synchronization process according to the present embodiment. In FIG. 14, steps S12 and S13 are omitted from the flowchart in FIG. 9, but the other steps are the same as in FIG. 9 and therefore will not be described again. In step S14 in FIG. 14, the control device 2 obtains a second threshold value based on a first threshold value set by the user.

The threshold acquisition module 521 includes a second calculation module that acquires the relationship between the magnitude of the first threshold and a predetermined value, and calculates the second threshold according to the relationship and a calculation formula using the first threshold. For example, the control device 2 sets the second threshold differently when the relationship is acquired that the first threshold is less than a predetermined value and when the relationship is acquired that the first threshold is equal to or greater than the predetermined value. For example, the first threshold is set in the window 51B of FIG. 12. As shown in the process of FIG. 13, when the first threshold is less than 1 ms (millisecond), the control device 2 sets the second threshold to 1 ms, and when the first threshold is 1 ms or less, sets the second threshold to a value of (first threshold x 2). With this setting method, it is possible to avoid a case where the second threshold becomes too small compared to the first threshold, causing repeated phase correction. In addition, in order to prevent the second threshold from becoming an extreme value, it is required to satisfy the condition (second threshold ≦ upper limit value X).

As another method, instead of the calculation by the first calculation module or the second calculation module, the threshold acquisition module 521 may be configured to acquire the second threshold using a look up table (LUT). More specifically, the control device 2 acquires a value selected by the user from among the multiple values in the window 51B of the UI screen in FIG. 10 as the first threshold, and the control device 2 searches the table 44 in FIG. 11 for the second threshold based on the first threshold. The table 44 is stored in advance in the control device 2. In the table 44, multiple records representing combinations of the first threshold and the second threshold are registered. The combinations of the first threshold and the second threshold are acquired by experiments or the like. For example, when the first threshold is selected in the window 51B, the second threshold of the record R1 is searched for in the table 44 in FIG. 11. Note that the second threshold in the table 44 satisfies the condition that it is at least equal to or greater than the first threshold and the condition of the upper limit value X described above.

FIG. 22 is a graph showing a schematic relationship between the time difference and the second threshold in this embodiment. The vertical axis of this graph shows the time difference value, and the horizontal axis shows the elapsed time. The time difference described in FIG. 22 shows the frequency-based time difference or the message-based time difference. The time difference D3 shows the time difference obtained to calculate (estimate) the second threshold in step S14. FIG. 22 shows the second threshold shown by a dashed line and

graphs

221 and 222. The second threshold shown by a dashed line shows the value calculated (estimated) by the control device 2 in step S14 according to (second threshold = time difference D3 x A, where A = 5). Graph 221 shows the change in the second threshold when based on the time difference D3 obtained to calculate (estimate) the second threshold in step S14, that is, the change in the value calculated by the formula (D3 x A (where A is changed to 1, 2, 3, 4, 5)). Additionally, graph 222 represents the change in the time difference calculated (estimated) by the control device 2 in step S18 in synchronization with the period SY.

In FIG. 22, at time T1 immediately after the phase correction, the time difference is 0 (zero), and the control timer of the control device 2 is synchronized with the reference timer. In this state, the time difference D3 should be smaller than the second threshold, so the control device 2 performs frequency correction for a period TT (time T2 to time T7) that corresponds to the length of several cycles SY immediately after the phase correction. In other words, during the period TT from when the time difference is 0 (zero) immediately after the phase correction until the next phase correction is performed, multiple frequency corrections can be performed. By performing such frequency corrections, the speed at which the time difference shown in graph 222 increases becomes slower as time passes. After the period TT has elapsed, the control device 2 determines that the time difference has exceeded the second threshold indicated by the dashed line, and performs phase correction in accordance with this determination.

Furthermore, assuming a case in which the second threshold is set to (second threshold = time difference D3 x A, where A = 1) unlike the case in FIG. 22, in that case, there is a possibility that the time difference will exceed the second threshold at time T2 when a message (Sync) is received immediately after phase correction is performed at time T1. Therefore, the control device 2 performs phase correction at time T2. In such a case, since phase correction is performed repeatedly, there is a high possibility that "time regression" will occur and the time difference may not converge.

<G. Specific Cases>
In this embodiment, the control device 2 sets the second threshold based on the frequency-based time difference. In this case, the control device 2 changes the second threshold according to the magnitude of the frequency-based time difference, and can change the second threshold for switching between phase correction and frequency correction according to the first threshold or the magnitude of the frequency-based time difference.

Figures 15 to 20 are graphs that explain the advantages of setting the second threshold to a variable value according to this embodiment. Figures 15, 16, and 17 show cases where the second threshold is fixed, unlike this embodiment. In these cases, since the second threshold is a fixed value, it takes time to complete time synchronization due to the magnitude of the second threshold or the relationship between the magnitude of the first threshold and the second threshold. In Figure 15, the second threshold is too large compared to the first threshold, so the message-based time difference remains large even after phase correction is performed, but frequency correction is started in such a state, so it takes a long time to complete time synchronization. In Figure 16, the second threshold is too small, so only phase correction is repeatedly performed even when the message-based time difference is small, and as a result, it takes a long time to complete time synchronization. In Figure 17, since the second threshold has a relationship of (second threshold < first threshold), phase correction is performed even during time synchronization after time synchronization is completed. As a result, there is a high possibility that "time backwards" will occur.

In contrast, Figs. 18, 19, and 20 show cases in which the second threshold is not fixed but is changed according to the magnitude of the frequency-time difference. Fig. 18 shows a case in which the second threshold is set based on the frequency-based time difference in the case of Fig. 15. More specifically, in Fig. 18, a value that is not too large compared to the first threshold is set for the second threshold, so that phase correction and frequency correction can be combined and implemented, and the time required to complete time synchronization can be shortened compared to the case of Fig. 15. Fig. 19 shows a case in which the second threshold is set based on the frequency-based time difference in the case of Fig. 16. More specifically, in Fig. 19, a value that is not too large and not too small compared to the first threshold is set for the second threshold, so that phase correction and frequency correction can be combined and implemented, and the time required to complete time synchronization can be shortened compared to the case of Fig. 15 or Fig. 16. Fig. 20 shows a case in which the second threshold is set based on the frequency-based time difference in the case of Fig. 17. More specifically, in FIG. 20, the second threshold is set to have the relationship (first threshold = second threshold), which makes it possible to prevent "time going backwards" as shown in FIG. 17.

<H. Example of Processing of Control Structure Program>
When the control structure program 51F is executed, the control device 2 performs control-related processing. For example, this control-related processing includes processing in which the control device 2 issues a query to the manufacturing execution system 400 in order to store the data in the time-series DB 450. This query follows a database manipulation language (SQL: Structured Query Language) in order to store data in a time series. The data includes the observed values collected by the control device 2 and the management time as a timestamp associated with each observed value. When time synchronization is completed in each control device 2, the timestamps from each control device 2 indicate the time synchronized with each other. Therefore, the manufacturing execution system 400 can aggregate (i.e., integrate) the time-series data of the observed values from each control device 2 in the time-series DB 450 by matching the observed timing based on the timestamp. Using the data aggregated in this way makes it easier to analyze the observed values.

In contrast, if time synchronization has not been completed in the control device 2, the time stamps of each control device 2 will not be synchronized, and even if the manufacturing execution system 400 aggregates the time series data of observed values in the time series DB 450, it will not be possible to analyze the aggregated data based on the observation time.

Process A of the control structure program 51F includes a process that is performed when time synchronization is complete. More specifically, in process A, the control device 2 generates time series data having a timestamp and an observation value of the time output by the management timer, and transmits it to the manufacturing execution system 400. Process B includes a process that is performed when time synchronization is not complete. More specifically, in process B, the control device 2 does not execute process A. Alternatively, in process B, the control device 2 generates time series data having a timestamp, an observation value, and an identifier of "time synchronization not complete", and transmits it to the manufacturing execution system 400.

In this way, by the control device 2 referring to the flag 40 set in the time synchronization process when executing the control structure program 51F, it is possible to differentiate the control-related process that is performed when time synchronization is incomplete as described above from the control-related process that is performed when time synchronization is complete. Note that the processes A and B that are performed based on the flag 40 are not limited to the transfer of observed values to the manufacturing execution system 400 described above.

In the time synchronization process described above, the second threshold was set based on the frequency-based time difference, but the second threshold may also be set based on the message-based time difference. Also, the correction amount used in the time correction process described above is set based on the message-based time difference, but the correction amount may also be set based on the frequency-based time difference. Note that this method of setting does not limit gPTP time correction to time correction using the frequency-based time difference.

<I. Program>
The processor 102 of the control device 2 executes the programs in the secondary storage device 106 to realize the time synchronization process and the control-related processes or methods described above.

The programs and data executed to realize these processes may be downloaded from an external device to the secondary storage device 106. More specifically, they are downloaded from the memory card 116 via the memory card interface 109, or downloaded from an external device connected to the network via the upper network controller 105.

The CPU 501 of the support device 500 provides the support tool to the user. The hard disk 504 may store programs and data for implementing the support tool. The programs and data for implementing the support tool may be downloaded to the hard disk 504 via the communication interface 507 and various communication lines. Alternatively, they may be downloaded to the hard disk 504 via the memory card 512.

Memory card 116 or memory card 512 is a medium that stores information such as a program through electrical, magnetic, optical, mechanical, or chemical action so that the information can be read by a computer or other device or machine.

<J. Notes>
The present embodiment as described above includes the following technical idea.
[Configuration 1]
A control device (2) for FA (factory automation),
A connector (105) for connecting to a network (11);
A timer (126);
A control processing unit (152) that performs processing related to the control of the target;
A time synchronization processing unit (560) that performs a time synchronization process;
The time synchronization processing unit
A time difference calculation unit (523) that calculates a time difference between a reference time and a time measured by the timer;
a threshold acquisition unit (521) that acquires a second threshold that is equal to or greater than a first threshold indicating an allowable range of the time difference;
a correction unit (522) that performs one of a first correction process (S22) that corrects the time of the timer by a first correction amount so that the time indicates the reference time, and a second correction process (S23) that corrects the time of the timer by a second correction amount smaller than the first correction amount so that the time indicates the reference time,
The correction unit is
A control device that performs the first correction process when the time difference is equal to or greater than the second threshold value, and performs the second correction process when the time difference is less than the second threshold value.
[Configuration 2]
the time of the timer indicates a time based on a clock included in the timer,
the reference time indicates a time based on a clock of a master device connected to the network,
2. The control device according to configuration 1, wherein the time difference calculation unit calculates the time difference based on a difference between a clock frequency of the timer and a clock frequency of the master device.
[Configuration 3]
The control device further includes a communication unit for receiving a message (21) delivered from a master device connected to the network,
a broadcast message from the master device including a transmission time of the message based on a master clock of the master device;
The time difference calculation unit
Calculating the reference time based on the transmission time of the delivery message received from the master device and a propagation delay time of the network;
3. The control device according to

configuration

1 or 2, wherein the time difference is calculated based on a difference between a reception time of the delivery message measured by the timer and the calculated reference time.
[Configuration 4]
The time synchronization processing unit
determining whether a synchronization condition is satisfied, that is, the time difference is equal to or smaller than the first threshold value;
A control device described in any one of configurations 1 to 3, wherein the correction unit performs the first correction process when the time difference is greater than or equal to the second threshold value, and performs the second correction process when the time difference is less than the second threshold value, depending on whether the synchronization condition is satisfied.
[Configuration 5]
The threshold acquisition unit
The control device according to any one of configurations 1 to 4, wherein the control device calculates the second threshold value according to a calculation formula using the time difference.
[Configuration 6]
The threshold acquisition unit
The control device according to any one of configurations 1 to 5, wherein the second threshold value is calculated according to a calculation formula using a magnitude relationship between the first threshold value and a predetermined value and the first threshold value.
[Configuration 7]
The first correction process includes:
Repeating the process of correcting the time of the timer by the first correction amount M times (where M≧2);
The control device according to any one of configurations 1 to 6, wherein the first correction amount includes a correction amount based on a value obtained by dividing the value of the time difference into M parts.
[Configuration 8]
The second correction process includes:
Repeating the process of correcting the time of the timer by the second correction amount N times (N≧2);
The control device according to any one of configurations 1 to 7, wherein the second correction amount includes a correction amount based on a value obtained by dividing the value of the time difference by N.
[Configuration 9]
The time synchronization processing unit determines whether or not a synchronization condition that the time difference is equal to or less than the first threshold is satisfied;
The control device according to any one of configurations 1 to 8, wherein the processing related to the control of the target includes a first processing that is performed when it is determined that the synchronization condition is satisfied, and a second processing that is performed in response to it being determined that the synchronization condition is satisfied and is different from the first processing.
[Configuration 10]
10. The control device of configuration 9, wherein the first process includes a process of collecting data having observed values related to control of the object and times of the timer indicative of observed timing.
[Configuration 11]
A factory automation (FA) control system comprising a plurality of control devices according to any one of configurations 1 to 10.
[Configuration 12]
A method implemented by a control device (2) of a factory automation (FA), comprising:
The control device includes a connector (105) for connecting to a network (11) and a timer (126);
The method comprises:
performing a process related to the control of the target; and performing a process of time synchronization;
The execution of the time synchronization process includes:
Calculating a time difference between a reference time and a time measured by the timer;
obtaining a second threshold value that is equal to or greater than the first threshold value and indicates an acceptable range of the time difference;
performing one of a first correction process for correcting the time of the timer by a first correction amount so as to indicate the reference time, and a second correction process for correcting the time of the timer by a second correction amount smaller than the first correction amount so as to indicate the reference time;
The implementation of one of the above
performing the first correction process when the time difference is equal to or greater than the second threshold, and performing the second correction process when the time difference is less than the second threshold.
[Configuration 13]
A program (177) for causing a processor (102) of a control device (2) for FA (factory automation) to execute a method,
The control device includes a connector (105) for connecting to a network (11) and a timer (126);
The method comprises:
performing a process related to the control of the target; and performing a process of time synchronization;
The execution of the time synchronization process includes:
Calculating a time difference between a reference time and a time measured by the timer;
obtaining a second threshold value that is equal to or greater than the first threshold value and indicates an acceptable range of the time difference;
performing one of a first correction process for correcting the time of the timer by a first correction amount so as to indicate the reference time, and a second correction process for correcting the time of the timer by a second correction amount smaller than the first correction amount so as to indicate the reference time;
The implementation of one of the above
The program includes: performing the first correction process when the time difference is equal to or greater than the second threshold; and performing the second correction process when the time difference is less than the second threshold.

The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

1 Control system 2, 2A, 2B, 2C Control device 3A, 3B, 3C Process 11, 12, 13, 14, 110 Network 21 Time distribution message 40 Flag 44 Table 51 Screen 51A, 51B, 51C Window 51D Button 51E Text box 51F Control structure program 90 Field equipment 91, 91A, 91B, 103, 119, 503 Timer 102 Processor 104 chip set, 105 upper network controller, 106 secondary storage device, 107 controller, 108 main storage device, 109 memory card interface, 116, 512 memory card, 118 field network controller, 126 counter, 150 execution engine, 152 control program, 156 database writing program, 158 serialized communication program, 160 variable management management program, 170 scheduler program, 172 input program, 174 output program, 177 synchronization application, 178 correction program, 180 time series database, 182 time series data, 190 line management device, 192 upper connection program, 193 database connection program, 194 gateway program, 200 communication cycle data, 280 display device, 300 distributed system, 380 manufacturing management device, 400 manufacturing execution system, 500 support device, 502 memory, 504 hard disk, 505 input interface, 506 display controller, 507 communication interface, 510 keyboard, 511 display, 521 threshold acquisition module, 522 correction module, 523 time difference calculation module, 560 synchronization module, 590 support program, 595 transfer program.

Claims

A control device for FA (factory automation),
A connector for connecting a network;
A timer;
A control processing unit that performs processing related to the control of the target;
A time synchronization processing unit that performs a time synchronization process,
The time synchronization processing unit
a time difference calculation unit that calculates a time difference between a reference time and a time measured by the timer;
a threshold acquisition unit that acquires a second threshold that is equal to or greater than a first threshold and indicates an allowable range of the time difference;
a correction unit that performs one of a first correction process that corrects the time of the timer by a first correction amount so that the time of the timer indicates the reference time, and a second correction process that corrects the time of the timer by a second correction amount smaller than the first correction amount so that the time of the timer indicates the reference time,
The correction unit is
A control device that performs the first correction process when the time difference is equal to or greater than the second threshold value, and performs the second correction process when the time difference is less than the second threshold value.
the time of the timer indicates a time based on a clock included in the timer,
the reference time indicates a time based on a clock of a master device connected to the network,
The control device according to claim 1 , wherein the time difference calculation unit calculates the time difference based on a difference between a clock frequency of the timer and a clock frequency of the master device.
The control device further includes a communication unit that receives a message delivered from a master device connected to the network,
a broadcast message from the master device including a transmission time of the message based on a master clock of the master device;
The time difference calculation unit
Calculating the reference time based on the transmission time of the delivery message received from the master device and a propagation delay time of the network;
The control device according to claim 1 , wherein the time difference is calculated based on a difference between a reception time of the distribution message measured by the timer and the calculated reference time.
The time synchronization processing unit
determining whether a synchronization condition is satisfied, that is, the time difference is equal to or smaller than the first threshold value;
A control device as described in any one of claims 1 to 3, wherein the correction unit performs the first correction process when the time difference is greater than or equal to the second threshold value, and performs the second correction process when the time difference is less than the second threshold value, depending on whether the synchronization condition is satisfied.
The threshold acquisition unit
The control device according to claim 1 , wherein the second threshold value is calculated according to a calculation formula that uses the time difference.
The threshold acquisition unit
The control device according to any one of claims 1 to 3, wherein the second threshold value is calculated according to a calculation formula using a magnitude relationship between the first threshold value and a predetermined value and the first threshold value.
The first correction process includes:
Repeating the process of correcting the time of the timer by the first correction amount M times (where M≧2);
4. The control device according to claim 1, wherein the first correction amount includes a correction amount based on a value obtained by dividing the value of the time difference into M parts.
The second correction process includes:
Repeating the process of correcting the time of the timer by the second correction amount N times (N≧2);
4. The control device according to claim 1, wherein the second correction amount includes a correction amount based on a value obtained by dividing the value of the time difference by N.
The time synchronization processing unit determines whether or not a synchronization condition that the time difference is equal to or less than the first threshold is satisfied;
The control device according to any one of claims 1 to 3, wherein the processing related to the control of the target includes a first processing that is performed when it is determined that the synchronization condition is satisfied, and a second processing that is performed in response to it being determined that the synchronization condition is satisfied and is different from the first processing.
The control device according to claim 9, wherein the first process includes a process of collecting data having an observed value related to the control of the object and a time of the timer indicating the observed timing.
A factory automation (FA) control system comprising a plurality of control devices according to any one of claims 1 to 3.
A method implemented by a control device of a factory automation (FA), comprising:
The control device includes a connector for connecting a network and a timer;
The method comprises:
performing a process related to the control of the target; and performing a process of time synchronization;
The execution of the time synchronization process includes:
Calculating a time difference between a reference time and a time measured by the timer;
obtaining a second threshold value that is equal to or greater than the first threshold value and indicates an acceptable range of the time difference;
performing one of a first correction process for correcting the time of the timer by a first correction amount so as to indicate the reference time, and a second correction process for correcting the time of the timer by a second correction amount smaller than the first correction amount so as to indicate the reference time;
The implementation of one of the above
performing the first correction process when the time difference is equal to or greater than the second threshold, and performing the second correction process when the time difference is less than the second threshold.
A program for causing a processor of a control device for FA (factory automation) to execute a method,
The control device includes a connector for connecting a network and a timer,
The method comprises:
performing a process related to the control of the target; and performing a process of time synchronization;
The execution of the time synchronization process includes:
Calculating a time difference between a reference time and a time measured by the timer;
obtaining a second threshold value that is equal to or greater than the first threshold value and indicates an acceptable range of the time difference;
performing one of a first correction process for correcting the time of the timer by a first correction amount so as to indicate the reference time, and a second correction process for correcting the time of the timer by a second correction amount smaller than the first correction amount so as to indicate the reference time;
The implementation of one of the above
The program includes: performing the first correction process when the time difference is equal to or greater than the second threshold; and performing the second correction process when the time difference is less than the second threshold.