Time synchronization system

Abstract

If the communication delay time is long, the time drift of the clock function is suppressed by shortening the transmission interval of time synchronization packets. [Solution] The time synchronization system comprises a first communication device as the source of synchronization and a second communication device as the destination for synchronization. The second communication device comprises a first communication means for receiving time synchronization packets from the first communication device, a calculation means for calculating a communication delay time using the transmission time and reception time of the time synchronization packets, and an adjustment means for adjusting the time of the clock function of the second communication device using a time correction amount based on the communication delay time. If the communication delay time is longer than a threshold, the first communication means sends a first message to the first communication device to shorten the transmission interval of the time synchronization packets.

Description

[[Technical Field]]

[0001] The present invention relates to a time synchronization system, a communication device, a processing method for a time synchronization system, a processing method for a communication device, and a program. [[Background Art]]

[0002] In recent years, the technology of operating a system in synchronization between a plurality of devices has been used in various fields. One example is a technology called volumetric video, which generates an image of a three-dimensional model using synchronously captured images from a plurality of cameras, and creates a three-dimensional image viewable from any viewpoint.

[0003] In order to synchronize imaging timing among a plurality of cameras, a technology in which the cameras perform time synchronization through network communication is used. As a technology for achieving time synchronization between network communication devices, PTP Version 2 (Precision Time Protocol Version 2) defined in the IEEE1588-2008 standard is known. PTP is a communication protocol for time adjustment via communication. PTP, by performing communication between a time distribution server device called GMC (Grand Master Clock) (synchronization source) and a client device (synchronization destination), can continuously synchronize the time of the synchronization destination to the time of the synchronization source with high accuracy.

[0004] When PTP time synchronization is performed via a wireless LAN, it may be affected by collision avoidance mechanisms for communication data, such as CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance), potentially resulting in random delays in transmission after the necessary packet transmission timestamps are stamped. Furthermore, PTP packet loss may occur due to the wireless environment and other wireless communication devices, such as radio wave reflection, attenuation, and interference, potentially leading to PTP packet retransmission. These PTP packet transmission delays and retransmissions generate jitter in the PTP communication delay. Since PTP assumes that the communication delay time between the synchronization source and destination is constant in both directions, communication delay jitter in wireless communication can degrade the accuracy of time synchronization between the synchronization source and destination.

[0005] Patent Document 1 discloses a technology that involves performing a time synchronization sequence defined by PTP multiple times, calculating the minimum communication delay time from among them, and then performing time correction based on the minimum communication delay time after a predetermined number of executions. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2014-165582 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the method of performing the time synchronization sequence described in Patent Document 1 a predetermined number of times requires the exchange of messages a predetermined number of times at predetermined synchronization intervals in order to perform a single time synchronization. There was a concern that the time difference between the synchronization source and the synchronization destination would widen until the predetermined number of message exchanges were completed. [Means for solving the problem]

[0008] The time synchronization system comprises a first communication device as the source of synchronization and a second communication device as the destination for synchronization. The second communication device includes a first communication means for receiving time synchronization packets from the first communication device, a calculation means for calculating a communication delay time using the transmission time and reception time of the time synchronization packets, and an adjustment means for adjusting the time of the clock function of the second communication device using a time correction amount based on the communication delay time. If the communication delay time is longer than a threshold, the first communication means sends a first message to the first communication device to shorten the transmission interval of the time synchronization packets. [Effects of the Invention]

[0009] According to the present invention, when the communication delay time is long, the time drift of the clock function can be suppressed by shortening the transmission interval of time synchronization packets. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows an example configuration of a synchronized imaging system. [Figure 2] This diagram shows an example of a receiver camera configuration. [Figure 3] This is a flowchart showing the initial camera setup. [Figure 4] This is a diagram showing the time synchronization sequence. [Figure 5] This is a flowchart illustrating the synchronization process in a receiver camera. [Figure 6] This is a flowchart showing the synchronization process in a sender camera. [Modes for carrying out the invention]

[0011] (First Embodiment) A first embodiment of the present invention is described below.

[0012] Figure 1 shows an example configuration of the synchronous shooting system 100 according to the first embodiment. The synchronous shooting system 100 shows that the sender camera 101 and receiver cameras 102a to 102f perform synchronous shooting of the target 103. The sender camera 101 and receiver cameras 102a to 102f (hereinafter collectively referred to as "each camera" as the cameras constituting the synchronous shooting system 100) synchronize their time via a network.

[0013] The above network is a wireless LAN compliant with the IEEE standard, Wi-Fi (registered trademark, hereinafter omitted), but it may also be configured in combination with wired LANs, industrial Ethernet, etc. Furthermore, it is not limited to these, and other types of networks may also be used.

[0014] Furthermore, in this embodiment, the IEEE standard-compliant PTP (Precision Time Protocol) is used for time synchronization, but other synchronization protocols such as NTP (Network Time Protocol) may also be used.

[0015] Each camera is designed to take consecutive shots at the same time (shooting timing) within the system. This will be defined as synchronized shooting from now on.

[0016] The photographer controls each camera by operating the sender camera 101 at any time. Synchronized shooting starts when the photographer selects it, for example, using a button or GUI not shown in this embodiment, and ends when the photographer deselects it, sending a stop command.

[0017] Synchronized shooting may be performed automatically when each camera is started up, without requiring any operation from the photographer. In this case, for example, synchronized shooting is terminated when a cancellation instruction is given via a button or GUI (not specified in this embodiment), or when a stop instruction is given during a shutdown sequence (not specified in this embodiment).

[0018] The sender camera 101 is a camera that distributes operation details to the receiver cameras 102a to 102f in accordance with the photographer's operations. In the present embodiment, the sender camera 101 and the receiver cameras 102a to 102f are the same type of camera, and are called differently according to their roles. Note that the sender camera 101 and the receiver cameras 102a to 102f may each be different types of cameras. Further, each camera may be a communication device such as a smartphone or a PC.

[0019] In the present embodiment, the initial settings are configured as the sender camera 101 or the receiver cameras 102a to 102f. Based on this setting, the receiver cameras 102a to 102f operate as cameras that perform imaging based on the operation details distributed from the sender camera 101.

[0020] Hereinafter, when collectively referring to the receiver cameras 102a to 102f, they are referred to as "receiver camera 102".

[0021] The imaging target 103 is a target to be imaged by each of the cameras.

[0022] Figure 2 is a block diagram showing an example of the internal configuration and connections of the receiver camera 102a illustrated in Figure 1. Each camera is configured with respective functional blocks (a communication unit 210, a control unit 220, a temporary storage unit 230, a synchronization signal generation counter 240, an imaging control unit 250, a recording unit 260, an imaging unit 270, and a shutter button 280), and is controlled by the control unit 220. Unless otherwise specified, the receiver cameras 102b to 102f and the sender camera 101 also have the same configuration.

[0023] Each functional block is mutually connected via a system bus. The receiver camera 102a is communicatively connected to the sender camera 101 and the other receiver cameras 102. Note that each camera may be connected to the sender camera 101 via a device serving as a communication master such as an AP (Access Point).

[0024] The communication unit 210 is a wireless communication interface that communicates with each of the other cameras. The wireless communication interface consists of a MAC and a PHY. The communication unit 210 has a communication function 211 and a clock function 212. The communication unit 210 is also connected to a synchronization signal generation counter 240 via a control line 213, and periodically transmits the time from the clock function 212. The communication unit 210 may also support communication using communication methods other than Wi-Fi, such as 5G or Bluetooth.

[0025] The communication function 211 is a communication protocol function that forms a communication path with the sender camera 101 and other receiver cameras 102 and sends and receives communication packets. Examples of communication packets include time synchronization packets that synchronize the time of each camera, and control signals.

[0026] The clock function 212 is a function that measures the synchronized time on each camera. The time of the clock function 212 is transmitted and received by a time synchronization sequence defined by a time synchronization protocol (PTP in this embodiment). At this time, the sender camera 101 is the synchronization source and the receiver camera 102 is the synchronization destination. Details of the time synchronization sequence are explained in Figure 4. The clock function 212 is also connected to the synchronization signal generation counter 240 via a control line 213 and periodically transmits its own time to the synchronization signal generation counter 240. It is also possible that there is a GM (Grand Master) device in the synchronized shooting system 100 that has a highly accurate time and transmits the time. In such a case, the sender camera 101 may have the function of a synchronization destination and be set to receive the time from the GM device and synchronize the clock function 212 with the time of the GM device.

[0027] Control line 213 is a control line that notifies the synchronization signal generation counter 240 of the value of the clock function 212.

[0028] The control unit 220 is a CPU that controls each functional block. The control functions of the control unit 220 include executing time synchronization sequences, decoding packets received by the communication unit 210, and executing the operating system. The control unit 220 also has a function to determine whether to operate as a sender camera 101 or a receiver camera 102 at startup.

[0029] The temporary storage unit 230 is a memory that stores information necessary for the control unit 220 to control each functional block, and is mainly composed of semiconductor memory such as DRAM (Dynamic Random Access Memory). The temporary storage unit 230 stores various types of information handled by each functional block 210 to 280.

[0030] The synchronization signal generation counter 240 is a counter that generates the shooting timing that forms the basis of synchronized shooting for the shooting control unit 250. Examples of shooting timing include PPS (Pulse Per Second) signals with precise intervals and ratios, which are transmitted to the shooting control unit 250 via the notification line 290. PPS is a square wave transmitted at a constant period. The synchronization signal generation counter 240 counts based on the time of the clock function 212, which is periodically notified via the control line 213. This enables the synchronization signal generation counter 240 to generate shooting timing synchronized with the time of the clock function 212.

[0031] The imaging control unit 250 is the part that drives the imaging unit 270 to perform imaging based on the imaging timing from the synchronization signal generation counter 240. The imaging control unit 250 is directly connected to the synchronization signal generation counter 240 via the notification line 290, and drives the imaging unit 270 when it receives the imaging timing from the notification line 290.

[0032] The sender camera 101 and the receiver camera 102 are controlled to perform synchronized shooting based on the time displayed on the clock function 212 of the sender camera 101 and the time displayed on the clock function 212 of the receiver camera 102, respectively.

[0033] The recording unit 260 is an auxiliary storage device for recording images and is mainly composed of flash memory such as a memory card or SSD. The recording unit 260 may be located within the temporary storage unit 230 or connected to other devices via the communication unit 210.

[0034] The imaging unit 270 is a sensor that receives control from the imaging control unit 250 and performs imaging. Specifically, the imaging unit 270 may use a CMOS sensor, a CCD sensor, or the like.

[0035] The shutter button 280 is a button pressed by the photographer operating the sender camera 101. The shutter button 280 is not used on the receiver camera 102 and therefore does not need to be present. The photographer determines the timing of the shot by pressing the shutter button 280 on the sender camera 101. Note that the shutter button 280 is not limited to a physical button, such as a button on the UI displayed on the touch panel display.

[0036] Notification line 290 is a notification line through which the synchronization signal generation counter 240 notifies the shooting control unit 250 of the shooting timing.

[0037] Figure 3 is a flowchart of the common initial settings performed by each camera in the synchronized shooting system 100 shown in Figure 1. The control unit 220 performs various processes by executing programs stored in the recording unit 260 or the temporary storage unit 230.

[0038] Step S310 indicates the starting point of the flowchart. Step S310 shows that each camera has been activated as one of the terminals constituting the synchronized shooting system 100 shown in Figure 1.

[0039] In step S320, the control unit 220 for each camera sets the role of each camera. The control unit 220 determines whether each camera will behave as a sender camera 101 or a receiver camera 102, which is the role required for each camera to perform synchronized shooting in the synchronized shooting system 100 shown in Figure 1. The control unit 220 determines whether to behave as a sender camera 101 or a receiver camera 102 according to the initial values ​​of settings and parameters that are stored in advance in the temporary storage unit 230.

[0040] In step S330, the control unit 220 of each camera initializes the temporary storage unit 230. The control unit 220 initializes the information written to the temporary storage unit 230 so that synchronization can begin. During initialization, the threshold values ​​described in Figure 5 are set.

[0041] In step S340, the control unit 220 of each camera performs the process of establishing a communication path between the cameras in order to form the synchronized shooting system 100 shown in Figure 1. The control unit 220 of each camera exchanges information necessary for synchronized shooting using a predetermined communication protocol via the communication unit 210.

[0042] Step S350 marks the end of the flowchart. This flow ensures that each camera establishes a communication connection with the other cameras, completes time synchronization, and outputs the shooting timing at a synchronized interval based on the synchronized time.

[0043] Figure 4 shows the time synchronization sequence executed in the synchronized imaging system 100 shown in Figure 1. This sequence is executed one-to-one with the sender camera 101 as the synchronization source and each of the receiver cameras 102 as the synchronization destination. Alternatively, the system may be configured so that the sender camera 101 is the synchronization destination and the receiver camera 102 or an external GM device is the synchronization source.

[0044] In step S410, the sender camera 101 first sends a Sync packet, which is a time synchronization packet, at time T1. The receiver camera 102 receives the Sync packet at time T2. A Sync packet is a type of PTP packet.

[0045] In step S411, if the sender camera 101's synchronization process is operating in 2Step mode, it sends a Follow Up packet, which is a time synchronization packet. Here, the Follow Up packet contains the time T1. The Sync packet and Follow Up packet sent from the sender camera 101 are transmitted via multicast. The receiver camera 102 receives the Follow Up packet. The Follow Up packet is a type of PTP packet.

[0046] In step S412, the receiver camera 102, having received the Sync packet and Follow Up packet, performs the synchronization process and, at time T3, sends a Delay Request packet, which is a time synchronization packet, to the sender camera 101. The sender camera 101 receives the Delay Request packet at time T4. The Delay Request packet is a type of PTP packet.

[0047] In step S413, the sender camera 101, having received the Delay Request packet, sends a Delay Response packet, which is a time synchronization packet, to the receiver camera 102. Here, the Delay Response packet contains the time T4. The receiver camera 102 receives the Delay Response packet. The Delay Response packet is a type of PTP packet.

[0048] Here, time T1 indicates the time in the clock function 212 when the communication unit 210 of the sender camera 101 sent the Sync packet. Time T2 indicates the time in the clock function 212 when the communication unit 210 of the receiver camera 102 received the Sync packet. Time T3 indicates the time in the clock function 212 when the communication unit 210 of the receiver camera 102 sent the Delay Request packet. Time T4 indicates the time in the clock function 212 when the communication unit 210 of the sender camera 101 received the Delay Request packet. Time T1 is stored in the Follow Up packet, and time T4 is stored in the Delay Response packet.

[0049] Furthermore, the reception time T2 of the Sync packet and the transmission time T3 of the Delay Request packet can be obtained by the following procedure. The control unit 220 of the receiver camera 102 latches the clock function 212 when the communication unit 210 receives the Sync packet. This allows the control unit 220 to obtain the time T2.

[0050] Similarly, with respect to time T3, the control unit 220 of the receiver camera 102 latches the clock function 212 at the timing when a Delay Request packet is sent from the communication unit 210 to the sender camera 101. This allows the control unit 220 to obtain time T3.

[0051] By executing the above time synchronization sequence, the receiver camera 102 can obtain four time points T1 to T4. From these four time points, the communication delay time (MPD) between the sender camera 101 and the receiver camera 102, and the time difference between the sender camera 101 and the receiver camera 102, i.e., the time correction amount of the receiver camera 102, can be calculated using the following equations (1) and (2).

[0052] Communication delay time (MPD) = {(T2-T1)+(T4-T3)} / 2 ···(1) Time correction amount = T2 - T1 - MPD ={(T2-T1)-(T4-T3)} / 2 ···(2)

[0053] The control unit 220 of the receiver camera 102 adjusts the amount of time advance of the receiver camera 102's clock function 212 so that the time correction amount calculated above becomes zero, since this is the offset amount of the receiver camera 102 relative to the sender camera 101. This allows for time synchronization with the sender camera 101.

[0054] Figure 5 is a flowchart showing the flow of the receiver camera 102 sending a message to increase the frequency of the time synchronization sequence. In this embodiment, since the communication delay time (MPD) is used to determine the frequency of the time synchronization sequence, the flow is the same as the time synchronization sequence shown in Figure 4 up to a certain point.

[0055] The synchronized shooting system 100 is an example of a time synchronization system. The sender camera 101 is an example of a communication device that is the source of synchronization. The receiver camera 102 is an example of a communication device that is the destination of synchronization. The processing method of the synchronized shooting system 100 will be described below.

[0056] Step S510 indicates the starting point of the flowchart and shows the state in which the receiver camera 102 is activated as one of the terminals constituting the synchronized imaging system 100 shown in Figure 1.

[0057] In step S520, the control unit 220 of the receiver camera 102 performs the initial setup flow shown in Figure 3. The control unit 220 of the receiver camera 102 performs the process of establishing a communication connection with other cameras. Here, the control unit 220 of the receiver camera 102 is set to be the synchronization target in the time synchronization sequence.

[0058] In step S530, the control unit 220 of the receiver camera 102 determines, via the communication unit 210, whether or not it has received the Sync packet and Follow Up packet shown in steps S410 and S411 of Figure 4. If the control unit 220 of the receiver camera 102 has received the Sync packet and Follow Up packet from the sender camera 101, it obtains the transmission time T1 and reception time T2 of the Sync packet and proceeds to step S540. If it has not received the Sync packet and Follow Up packet, it returns to step S530. The Follow Up packet includes the transmission time T1 of the Sync packet.

[0059] In step S540, the control unit 220 of the receiver camera 102 receives the Sync packet and Follow Up packet via the communication unit 210, and then sends the Delay Request packet shown in step S412 of Figure 4 to the sender camera 101. At this time, the control unit 220 of the receiver camera 102 records the time T3 of transmission of the Delay Request packet.

[0060] In step S550, the control unit 220 of the receiver camera 102 sends a Delay Request packet via the communication unit 210 and then determines whether or not it has received the Delay Response packet shown in S413 of Figure 4. If the control unit 220 of the receiver camera 102 has received a Delay Response packet from the sender camera 101, it obtains the time T4 of the Delay Request packet's reception and proceeds to step S560. If it has not received a Delay Response packet, it returns to step S550. The Delay Response packet includes the time T4 of the Delay Request packet's reception.

[0061] In step S560, the control unit 220 of the receiver camera 102 calculates the communication delay time (MPD) of the receiver camera 102 based on the results of the time synchronization sequence execution so far. The control unit 220 calculates the communication delay time (MPD) using equation (1) and the times T1 to T4 obtained in the processing of steps S520 to S550.

[0062] In step S570, the control unit 220 of the receiver camera 102 determines whether the communication delay time (MPD) calculated in step S560 is longer than a preset threshold. If the communication delay time (MPD) is longer than the threshold, the control unit 220 proceeds to step S571; otherwise, it proceeds to step S580.

[0063] Patent Document 1 describes a method that performs a time synchronization sequence defined by PTP multiple times, calculates the minimum communication delay time from among them, and then performs time correction based on the minimum communication delay time after performing the sequence a predetermined number of times.

[0064] Here, we will describe an example of threshold calculation. The control unit 220 of the receiver camera 102 stores the communication delay time (MPD) calculated for each execution of the time synchronization sequence in the temporary storage unit 230. The control unit 220 uses the smallest communication delay time (MPD) obtained in the past as the reference value, and adds or multiplies it by a predetermined value to set the threshold value. Furthermore, while the number of samples of communication delay time (MPD) obtained in the past is small, the control unit 220 uses the value set as the initial value as the threshold value.

[0065] In step S571, the control unit 220 of the receiver camera 102 sends a message to the sender camera 101 via the communication unit 210. If the communication delay time (MPD) calculated in step S560 is greater than or equal to a threshold, the control unit 220 of the receiver camera 102 sends a message (synchronization request message) to the sender camera 101, which is the synchronization source, requesting it to increase the frequency of sending Sync packets and Follow Up packets.

[0066] The synchronization request message is a message used to shorten the transmission interval between Sync packets and Follow Up packets.

[0067] The synchronization request message may be transmitted using a communication method other than the one used for PTP (Wi-Fi in this embodiment), such as Bluetooth. Furthermore, it may be transmitted on a different frequency and channel than those used for PTP, such as 2.4GHz and 5GHz in Wi-Fi.

[0068] Synchronization request messages may be sent using a different protocol than Sync packets and Follow Up packets. Furthermore, synchronization request messages may be sent using a different communication method than Sync packets and Follow Up packets.

[0069] Upon receiving a synchronization request message, the sender camera 101 shortens the transmission interval for Sync packets and Follow Up packets, and the receiver camera 102 performs the time synchronization sequence shown in Figure 4 more frequently. This allows for quick synchronization even when the time synchronization sequence is executed a predetermined number of times and the best result is extracted and used.

[0070] In step S580, the control unit 220 of the receiver camera 102 determines whether or not there has been an external stop command. If the control unit 220 has received an instruction to stop synchronization, either by the photographer or through a communication path from another camera, it proceeds to step S590; otherwise, it returns to step S530.

[0071] Step S590 indicates the end of the flowchart.

[0072] According to the above flow, in the time synchronization sequence, the receiver camera 102, which is the synchronization target, sends a synchronization request message to the synchronization source when the communication delay time (MPD) exceeds a threshold. Note that if a different time synchronization protocol such as NTP is used for time synchronization, each sequence should be interpreted accordingly.

[0073] (Second embodiment) As a second embodiment of the present invention, the behavior of the sender camera 101 in the first embodiment will be described. In the second embodiment, the sender camera 101, which is the synchronization source, has elapsed time in the temporary storage unit 230. The elapsed time is the difference between the time at a certain point in time in the clock function 212 and the current time, and becomes 0 when reset. The sender camera 101 also has a transmission interval for Sync packets and Follow Up packets, and transmits Sync packets and Follow Up packets at this interval. The transmission interval for Sync packets and Follow Up packets is predetermined and is set in the initial settings shown in Figure 3. There are also two types of transmission intervals for Sync packets and Follow Up packets: the default transmission interval for Sync packets and Follow Up packets, and a shorter transmission interval for Sync packets and Follow Up packets.

[0074] Figure 6 is a flowchart showing how the sender camera 101 synchronizes time with the receiver camera 102 in the synchronized shooting system 100 shown in Figure 1. The control unit 220 performs various processes by executing a program stored in the recording unit 260 or the temporary storage unit 230.

[0075] Step S610 indicates the starting point of the flowchart and shows that the sender camera 101 is activated as a terminal constituting the synchronized shooting system 100 shown in Figure 1.

[0076] In step S620, the control unit 220 of the sender camera 101 performs the initial setup flow shown in Figure 3. The control unit 220 of the sender camera 101 performs the process of establishing a communication connection with the receiver camera 102. Here, the control unit 220 of the sender camera 101 is set to become the synchronization source in the time synchronization sequence.

[0077] In step S630, the control unit 220 of the sender camera 101 performs a process to count the elapsed time. The control unit 220 takes the difference between the current time of the clock function 212 and the time when the elapsed time was last reset, and stores it as the elapsed time in the temporary storage unit 230.

[0078] In step S640, the control unit 220 of the sender camera 101 determines whether the elapsed time counted in step S630 matches the transmission interval of the Sync packet and Follow Up packet. If the elapsed time matches the transmission interval of the Sync packet and Follow Up packet, the control unit 220 proceeds to step S650; otherwise, it proceeds to step S630.

[0079] In step S650, the control unit 220 of the sender camera 101 performs a process to reset the elapsed time counted in step S630. The control unit 220 stores the current time of the clock function 212 in the temporary storage unit 230 as the time of the previous elapsed time reset.

[0080] In step S660, the control unit 220 of the sender camera 101 performs the process of sending Sync packets and Follow Up packets to the receiver camera 102. The details of this process are described in steps S661 to S669. The control unit 220 of the sender camera 101 sends Sync packets and Follow Up packets via the communication unit 210 and sets the transmission interval for the next Sync packets and Follow Up packets. If a short transmission interval for Sync packets and Follow Up packets is set here, the time from steps S630 to S650 will be shortened.

[0081] In step S670, the control unit 220 of the sender camera 101 determines whether or not there has been an external stop command. If the control unit 220 has received an instruction to stop synchronization, either by the photographer or through a communication path from another camera, it proceeds to step S680; otherwise, it returns to step S630.

[0082] Step S680 indicates the end of the flowchart.

[0083] Step S661 indicates the starting point for the transmission process of the Sync packet and Follow Up packet shown in step S660.

[0084] In step S662, the control unit 220 of the sender camera 101 sends a Sync packet to the receiver camera 102 via the communication unit 210. As a result, the control unit 220 of the receiver camera 102 obtains the time T1 of the transmission of the Sync packet.

[0085] In step S663, the control unit 220 of the sender camera 101 sends a Follow Up packet to the receiver camera 102 via the communication unit 210. As a result, the receiver camera 102 obtains the time T2 of receipt of the Follow Up packet.

[0086] In step S664, the control unit 220 of the sender camera 101 checks via the communication unit 210 whether it has received a synchronization request message from the receiver camera 102.

[0087] In step S665, the control unit 220 of the sender camera 101 determines whether to increase the transmission frequency of Sync packets and Follow Up packets sent to the receiver camera 102. If the control unit 220 receives a synchronization request message from the receiver camera 102, it determines to increase the transmission frequency of Sync packets and Follow Up packets. The control unit 220 of the sender camera 101 may also be configured to increase the transmission frequency of Sync packets and Follow Up packets several times after receiving the synchronization request message. In that case, the control unit 220 also counts how many times it has been determined to increase the transmission frequency of Sync packets and Follow Up packets after receiving the synchronization request message.

[0088] In step S666, the control unit 220 of the sender camera 101 determines whether or not it was determined in step S665 that the transmission frequency of Sync packets and Follow Up packets has increased. If the control unit 220 determines that the transmission frequency of Sync packets and Follow Up packets has increased, it proceeds to step S668; otherwise, it proceeds to step S667.

[0089] In step S667, the control unit 220 of the sender camera 101 changes the transmission frequency of the Sync packets and Follow Up packets to be sent. The control unit 220 of the sender camera 101 sets the default transmission interval for the Sync packets and Follow Up packets. If the system is configured to increase the transmission frequency of Sync packets and Follow Up packets several times after a synchronization request message is received, the count of whether the transmission frequency of Sync packets and Follow Up packets has been determined to have increased is reset here.

[0090] In step S668, the control unit 220 of the sender camera 101 changes the transmission frequency of the Sync packets and Follow Up packets to be transmitted. The control unit 220 of the sender camera 101 sets a short transmission interval for the Sync packets and Follow Up packets. This shortens the elapsed time until it is determined in step S640 that it is time to transmit the Sync packets and Follow Up packets. The transmission interval in step S668 is shorter than the transmission interval in step S667.

[0091] Step S669 indicates the completion of the transmission process for the Sync packet and Follow Up packet shown in step S660.

[0092] As described above, if the control unit 220 of the sender camera 101 does not receive a synchronization request message, it sends Sync packets and Follow Up packets at the first transmission interval in step S667. If the control unit 220 of the sender camera 101 does receive a synchronization request message, it sends Sync packets and Follow Up packets at the second transmission interval in step S668, which is shorter than the first transmission interval.

[0093] Furthermore, if the control unit 220 of the sender camera 101 receives a synchronization request message, it may transmit Sync packets and Follow Up packets a predetermined number of times at the second transmission interval in step S668, and then transmit Sync packets and Follow Up packets at the first transmission interval in step S667.

[0094] Furthermore, the control unit 220 of the receiver camera 102 may send a second message to the sender camera 101 to set the transmission interval for Sync packets and Follow Up packets to the default setting if the communication delay time (MPD) is not longer than a threshold. When the control unit 220 of the sender camera 101 receives the second message, it sends Sync packets and Follow Up packets at the first transmission interval of step S667.

[0095] As described above, when the sender camera 101 receives a synchronization request message from the receiver camera 102, it selects a short interval for sending Sync packets and Follow Up packets, increasing the execution frequency of the time synchronization sequence shown in Figure 4. This allows the synchronization to be completed quickly even in the synchronized imaging system 100, which performs the time synchronization sequence a predetermined number of times, by shortening the time required for each execution.

[0096] According to this embodiment, as the communication delay time increases, the frequency of the time synchronization sequence increases. By increasing the number of time synchronization sequences performed per unit time, a predetermined number of message exchanges can be completed quickly, preventing the time difference between the source and destination from widening.

[0097] (Other embodiments) This disclosure can also be implemented by supplying a program that implements one or more of the functions of the embodiments described above to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be implemented by a circuit (e.g., an ASIC) that implements one or more functions.

[0098] The above describes embodiments of the present invention. The present invention is not limited to the embodiments described above and can be modified without departing from the spirit of the invention.

[0099] This embodiment includes the following configuration. (Item 1) The first communication device that was the source of the synchronization, It has a second communication device that is synchronized with it, The second communication device is A first communication means for receiving time synchronization packets from the first communication device, A calculation means for calculating the communication delay time using the time of transmission of the time-synchronized packet and the time of reception of the time-synchronized packet, The device includes an adjustment means for adjusting the time of the clock function of the second communication device using a time correction amount based on the aforementioned communication delay time, A time synchronization system characterized in that the first communication means transmits a first message to the first communication device to shorten the transmission interval of the time synchronization packets when the communication delay time is longer than a threshold. (Item 2) The time synchronization system according to item 1, characterized in that the first message is transmitted using a protocol different from the time synchronization packet. (Item 3) The time synchronization system according to item 1 or 2, characterized in that the first message is transmitted using a communication method different from that of the time synchronization packet. (Item 4) The time synchronization system according to any one of items 1 to 3, characterized in that the first communication device has a second communication means that transmits the time synchronization packet at a first transmission interval if it does not receive the first message, and transmits the time synchronization packet at a second transmission interval shorter than the first transmission interval if it does receive the first message. (Item 5) The time synchronization system according to item 4, characterized in that when the second communication means receives the first message, it transmits the time synchronization packet a predetermined number of times at the second transmission interval, and then transmits the time synchronization packet at the first transmission interval. (Item 6) The time synchronization system according to item 4, characterized in that the first communication means sends a second message to the first communication device to set the transmission interval of the time synchronization packets to the default when the communication delay time is not longer than a threshold. (Item 7) The time synchronization system according to item 6, characterized in that when the second communication means receives the second message, it transmits the time synchronization packet at the first transmission interval. (Item 8) The time synchronization system according to any one of items 1 to 7, characterized in that the time synchronization packet is a PTP packet. (Item 9) The first communication means receives a first time synchronization packet from the first communication device and transmits a second time synchronization packet to the first communication device. The time synchronization system according to any one of items 1 to 8, characterized in that the calculation means calculates the communication delay time using the time of transmission of the first time synchronization packet, the time of reception of the first time synchronization packet, the time of transmission of the second time synchronization packet, and the time of reception of the second time synchronization packet. (Item 10) The first time synchronization packet is a Sync packet, The time synchronization system according to item 9, characterized in that the second time synchronization packet is a Delay Request packet. (Item 11) The time synchronization system according to item 10, characterized in that the first communication means receives a Follow Up packet containing the time of transmission of the Sync packet from the first communication device, and receives a Delay Response packet containing the time of transmission of the Delay Request packet from the first communication device. (Item 12) The time synchronization system according to any one of items 1 to 11, characterized in that the first communication device and the second communication device are controlled to perform synchronized shooting based on the time of the clock function of the first communication device and the time of the clock function of the second communication device, respectively. (Item 13) A communication device, A first communication means for receiving time synchronization packets from other communication devices, A calculation means for calculating the communication delay time using the time of transmission of the time-synchronized packet and the time of reception of the time-synchronized packet, The device includes an adjustment means for adjusting the time of the clock function of the communication device using a time correction amount based on the aforementioned communication delay time, The first communication means is characterized in that, when the communication delay time is longer than a threshold, it transmits a first message to the other communication device to shorten the transmission interval of the time synchronization packets. (Item 14) A communication device characterized by having communication means that, if a first message for shortening the transmission interval of time synchronization packets is not received, transmits the time synchronization packets at a first transmission interval, and if the first message is received, transmits the time synchronization packets at a second transmission interval shorter than the first transmission interval. (Item 15) The communication device according to item 14, characterized in that when the communication means receives the first message, it transmits the time synchronization packet a predetermined number of times at the second transmission interval, and then transmits the time synchronization packet at the first transmission interval. (Item 16) The communication device according to item 14, characterized in that when the second communication means receives a second message for setting the transmission interval of the time synchronization packet to the default, it transmits the time synchronization packet at the first transmission interval. (Item 17) The first communication device that was the source of the synchronization, A processing method for a time synchronization system having a second communication device as a synchronization target, The second communication device receives a time synchronization packet from the first communication device in a first communication step, The second communication device performs a calculation step of calculating the communication delay time using the time of transmission of the time synchronization packet and the time of reception of the time synchronization packet, The second communication device performs an adjustment step in which it adjusts the time of the clock function of the second communication device using a time correction amount based on the communication delay time, If the second communication device has a communication delay time longer than a threshold, it performs a second communication step of sending a first message to the first communication device to shorten the transmission interval of the time synchronization packets. A method for processing a time synchronization system, characterized by having the following features. (Item 18) A method for processing communication devices, A first communication step of receiving a time synchronization packet from another communication device, A calculation step of calculating the communication delay time using the time of transmission of the time synchronization packet and the time of reception of the time synchronization packet, An adjustment step to adjust the time of the clock function of the communication device using a time correction amount based on the aforementioned communication delay time, If the aforementioned communication delay time is longer than a threshold, a second communication step is to send a first message to the other communication device to shorten the transmission interval of the time synchronization packets. A method for processing a communication device, characterized by having the following features. (Item 19) A communication device processing method characterized by having a communication step of transmitting the time synchronization packets at a first transmission interval if a first message for shortening the transmission interval of time synchronization packets is not received, and transmitting the time synchronization packets at a second transmission interval shorter than the first transmission interval if the first message is received. (Item 20) A program to cause a computer to function as a communication device as described in any one of items 13-16. [Explanation of Symbols]

[0100] 100 Synchronized Shooting System 101 Sender Camera 102 Receiver Camera 210 Communications Department 220 Control Unit 230 Temporary storage 240 Synchronization signal generation unit 250 Imaging Control Unit 260 Records Section 270 Photography Department 280 Shutter button

Claims

1. The first communication device that was the source of the synchronization, It has a second communication device that is synchronized with it, The second communication device is A first communication means for receiving time synchronization packets from the first communication device, A calculation means for calculating the communication delay time using the time of transmission of the time-synchronized packet and the time of reception of the time-synchronized packet, The device includes an adjustment means for adjusting the time of the clock function of the second communication device using a time correction amount based on the aforementioned communication delay time, A time synchronization system characterized in that, when the communication delay time is longer than a threshold, the first communication means transmits a first message to the first communication device to shorten the transmission interval of the time synchronization packets.

2. The time synchronization system according to claim 1, characterized in that the first message is transmitted using a protocol different from the time synchronization packet.

3. The time synchronization system according to claim 1, characterized in that the first message is transmitted using a communication method different from that of the time synchronization packet.

4. The time synchronization system according to claim 1, characterized in that the first communication device has a second communication means that transmits the time synchronization packet at a first transmission interval if it does not receive the first message, and transmits the time synchronization packet at a second transmission interval shorter than the first transmission interval if it receives the first message.

5. The time synchronization system according to claim 4, characterized in that when the second communication means receives the first message, it transmits the time synchronization packet a predetermined number of times at the second transmission interval, and then transmits the time synchronization packet at the first transmission interval.

6. The time synchronization system according to claim 4, characterized in that the first communication means sends a second message to the first communication device to set the transmission interval of the time synchronization packets to the default when the communication delay time is not longer than a threshold.

7. The time synchronization system according to claim 6, characterized in that when the second communication means receives the second message, it transmits the time synchronization packet at the first transmission interval.

8. The time synchronization system according to claim 1, characterized in that the time synchronization packet is a PTP packet.

9. The first communication means receives a first time synchronization packet from the first communication device and transmits a second time synchronization packet to the first communication device. The time synchronization system according to claim 1, characterized in that the calculation means calculates the communication delay time using the time of transmission of the first time synchronization packet, the time of reception of the first time synchronization packet, the time of transmission of the second time synchronization packet, and the time of reception of the second time synchronization packet.

10. The first time synchronization packet is a Sync packet, The time synchronization system according to claim 9, characterized in that the second time synchronization packet is a Delay Request packet.

11. The time synchronization system according to claim 10, characterized in that the first communication means receives a Follow Up packet containing the time of transmission of the Sync packet from the first communication device and receives a Delay Response packet containing the time of transmission of the Delay Request packet from the first communication device.

12. The time synchronization system according to claim 1, characterized in that the first communication device and the second communication device are controlled to perform synchronized shooting based on the time of the clock function of the first communication device and the time of the clock function of the second communication device, respectively.

13. A communication device, A first communication means for receiving time synchronization packets from other communication devices, A calculation means for calculating the communication delay time using the time of transmission of the time-synchronized packet and the time of reception of the time-synchronized packet, The device includes an adjustment means for adjusting the time of the clock function of the communication device using a time correction amount based on the aforementioned communication delay time, The first communication means is characterized in that, when the communication delay time is longer than a threshold, it transmits a first message to the other communication device to shorten the transmission interval of the time synchronization packets.

14. A communication device characterized by having communication means that, if a first message for shortening the transmission interval of time synchronization packets is not received, transmits the time synchronization packets at a first transmission interval, and if the first message is received, transmits the time synchronization packets at a second transmission interval shorter than the first transmission interval.

15. The communication device according to claim 14, characterized in that when the communication means receives the first message, it transmits the time synchronization packet a predetermined number of times at the second transmission interval, and then transmits the time synchronization packet at the first transmission interval.

16. The communication device according to claim 14, characterized in that when the second communication means receives a second message for setting the transmission interval of the time synchronization packet to the default, it transmits the time synchronization packet at the first transmission interval.

17. The first communication device that was the source of the synchronization, A processing method for a time synchronization system having a second communication device as a synchronization target, The second communication device receives a time synchronization packet from the first communication device in a first communication step, The second communication device performs a calculation step of calculating the communication delay time using the time of transmission of the time synchronization packet and the time of reception of the time synchronization packet, The second communication device performs an adjustment step in which it adjusts the time of the clock function of the second communication device using a time correction amount based on the communication delay time, If the second communication device has a communication delay time longer than a threshold, it performs a second communication step of sending a first message to the first communication device to shorten the transmission interval of the time synchronization packets. A method for processing a time synchronization system, characterized by having the following features.

18. A method for processing communication devices, A first communication step of receiving a time synchronization packet from another communication device, A calculation step of calculating the communication delay time using the time of transmission of the time synchronization packet and the time of reception of the time synchronization packet, An adjustment step to adjust the time of the clock function of the communication device using a time correction amount based on the aforementioned communication delay time, If the aforementioned communication delay time is longer than a threshold, a second communication step is to send a first message to the other communication device to shorten the transmission interval of the time synchronization packets. A method for processing a communication device, characterized by having the following features.

19. A communication device processing method characterized by having a communication step of transmitting the time synchronization packets at a first transmission interval if a first message for shortening the transmission interval of time synchronization packets is not received, and transmitting the time synchronization packets at a second transmission interval shorter than the first transmission interval if the first message is received.

20. A program for causing a computer to function as a communication device according to any one of claims 13 to 16.

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