Time distribution apparatus

Abstract

To reduce a difference between values of a plurality of time counters used for a plurality of synchronous processes.SOLUTION: The time distribution apparatus includes a first transmission unit configured to transmit, to a first external apparatus, time information based on a value of a first time counter for first synchronization processing, a second transmission unit configured to transmit, to a second external apparatus, time information based on a value of a second time counter for second synchronization processing, and a correction unit configured to perform correction for making the value of the first time counter and the value of the second time counter coincide with each other.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present disclosure relates to a time distribution device, a synchronized photography system, a processing method for a time distribution device, and a program. [Background technology]

[0002] In recent years, there has been an increase in cases where electronic devices such as digital cameras, printers, mobile phones, and smartphones are equipped with wireless communication functions and are connected to wireless networks for use.

[0003] Patent Document 1 discloses a technique in which a digital camera as a slave performs time synchronization with a digital camera as a master using wireless communication packets, thereby realizing synchronized shutters among a plurality of digital cameras.

[0004] Furthermore, Patent Document 2 discloses a technique for reducing the time difference between the time distribution devices in a redundant synchronous network using a plurality of time distribution devices. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-66898 [Patent Document 2] Japanese Patent Application Publication No. 2020-77929 Summary of the Invention [Problem to be solved by the invention]

[0006] When performing synchronized shooting with multiple cameras, if the communication methods (wired / wireless) and time synchronization mechanisms of each camera are different, the time distribution device must support multiple time distribution methods. Furthermore, to prevent deterioration of synchronization accuracy of the entire system, it is necessary to properly handle the distributed time information between each of the multiple distribution methods.

[0007] An object of the present disclosure is to make it possible to reduce the difference between the values ​​of multiple time counters used for multiple synchronization processes. [Means for solving the problem]

[0008] The time distribution device has a first transmitting means for transmitting time information based on the value of a first time counter for a first synchronization process to a first external device, a second transmitting means for transmitting time information based on the value of a second time counter for a second synchronization process to a second external device, and a correction means for correcting the value of the first time counter and the value of the second time counter to match each other. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to reduce the difference between the values ​​of multiple time counters used for multiple synchronization processes. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a synchronized shooting system for multiple cameras. [Figure 2] FIG. 2 is a block diagram showing an example of the configuration of a time distribution device. [Figure 3] FIG. 2 is a block diagram showing an example of the configuration of a timer control unit. [Figure 4] FIG. 2 is a diagram illustrating a group of software executed by a control unit. [Figure 5] 10 is a flowchart showing a processing method of the time distribution device. [Figure 6] FIG. 1 is a diagram illustrating time synchronization using PTP. [Figure 7] 10 is a flowchart of common synchronization executed by the control unit. [Figure 8] FIG. 1 is a diagram illustrating time synchronization using FTM. [Figure 9] 10 is a flowchart of wireless synchronization executed by a wireless control packet processing unit. [Figure 10] 10 is a timing chart of the time adjustment process. [Figure 11] FIG. 1 is a diagram illustrating an example of the configuration of a synchronized shooting system for multiple cameras. [Figure 12] FIG. 2 is a block diagram showing an example of the configuration of a time distribution device. [Figure 13] 10 is a timing chart of the time adjustment process. DETAILED DESCRIPTION OF THE INVENTION

[0011] (First embodiment) The time distribution device according to the present embodiment will be described below with reference to the drawings. Note that the technical scope of the present disclosure is determined by the claims and is not limited to the individual embodiments described below.

[0012] 1 is a diagram showing an example of the configuration of a synchronized photography system 100 according to the first embodiment. The synchronized photography system 100 includes a time distribution device 101, a plurality of cameras 102 to 105, and wireless networks 110 and 120.

[0013] The time distribution device 101 operates as a parent device of wireless networks 110 and 120, and establishes the wireless networks 110 and 120 with cameras 102 to 105. Here, an example will be described in which a wireless LAN conforming to the IEEE802.11 series is used for wireless communication. Wireless communication also includes short-range wireless communication, such as Near Field Communication (registered trademark) (hereinafter referred to as NFC) and Bluetooth. A configuration may be used in which some or all of the wireless communication methods are used together, or in which they are implemented as separate functional blocks, or in which only some of the methods are implemented.

[0014] The time distribution device 101 also has a function of distributing time to the cameras 102 to 105, and transmits control information for synchronous shooting. The time distribution device 101 also has an imaging function like the cameras 102 to 105, and may participate in synchronous shooting.

[0015] The time distribution device 101 and cameras 102 to 105 can perform synchronous shooting at the same time by communicating control information for synchronous shooting. By the time distribution by the time distribution device 101, the time of the cameras 102 to 105 is corrected to the same time as the time distribution device 101. This makes it possible for the time distribution device 101 and cameras 102 to 105 to perform synchronous shooting.

[0016] The cameras 102 and 103 implement a time synchronization method (hereinafter referred to as the wireless synchronization method) with the time distribution device 101 using a wireless-specific protocol, and perform time synchronization processing with the time distribution device 101. The cameras 102 and 103 capture images based on the time synchronization processing of the wireless synchronization method.

[0017] The cameras 104 and 105 implement a time synchronization method that does not rely on wireless / communication (hereinafter referred to as the common synchronization method) and perform time synchronization processing with the time distribution device 101. The cameras 104 and 105 capture images based on the time synchronization processing of the common synchronization method.

[0018] The details of both methods will be explained later. This concludes the explanation of Figure 1.

[0019] Fig. 2 is a block diagram showing an example configuration of the time distribution device 101 in Fig. 1. The time distribution device 101 has a control unit 201, an input unit 202, a display unit 203, a storage unit 204, an imaging unit 205, a system bus 206, a wireless communication unit 251, and a time control unit 301B. The wireless communication unit 251 has an antenna 207, a packet processing unit 252, and a time control unit 301A. The packet processing unit 252 has a user packet processing unit 253 and a wireless control packet processing unit 254.

[0020] The control unit 201 executes control programs stored in the storage unit 204 to control the entire time distribution device 101. Each control program will be described later. The control unit 201 is configured by, for example, a CPU (Central Processing Unit).

[0021] The input unit 202 is a device for a user to input various information, and has an operation function for operating the time distribution device 101.

[0022] The display unit 203 displays various information and has a function of outputting visually perceptible information such as an LCD or LED.

[0023] The storage unit 204 stores the control program executed by the control unit 201, the imaging data generated by the imaging unit 205, and communication packets used for sending and receiving wireless / wired communications with other devices.

[0024] The imaging unit 205 is a block that generates an image by performing imaging processing. The imaging unit 205 has a mode in which it operates at a timing instructed via a system bus 206, and a mode in which primitive timing control can be performed by an imaging timing signal 209. The imaging unit 205 performs imaging processing based on the imaging timing signal 209.

[0025] The wireless communication unit 251 is a wireless communication unit for performing wireless LAN communication. The wireless communication unit 251 includes a packet processing unit 252 that performs processing for transmitting and receiving packets, a time control unit 301A that manages time information accompanying packet processing, and an antenna 207 that is used for wireless communication.

[0026] The packet processing unit 252 includes a user packet processing unit 253 that performs transmission and reception processing mainly on IP packets required by users / applications. IP packets are packets that are processed as data frames in a wireless LAN. The packets handled here are all packets except for PTP packets used in synchronization processing, which will be described later. For example, image packets that require transmission and reception of image information during synchronized shooting and various control packets that are required when performing synchronized shooting are processed as user packets.

[0027] When a packet is transmitted or received, a transmission / reception interrupt signal 208 is asserted. The transmission / reception interrupt signal 208 is input to the control unit 201 and a time control unit 301B (described later). When a user packet is received, the packet is stored in the storage unit 204.

[0028] The packet processing unit 252 includes a wireless control packet processing unit 254. The wireless control packet processing unit 254 processes management frames and control frames that are required when wireless communication is performed between wireless LAN terminals. The wireless control packet processing unit 254 also processes time distribution to the cameras 102-103 using a wireless synchronization method.

[0029] The radio control packet processing unit 254 receives time information 255 from the time control unit 301A. The time information 255 is used to control various processing timings required for time distribution using a radio synchronization method, store the processing timings, and insert time into packets. The time information 255 is generated and supplied by the time control unit 301A.

[0030] In the following explanation, the reference numeral A indicates time control unit 301A or a component of time control unit 301A. Similarly, the reference numeral B indicates time control unit 301B (described later) or a component of time control unit 301B. Hereinafter, time control units 301A and 301B will be collectively referred to as time control unit 301.

[0031] Fig. 3 is a diagram showing an example of the configuration of time control unit 301. Time control unit 301A supplies time information 255 to radio control packet processing unit 254. Time control unit 301 is applicable to time control unit 301A in Fig. 2 and time control unit 301B, which will be described later. Time control unit 301 will be described in detail using Fig. 3.

[0032] The time control unit 301 has a trigger input port 302, a bus interface 303, a time information output port 304, and a timing signal output port 305. The time control unit 301 also has a register unit 306, a time stamp processing unit 307, a counter correction unit 308, a time counter unit 309, and a timing signal generation unit 310.

[0033] The timestamp processing unit 307 receives time information 315, which is output from the time counter unit 309 and whose value is updated sequentially, and a trigger 311, which is input via the trigger input port 302. The timestamp processing unit 307 has a function of storing the time information 315 at the timing when the trigger 311 is detected, and outputting it as a timestamp value 312.

[0034] The time counter unit 309 is a counter that indicates time, and counts a value in response to an operation pulse 316. The time counter unit 309 has a function of performing correction using correction information 314 input from a counter correction unit 308.

[0035] The correction information 314 includes two pieces of information: correction method information and the amount of correction used in that method. There are preferably three types of correction methods. The first is a method in which the counter value is directly overwritten (direct value correction method). The second is a method in which an addition / subtraction value is received from the counter value and an addition / subtraction correction is performed by that value (offset correction method). The third is a method in which a value is added to the counter when the operating pulse 316 is generated, i.e., a correction is performed on the amount of time advance per unit time (frequency correction method).

[0036] The timing signal generation unit 310 has a function of outputting a timing signal 317 having a fixed cycle. The timing signal generation unit 310 can generate a timing signal with a fixed cycle by changing the signal between 1 and 0 each time the value of time information 315 advances by a predetermined amount. The time to start generation and the frequency are set by the setting information 313.

[0037] The register unit 306 is a register accessed by the control unit 201, and is configured so that the control unit 201 can set setting information 313 for the counter correction unit 308 and the timing signal generation unit 310. The register unit 306 is also configured so that time information 315 and a timestamp value 312 can be checked.

[0038] The interface between the time control unit 301 and the outside world comprises a trigger input port 302, a time information output port 304, a timing signal output port 305, and a bus interface 303. This concludes the description of the time control unit 301.

[0039] Returning to the explanation of the time control unit 301A in Fig. 2, the time control unit 301A is configured to receive an imaging timing signal 209 output from a time control unit 301B (described later) at a trigger input port 302A and generate a timestamp. Note that the timing signal output port 305A is not used in this embodiment. This concludes the explanation of the time control unit 301A.

[0040] Next, the time control unit 301B will be described. The time control unit 301B manages the time information used in the common synchronization method. The time control unit 301B is also responsible for generating an image capture timing signal 209 for the image capture unit 205. A timing signal generation unit 310B of the time control unit 301B generates the image capture timing signal 209 based on time information 315 from the time counter unit 309B. The frequency of the image capture timing signal 209 may be, for example, the frame rate, or if the image capture unit 205 generates timing separately, it may be generated as a 1 Hz PPS (Pulse Per Second) signal for synchronization. Note that in this embodiment, the time information output port 304B is not used. This concludes the description of the time control unit 301B.

[0041] The imaging timing signal 209 is also input to the control unit 201, so that the control unit 201 can detect the imaging timing. The control unit 201 is configured to generate a timestamp using the generation of the transmission / reception interrupt signal 208 as a trigger. This timestamp is used in a common synchronization system, as will be described in detail later.

[0042] The system bus 206 is a bus used for accessing each functional block from the control unit 201 and for transferring various data (packet data, imaging data, etc.) This concludes the explanation of FIG.

[0043] FIG. 4 is a diagram for explaining the software executed by the control unit 201. Application software 401 is software for various applications run by the time distribution device 101. Imaging control software 405 is software that controls the imaging unit 205. Wireless communication control software 402 is software that controls the wireless communication unit 251. Time processing unit control software 406 is software that controls the time control units 301A and 301B. Communication protocol processing software 403 is software that processes various communication protocols. Among the communication protocols, PTP processing software 404 that processes PTP (Precision Time Protocol) used in the common synchronization method is also included in the communication protocol processing software 403. This concludes the explanation of FIG. 4.

[0044] Next, we will explain the operation of the time distribution device 101. First, the overall processing will be explained using the flowchart in FIG.

[0045] 5 is a flowchart showing the processing method of the time distribution device 101. In step S500, the control unit 201 uses the wireless communication unit 251 to build a wireless LAN network and wirelessly connects the cameras 102 to 105. Thereafter, the control unit 201 continues to execute the processing of multiple steps S501 to S504 in parallel.

[0046] In step S501, the control unit 201 uses the value of the time counter unit 309B of the time control unit 301B to perform common synchronization processing, which is processing for time synchronization with the cameras 104 to 105. Details of this processing will be described later.

[0047] In step S502, the control unit 201 uses the value of the time counter unit 309A of the time control unit 301A to perform wireless synchronization processing for time synchronization with the cameras 102 and 103. Details of this processing will be described later.

[0048] In step S503, the control unit 201 performs a time adjustment process to eliminate the time difference between the common synchronization method and the wireless synchronization method. This process will be described in detail later.

[0049] The details of the processing of the above three steps S501 to S503 will be described later. By the processing of these three steps S501 to S503, the control unit 201 continues to establish / maintain a synchronized state between all the cameras 102 to 105 / time distribution device 101, and furthermore, the control unit 201 separately performs processing for synchronized shooting (processing from S504 onwards).

[0050] In step S504, the control unit 201 checks the number of cameras 102 to 105 for synchronized shooting. If the control unit 201 can determine the number of cameras in each synchronization method, it may use that information, or if it cannot determine the number of cameras, it may be provided with a separate application for that purpose.

[0051] In step S505, the control unit 201 determines whether or not a predetermined number of cameras 102 to 105 have been connected. If the predetermined number of cameras 102 to 105 have been connected (Yes in S505), the process proceeds to step S506. If the predetermined number of cameras 102 to 105 have not been connected (No in S505), the process returns to step S504.

[0052] In step S506, the control unit 201 checks the synchronization accuracy of the cameras 102 to 105. The control unit 201 may implement an application for receiving feedback on the synchronization accuracy from each of the cameras 102 to 105, or may use a synchronization method if it can be checked within the synchronization method.

[0053] In step S507, the control unit 201 determines whether or not the required synchronization accuracy has been achieved for all of the cameras 102 to 105. If the required synchronization accuracy has been achieved for all of the cameras 102 to 105 (Yes in S507), the process proceeds to step S508. If the required synchronization accuracy has not been achieved for all of the cameras 102 to 105 (No in S507), the process returns to step S507.

[0054] In step S508, the control unit 201 determines the time to start generating the imaging timing signal 209.

[0055] In step S509, the control unit 201 notifies each of the cameras 102 to 105 of the determined image capture timing signal generation start time via the wireless communication unit 251. This notification is also performed via the wireless networks 110 and 120, so the start time must be determined taking into consideration this network delay and the processing latency of each of the cameras 102 to 105.

[0056] In step S510, the control unit 201 causes the time control unit 301B to start generating the imaging timing signal 209. In this process, the control unit 201 sets the setting information 313 to be passed to the timing signal generation unit 310 of the time control unit 301B in the register unit 306. As a result, the cameras 102 to 105 and the time distribution device 101 start generating the imaging timing signal 209 from the same time, and become ready for the timing signal for synchronous shooting.

[0057] In step S511, the control unit 201 determines the image capture timing start time and notifies all the cameras 102 to 105 of this.

[0058] In step S512, if the time distribution device 101 has the image capturing unit 205, the control unit 201 causes the image capturing unit 205 to start capturing an image.

[0059] In step S513, the control unit 201 determines whether or not the termination condition is satisfied. If the termination condition is satisfied (Yes in S513), the process ends. If the termination condition is not satisfied (No in S513), the process proceeds to step S514.

[0060] In step S514, the control unit 201 continues to perform synchronous imaging, and returns to step S513. This concludes the description of FIG.

[0061] Next, a common synchronization method will be described. The common synchronization method is an example of a synchronization method using the PTPv2 protocol (hereinafter referred to as PTP) defined in IEEE1588-2008.

[0062] 6 is a diagram showing PTP processing. In PTP, synchronization processing is performed by periodically transmitting and receiving four packets between terminals: a Sync packet (S601), a FollowUp packet (S602), a DelayRequest packet (S603), and a DelayResponse packet (S604).

[0063] In step S601, the time distribution device 101 transmits a Sync packet at time T1. The camera 104 receives the Sync packet at time T2.

[0064] In step S602, the time distribution device 101 transmits a FollowUp packet including the time T1. The camera 104 receives the FollowUp packet including the time T1.

[0065] In step S603, the camera 104 transmits a DelayRequest packet at time T3. The time distribution device 101 receives the DelayRequest packet at time T4.

[0066] In step S604, the time distribution device 101 transmits a DelayResponse packet including time T4. The camera 104 receives the DelayResponse packet including time T4.

[0067] Time T1 is the time acquired by the clock of the time distribution device 101 when the Sync packet was transmitted in step S601.

[0068] Time T2 is the time obtained using the clock of the camera 104 when the Sync packet was received in step S601.

[0069] Time T3 is the time when the DelayRequest packet was transmitted in step S603, obtained using the clock of the camera 104.

[0070] Time T4 is the time obtained by using the clock of the time distribution device 101 when the DelayRequest packet was received in step S603.

[0071] Of the packets transmitted from the time distribution device 101, the FollowUp packet in step S602 is given information of time T1, and the DelayRequest packet in step S604 is given information of time T4, and these packets are transmitted to the camera 104.

[0072] This allows the camera 104 to obtain information on times T1, T2, T3, and T4. From the information on times T1, T2, T3, and T4, the transmission delay time, which is the network delay time, and the offset, which is the time difference between the time distribution device 101 and the camera 104, can be calculated using the following formulas.

[0073] Transmission delay time = ((T2-T1)+(T4-T3)) / 2 Offset = ((T2-T1)-(T4-T3)) / 2

[0074] For example, the camera 104 can correct the clock of the camera 104 by (T1 + transmission delay time) or (T2 - offset). This allows the clock of the camera 104 to be synchronized with the clock of the time distribution device 101. This concludes the explanation of PTP.

[0075] FIG. 7 is a flowchart showing the details of the synchronization process of the time distribution device 101 in the common synchronization method in step S501 of FIG.

[0076] In step S701, the control unit 201 determines whether it is time to transmit a Sync packet. If it is time to transmit a Sync packet (Yes in S701), the process proceeds to step S702. If it is not time to transmit a Sync packet (No in S701), the process proceeds to step S704.

[0077] In step S702, the control unit 201 functions as a transmitting unit, and transmits a Sync packet to the camera 104 or 105 via the wireless communication unit 251 via the wireless network 120. The control unit 201 creates a Sync packet in the storage unit 204 using the PTP processing software 404, and issues a transmission instruction to the wireless communication unit 251, thereby realizing the processing of step S702. The cameras 104 and 105 are examples of external devices.

[0078] In step S703, the wireless communication unit 251 asserts the transmission / reception interrupt signal 208 upon completing transmission of the Sync packet. At this timing, the timestamp processing unit 307B of the time control unit 301B generates a timestamp value 312 based on the time information 315 of the time counter unit 309B. The control unit 201 stores this timestamp value 312 in the storage unit 204 as time T1.

[0079] In step S704, the control unit 201 determines whether it is time to send a FollowUp packet. If it is time to send a FollowUp packet (Yes in S704), the process proceeds to step S705. If it is not time to send a FollowUp packet (No in S704), the process proceeds to step S707.

[0080] In step S705, the control unit 201 creates a FollowUp packet including the previous time T1 using the PTP processing software 404.

[0081] In step S706, the control unit 201 transmits a FollowUp packet including time T1 to the camera 104 or 105 via the wireless network 120. Time T1 is an example of time information based on the value of the time counter unit 309B of the time control unit 301B for synchronization processing in the common synchronization method. Time T1 is time information based on the value of the time counter unit 309B when the Sync packet is transmitted to the camera 104 or 105.

[0082] In step S707, the control unit 201 determines whether or not a DelayRequest packet has been received from the camera 103 or 104 via the wireless network 120 via the wireless communication unit 251. If a DelayRequest packet has been received (Yes in S707), the process proceeds to step S708. If a DelayRequest packet has not been received (No in S707), the process proceeds to step S710.

[0083] In step S708, the wireless communication unit 251 asserts the transmission / reception interrupt signal 208 upon completing reception of the DelayRequest packet. At this timing, the timestamp processing unit 307B of the time control unit 301B generates a timestamp value 312 based on the time information 315 of the time counter unit 309B. The control unit 201 stores this timestamp value 312 in the storage unit 204 as time T4.

[0084] In step S709, the control unit 201 creates a DelayResponse packet including time T4. Then, the control unit 201 transmits the DelayResponse packet including time T4 to camera 103 or camera 104 (the one that transmitted the DelayRequest packet) via the wireless network 120 using the wireless communication unit 251. Time T4 is an example of time information based on the value of the time counter unit 309B of the time control unit 301B for synchronization processing in the common synchronization method. Time T4 is time information based on the value of the time counter unit 309B when the DelayRequest packet is received from camera 104 or 105.

[0085] In step S710, the control unit 201 determines whether or not the termination condition is satisfied. If the termination condition is not satisfied (No in S710), the process returns to step S701. If the termination condition is satisfied (Yes in S710), the process of the flowchart in FIG. 7 ends.

[0086] This concludes the description of the common synchronization method. Here, a timestamp is generated each time the transmit / receive interrupt signal 208 is asserted, so processing such as deleting unnecessary timestamps as appropriate is required. In this case, if the wireless communication unit 251 has a mechanism for changing the interrupt method for each packet type, such processing can be omitted by using this mechanism, but since this is not the main part of this embodiment, detailed description will be omitted. This concludes the description of Figure 7.

[0087] Next, the wireless synchronization method will be described with reference to Fig. 8. The wireless synchronization method is an example of a synchronization method that uses FTM (Fine Time Measurement) defined in IEEE802.11mc.

[0088] In step S801, the camera 102 transmits an FTM request packet. The time distribution device 101 receives the FTM request packet.

[0089] In step S802, the time distribution device 101 transmits an ACK packet. The camera 102 receives the ACK packet.

[0090] In step S803, the time distribution device 101 transmits an FTM1 packet at time t1, and the camera 102 receives the FTM1 packet at time t2.

[0091] In step S804, the camera 102 transmits an FTM ACK1 packet at time t3. The time distribution device 101 receives the FTM ACK1 packet at time t4.

[0092] In step S805, the time distribution device 101 transmits an FTM2 packet including times t1 and t4. The camera 102 receives the FTM2 packet including times t1 and t4.

[0093] In step S806, the camera 102 transmits an FTM ACK2 packet. The time distribution device 101 receives the FTM ACK2 packet.

[0094] The above FTM transmission and reception are repeated multiple times. When transmitting an FTM packet, the time distribution device 101 stores the transmission timing as time t1, and stores the reception timing when receiving an FTM ACK packet as time t4. When transmitting an FTM packet, the time distribution device 101 assigns the times t1 and t4 from the previous attempt to the FTM packet and transmits it (FTM2, S805).

[0095] Meanwhile, the camera 102 stores the reception timing of the FTM1 packet in step S803 as time t2 and the transmission timing of the FTM ACK1 packet in step S804 as time t3, thereby enabling the camera 102 to acquire times t1, t2, t3, and t4.

[0096] The camera 102 can correct the time of the camera 102 using times t1 to t4 in the same way as in the common synchronization method described above. This allows the clock of the camera 104 to be synchronized with the clock of the time distribution device 101.

[0097] The camera 104 can improve accuracy by performing acquisition / calculation multiple times from time t1 to time t4. This concludes the explanation of FIG.

[0098] Fig. 9 is a flowchart showing details of the synchronization process of the wireless synchronization method in step S502 in Fig. 5. It should be noted that all processes are executed by the wireless control packet processing unit 254 in the wireless communication unit 251.

[0099] In step S901, the wireless control packet processing unit 254 determines whether or not an FTM request packet has been received from the camera 102 or 103 via the wireless network 110. The cameras 102 and 103 are examples of external devices. If an FTM request packet has been received (Yes in S901), the process proceeds to step S902. If an FTM request packet has not been received (No in S901), the process proceeds to step S905.

[0100] In step S902, the wireless control packet processing unit 254 functions as a transmitting unit and transmits an ACK packet to the camera 102 or 103 via the wireless network 110.

[0101] In step S903, the wireless control packet processing unit 254 transmits an FTM packet to the camera 102 or 103 via the wireless network 110.

[0102] In step S904, the radio control packet processing unit 254 saves the time information 255 of the time counter unit 309A of the time control unit 301A at the time of transmitting the FTM packet as time t1.

[0103] In step S905, the wireless control packet processing unit 254 determines whether or not an FTM ACK packet has been received from the camera 102 or 103 via the wireless network 110. If an FTM ACK packet has been received from the camera 102 or 103 (Yes in S905), the process proceeds to step S906. If an FTM ACK packet has not been received from the camera 102 or 103 (No in S905), the process proceeds to step S908.

[0104] In step S906, the radio control packet processing unit 254 stores the time information 255 of the time counter unit 309A of the time control unit 301A at the timing of receiving the FTM ACK packet as time t4.

[0105] In step S907, the wireless control packet processor 254 transmits an FTM packet including times t1 and t4 to the camera 102 or 103 via the wireless network 110.

[0106] Times t1 and t4 are examples of time information based on the value of time counter unit 309A of time control unit 301A for synchronization processing in the wireless synchronization method. Time t1 is time information based on the value of time counter unit 309A when an FTM packet is transmitted to camera 102 or 103. Time t4 is time information based on the value of time counter unit 309A when an FTM ACK packet is received from camera 102 or 103.

[0107] In step S908, the wireless control packet processing unit 254 determines whether or not the termination condition is satisfied. If the termination condition is not satisfied (No in S908), the process returns to step S901. If the termination condition is satisfied (Yes in S908), the process of the flowchart in FIG. 9 ends.

[0108] The above process is continued until the end condition is met (Yes in S908). This concludes the explanation of FIG.

[0109] Fig. 10 is a timing chart showing details of the time adjustment process in step S503 in Fig. 5. Fig. 10 is a timing chart in which the horizontal axis represents the passage of time for the operation of each processing block.

[0110] In step S1001, the control unit 201 starts the time adjustment process by transmitting a request to generate the imaging timing signal 209 to the time control unit 301B.

[0111] In step S1002, the register unit 306B of the time control unit 301B receives a request to generate the imaging timing signal 209.

[0112] In step S1003, the time counter unit 309B increments the counter value as time passes.

[0113] In step S1004, the timing signal generation unit 310B starts timing signal generation processing. An example will be described in which a request is set for the timing signal generation unit 310B to generate the imaging timing signal 209 every time the counter value of the time counter unit 309B becomes a multiple of 20. In this case, the timing signal generation unit 310B generates the imaging timing signal 209 every time the value of the time counter unit 309B becomes a predetermined multiple.

[0114] In step S1006, the timing signal generation unit 310B asserts the imaging timing signal 209 when the counter value of the time counter unit 309B reaches 180 (the timing at which the imaging timing signal 209 is generated). The timing signal generation unit 310B transmits the imaging timing signal 209 to the control unit 201 and the time control unit 301A.

[0115] In step S1007, the time counter unit 309A increments the counter value as time passes.

[0116] In step S1008, when the time stamp processing unit 307A of the time control unit 301A receives the imaging timing signal 209, it acquires the time information (value 182) 315 of the time counter unit 309A at that time.

[0117] In step S1009, timestamp processing unit 307A transmits time information (value 182) 315 to register unit 306A.

[0118] In step S1010, register unit 306A holds time information (value 182) 315 as a timestamp value.

[0119] In steps S1011 to S1013, when the control unit 201 detects that the imaging timing signal 209 is asserted, it acquires a timestamp value from the register unit 306A.

[0120] The control unit 201 may acquire a timestamp value in step S1014. In step S1014, the control unit 201 knows that the time counter unit 309B indicates a value of 180 at the time when the imaging timing signal 209 is asserted. Therefore, the control unit 201 may use a value obtained by calculating this value as the timestamp value. Furthermore, if the time control unit 301B can hold a timestamp value at the assertion timing of the imaging timing signal 209, the control unit 201 may acquire this value as the timestamp value.

[0121] In step S1015, the control unit 201 obtains the value 180 of time counter unit 309B at the timing of step S1006 and the value 182 of time counter unit 309A, and compares the two values. In this example, it is found that the value 180 of time counter unit 309B is 2 behind the value 182 of time counter unit 309A.

[0122] In step S1016, the control unit 201 calculates the amount of correction based on the result. In this example, the control unit 201 uses offset correction for ease of understanding. That is, the control unit 201 uses the previous comparison result of 2 as the amount of correction.

[0123] In steps S1017 and S1018, the control unit 201 sets the correction amount in the counter correction unit 308B.

[0124] In steps S1019 and S1020, counter correction unit 308B adds 3 to the value 192 of time counter unit 309B, which was originally incremented by 1 at that increment, by adding the correction amount 2 to the original increment value 1. Counter correction unit 308B then performs correction so as to set the value 195 resulting from the addition in time counter unit 309B.

[0125] Counter correction unit 308B performs correction so that the value of time counter unit 309A and the value of time counter unit 309B match each other. Counter correction unit 308B performs correction every time the value of time counter unit 309B becomes a predetermined multiple (for example, a multiple of 20).

[0126] Thereafter, in steps S1021 to S1024, the time distribution device 101 repeatedly executes the same processing as above, triggered by the assertion of the imaging timing signal 209. This allows the time to be steadily synchronized even if the values ​​of the time counter unit 309B and the time counter unit 309A become misaligned due to, for example, a slight difference in the amount of advance. This concludes the explanation of FIG. 10.

[0127] (Second embodiment) In the first embodiment, an example has been shown in which both synchronization methods are used under wireless communication. Also, a method of synchronizing the time between the two synchronization methods using a periodic image capture timing signal 209 has been shown.

[0128] In the second embodiment, an example is shown in which a network in which both wireless and wired connections are used, and an example is shown in which a signal different from the periodic image capture timing signal 209 is used as a time synchronization method.

[0129] 11 is a diagram showing an example of the configuration of a synchronized photography system 1100 according to the second embodiment. The synchronized photography system 1100 includes a time distribution device 1101, multiple cameras 102, 103, 1104, and 1105, a wireless network 110, and a wired network 1120. The wired network 1120 includes a hub 1106. The cameras 102 and 103 and the wireless network 110 are the same as those in FIG. 1.

[0130] The time distribution device 1101 can simultaneously use the wireless network 110 and the wired network 1120, and performs synchronization processing with four cameras 102, 103, 1104, and 1105. The cameras 1104 and 1105 are compatible with wired LANs, and are connected to the time distribution device 1101 via a PTP-compatible hub 1106.

[0131] The time distribution device 101 communicates with cameras 102 and 103 via a wireless network 110 for synchronization processing using the wireless synchronization method. The time distribution device 101 also communicates with cameras 1104 and 1105 via a wired network 1120 for synchronization processing using the common synchronization method. This concludes the explanation of FIG. 11.

[0132] Figure 12 is a diagram showing an example of the configuration of the time distribution device 1101 in Figure 11. Only the differences between the time distribution device 1101 in Figure 12 and the time distribution device 101 in Figure 2 will be explained. The time distribution device 1101 in Figure 12 is obtained by adding a wired communication unit 1201 to the time distribution device 101 in Figure 2.

[0133] The wired communication unit 1201 performs communication compatible with a wired LAN. The wired communication unit 1201 is connected to external devices such as the hub 1106 via a cable 1202. The wired communication unit 1201 notifies the control unit 201 of a wired interrupt signal 1203 when a packet is transmitted or received.

[0134] Furthermore, both time control units 301A and 301B are configured to acquire a timestamp value at the assertion timing of wired interrupt signal 1203. The control unit 201 is able to acquire the timestamp values ​​generated by time control units 301A and 301B via system bus 206. This completes the explanation of FIG. 12. Here, wired control software is added to the software executed by the control unit 201. There are no differences from the other software.

[0135] 13 is a timing chart showing the time adjustment process in step S503 of FIG. 5, which is executed by the time distribution device 1101. Like FIG. 10, FIG. 13 is a timing chart in which the horizontal axis represents the passage of time. The following explanation will focus on the differences between FIG. 13 and FIG. 10. The time adjustment process is started by a wired interrupt signal 1203 from the wired communication unit 1201.

[0136] In step S 1301 , the wired communication unit 1201 receives a packet from the camera 1104 or 1105 .

[0137] In step S1302, the wired communication unit 1201 notifies the control unit 201, the timestamp processing unit 307A, and the timestamp processing unit 307B of the wired interrupt signal 1203.

[0138] Although the wired communication unit 1201 is triggered by the reception of a packet, it may also use a wired interrupt signal 1203 for transmitting a packet. Also, the notification in step S1302 may be separated from the wired interrupt signal 1203, and may be configured to be notified only at the timing of transmitting or receiving a specific packet such as PTP.

[0139] In step S1303, register unit 306A holds, as a timestamp value, the value 182 of time counter unit 309A at the timing when timestamp processing unit 307A receives the notification.

[0140] In step S1304, register unit 306B holds, as a timestamp value, the value 180 of time counter unit 309B at the timing when timestamp processing unit 307B receives the notification.

[0141] In step S1305, the control unit 201 obtains the timestamp value from the register unit 306A.

[0142] In step S1306, the control unit 201 obtains the timestamp value from the register unit 306B.

[0143] Steps S1307 to S1310 are the same as the processes in steps S1015 to S1019 in FIG. 10. In step S1307, the control unit 201 compares the two timestamp values. In step S1308, the control unit 201 calculates the amount of correction. In the first embodiment, offset correction is used, but if the amount of correction is too small, frequency correction may be preferable. Also, if synchronization is lost due to some trigger and an event occurs in which the amount of correction is large, absolute value correction may be preferable. Also, a method may be used in which statistical information such as the transition of past correction results is used to select the correction method and calculate the amount of correction.

[0144] In step S1309, the control unit 201 sets the correction amount in the counter correction unit 308B via the register unit 306B.

[0145] In step S1310, counter correction unit 308B performs actual correction processing. Counter correction unit 308B performs correction based on the reception timing or transmission timing of the packet via wired network 1120 in step S1301. Note that counter correction unit 308B may also perform correction based on the reception timing or transmission timing of a specific packet. This concludes the explanation of FIG. 13.

[0146] (Third embodiment) To perform time-synchronized photography, the camera must have a synchronization function. If the time distribution devices 101 and 1101 of the first and second embodiments are used, processing on the camera side is also possible. However, the synchronization function requires software that operates as a synchronization destination, not as a synchronization source (distribution side).

[0147] In all the embodiments, an example has been described in which the time on the time control unit 301B side is corrected, but a method of correcting the time on the time control unit 301A side may also be used. Which one is to be the synchronization source time may be determined based on the functional difference, if any, between the time synchronization control units, or may be determined by processing such as selecting which of the two synchronization networks was established first as the synchronization source. It may also be determined based on the precision of the oscillators that generate the operating pulses 316 used in each.

[0148] The time control unit 301A and the time control unit 301B may be arranged in two in the same IC, or one each in separate ICs. For example, in Fig. 2, the wireless communication unit 251 may be configured as a single IC. In the first and second embodiments, an example has been described in which the imaging timing signal 209 is generated using a function provided in the time control unit 301B, but it is also possible to provide an equivalent function in the time control unit 301A and use that function.

[0149] In the first and second embodiments, an example was described in which the time information output port 304B is not used. For example, in the second embodiment, if the wired communication unit 1201 is configured to be able to acquire a timestamp value, the time information for that purpose may be input from the time information output port 304B.

[0150] Although the method of using the FTM of IEEE802.11mc as the wireless synchronization method has been described, other control / management frames may also be used as long as they are configured to handle the timestamp value of a specific packet.

[0151] In the first and second embodiments, two synchronization methods (common synchronization method and wireless synchronization method) have been described, but other methods may be used. For example, if the wired communication unit 1201 shown in Fig. 12 can use a synchronization method whose specifications are expected for wired communication, such as SYNCE, two modes, the wired synchronization method and the wireless synchronization method, may be supported. Of the multiple synchronization modes, only one synchronization mode may be operated depending on the system configuration.

[0152] As described above, according to the first to third embodiments, the synchronized shooting system 100 or 1100 can support a plurality of time distribution methods with one time distribution device 101 or 1101. Furthermore, the time distribution device 101 or 1101 can reduce the difference in time information between the time distribution methods, and can precisely time synchronize many cameras (communication devices) 102 to 105, 1104 to 1105.

[0153] (Other embodiments) The present disclosure can also be realized by a process in which a program that realizes one or more functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in the computer of the system or device read and execute the program. The present disclosure can also be realized by a circuit (e.g., ASIC) that realizes one or more functions.

[0154] It should be noted that the above-described embodiments merely illustrate specific examples of implementing the present disclosure, and the technical scope of the present disclosure should not be construed as being limited by these embodiments. In other words, the present disclosure can be implemented in various forms without departing from its technical concept or main features.

[0155] The disclosure of this embodiment includes the following configuration, method, and program. (Configuration 1) a first transmitting means for transmitting time information based on a value of a first time counter for a first synchronization process to a first external device; a second transmitting means for transmitting time information based on a value of a second time counter for a second synchronization process to a second external device; a correction means for correcting the value of the first time counter and the value of the second time counter so that they coincide with each other; A time distribution device comprising: (Configuration 2) the first transmitting means transmits time information based on the value of the first time counter via a first wireless network; 2. The time distribution device according to configuration 1, wherein the second transmission means transmits time information based on the value of the second time counter via a second wireless network. (Configuration 3) the first transmitting means transmits time information based on the value of the first time counter via a wireless network; 2. The time distribution device according to configuration 1, wherein the second transmission means transmits time information based on the value of the second time counter via a wired network. (Configuration 4) the first transmitting means transmits time information based on the value of the first time counter using a first synchronization method; The time distribution device according to any one of configurations 1 to 3, characterized in that the second transmission means transmits time information based on the value of the second time counter using a second synchronization method different from the first synchronization method. (Configuration 5) 5. The time distribution device according to configuration 4, wherein the second synchronization method is a synchronization method using PTP. (Configuration 6) the first synchronization method is a synchronization method using FTM, 5. The time distribution device according to configuration 4, wherein the second synchronization method is a synchronization method using PTP. (Configuration 7) 7. The time distribution device according to any one of configurations 1 to 6, further comprising imaging means for performing imaging processing based on an imaging timing signal based on the value of the second time counter. (Configuration 8) the first transmitting means transmits, to the first external device, time information based on a value of the first time counter when a first packet is transmitted to the first external device, and time information based on a value of the first time counter when a second packet is received from the first external device; The time distribution device according to any one of configurations 1 to 7, characterized in that the second transmitting means transmits to the second external device time information based on the value of the second time counter when a third packet is transmitted to the second external device, and time information based on the value of the second time counter when a fourth packet is received from the second external device. (Configuration 9) the first transmitting means transmits, to the first external device, time information based on a value of the first time counter when an FTM packet is transmitted to the first external device, and time information based on a value of the first time counter when an FTM ACK packet is received from the first external device; The time distribution device according to configuration 6, wherein the second transmitting means transmits to the second external device time information based on the value of the second time counter when a Sync packet is transmitted to the second external device, and time information based on the value of the second time counter when a DelayRequest packet is received from the second external device. (Configuration 10) 8. The time distribution device according to claim 7, wherein the correction means performs the correction based on the timing of generation of the imaging timing signal. (Configuration 11) 11. The time distribution device according to configuration 10, further comprising timing signal generating means for generating the imaging timing signal each time the value of the second time counter reaches a predetermined multiple. (Configuration 12) 12. The time distribution device according to any one of configurations 1 to 11, wherein the correction means performs the correction every time the value of the second time counter reaches a predetermined multiple. (Configuration 13) 10. The time distribution device according to any one of configurations 1 to 9, wherein the correction means performs the correction based on a timing of receiving or transmitting a packet via a wired network. (Configuration 14) 14. The time distribution device according to configuration 13, wherein the correction means performs the correction based on the reception timing or transmission timing of a specific packet. (Configuration 15) The time distribution device according to any one of configurations 1 to 14, the first external device; the second external device; the first external device performs imaging based on the first synchronization processing; The second external device performs imaging based on the second synchronization process. (Method 1) a first transmission step of transmitting time information based on a value of a first time counter for a first synchronization process to a first external device; a second transmission step of transmitting time information based on a value of a second time counter for a second synchronization process to a second external device; a correction step of correcting the value of the first time counter and the value of the second time counter so that they coincide with each other; A processing method for a time distribution device, comprising: (Program 1) A program for causing a computer to function as the time distribution device according to any one of the first to fourteenth aspects. [Explanation of symbols]

[0156] 201 control unit, 202 input unit, 203 display unit, 204 storage unit, 205 imaging unit, 206 system bus, 207 antenna, 251 wireless communication unit, 252 packet processing unit, 253 user packet processing unit, 254 wireless control packet processing unit, 301A, 301B time control unit

Claims

1. a first transmitting means for transmitting time information based on a value of a first time counter for a first synchronization process to a first external device; a second transmitting means for transmitting time information based on a value of a second time counter for a second synchronization process to a second external device; a correction means for correcting the value of the first time counter and the value of the second time counter so that they coincide with each other; A time distribution device comprising:

2. the first transmitting means transmits time information based on the value of the first time counter via a first wireless network; 2. The time distribution device according to claim 1, wherein the second transmission means transmits the time information based on the value of the second time counter via a second wireless network.

3. the first transmitting means transmits time information based on the value of the first time counter via a wireless network; 2. The time distribution device according to claim 1, wherein the second transmission means transmits the time information based on the value of the second time counter via a wired network.

4. the first transmitting means transmits time information based on the value of the first time counter by a first synchronization method; The time distribution device according to claim 1, characterized in that the second transmission means transmits time information based on the value of the second time counter using a second synchronization method different from the first synchronization method.

5. 5. The time distribution device according to claim 4, wherein the second synchronization method is a synchronization method using PTP.

6. the first synchronization method is a synchronization method using FTM, 5. The time distribution device according to claim 4, wherein the second synchronization method is a synchronization method using PTP.

7. 2. The time distribution device according to claim 1, further comprising an imaging unit that performs imaging processing based on an imaging timing signal that is based on the value of the second time counter.

8. the first transmitting means transmits, to the first external device, time information based on a value of the first time counter when a first packet is transmitted to the first external device, and time information based on a value of the first time counter when a second packet is received from the first external device; The time distribution device according to claim 1, characterized in that the second transmitting means transmits to the second external device time information based on the value of the second time counter when a third packet is transmitted to the second external device, and time information based on the value of the second time counter when a fourth packet is received from the second external device.

9. the first transmitting means transmits to the first external device time information based on a value of the first time counter when an FTM packet is transmitted to the first external device, and time information based on a value of the first time counter when an FTM ACK packet is received from the first external device; The time distribution device according to claim 6, characterized in that the second transmitting means transmits to the second external device time information based on the value of the second time counter when a Sync packet is transmitted to the second external device, and time information based on the value of the second time counter when a Delay Request packet is received from the second external device.

10. 8. The time distribution device according to claim 7, wherein the correction means performs the correction based on the timing of generation of the imaging timing signal.

11. 11. The time distribution device according to claim 10, further comprising a timing signal generating means for generating the image capture timing signal each time the value of the second time counter reaches a predetermined multiple.

12. 2. The time distribution device according to claim 1, wherein the correction means performs the correction each time the value of the second time counter reaches a predetermined multiple.

13. 2. The time distribution device according to claim 1, wherein the correction means performs the correction based on the timing of receiving or transmitting a packet via a wired network.

14. 14. The time distribution device according to claim 13, wherein the correction means performs the correction based on the reception timing or transmission timing of a specific packet.

15. A time distribution device according to any one of claims 1 to 14; the first external device; the second external device; the first external device performs imaging based on the first synchronization processing; The synchronized photographing system is characterized in that the second external device performs photographing based on the second synchronization processing.

16. a first transmission step of transmitting time information based on a value of a first time counter for a first synchronization process to a first external device; a second transmission step of transmitting time information based on a value of a second time counter for a second synchronization process to a second external device; a correcting step of correcting the value of the first time counter and the value of the second time counter so that they coincide with each other; A processing method for a time distribution device, comprising:

17. A program for causing a computer to function as the time distribution device according to any one of claims 1 to 14.

Images