JP2018063171A - Electronic apparatus, display system, time synchronization method, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic apparatus that easily brings a time error due to time synchronization into a predetermined range even in a network environment where a difference in delay time easily occurs between an outward path and a return path of communication.SOLUTION: An electronic apparatus comprises: a synchronization packet receiving part 502 that receives a time synchronization packet transmitted from a time management device; a time synchronization part 509 that synchronizes the time managed by the electronic apparatus with the time to be a reference for the management performed by the time management device on the basis of time information included in the time synchronization packet; a delay time calculation part 504 that calculates an outward and return delay time of the time synchronization packet on the basis of the time information included in the time synchronization packet; a minimum delay time storage part 505 that stores the minimum delay time being the minimum value of the outward and return delay time; a delay error calculation part 506 that calculates a delay error being the difference between the outward and return delay time and the minimum delay time; and a time synchronization determination part 507 that, when the delay error is larger than a predetermined threshold, stops synchronization of time performed by the time synchronization part.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an electronic device, a display system, a time synchronization method, and a program.

  A display system that displays a large screen by combining a plurality of display devices such as a projector and a display is known (see, for example, Patent Document 1).

  For example, in such a display system, a network protocol called NTP (Network Time Protocol) is known as a time synchronization method for displaying a predetermined image at the same timing among a plurality of display devices. In addition, in order to reduce the influence due to the propagation delay time of the synchronization packet in time synchronization, there is known a client device that performs time synchronization by removing packets whose propagation delay time of the synchronization packet greatly deviates from the average value (for example, , See Patent Document 2).

  For example, in a display system that displays a large screen by combining a plurality of display devices, there is a problem in that display timing is shifted between display devices if there is an error in time information of each display device.

  However, in the conventional time synchronization method, the accuracy of time synchronization decreases due to the influence of variations in the delay time between the forward path and the return path of communication with the time synchronization server for performing time synchronization. For this reason, for example, in a network environment where a difference in the delay time between the forward and backward communication is likely to occur, such as a wireless local area network (LAN), the time information may be updated to incorrect time information. It was difficult to keep within the range. Note that such a problem is not limited to display devices, and is common to various electronic devices that execute predetermined processing in synchronization with other devices.

  The embodiments of the present invention have been made in view of the above-described problems. Even in a network environment in which a difference is likely to occur in the delay time between the communication forward path and the return path, the time error due to time synchronization is within a predetermined range. It is an object of the present invention to provide an electronic device that can be easily accommodated in a package.

  In order to solve the above-described problem, an electronic device according to an embodiment of the present invention is an electronic device that synchronizes time with a time management device that manages a reference time, and the first device transmits the time to the time management device. Based on the synchronization packet receiving unit that receives the second time synchronization packet transmitted from the time management device according to the time synchronization packet, and the time information included in the second time synchronization packet, the time management device A time synchronization unit that synchronizes the time managed by the electronic device with the reference time to be managed, and transmission of the first time synchronization packet based on time information included in the second time synchronization packet; A delay time calculation unit for calculating a round trip delay time required for transmitting the second time synchronization packet; and a minimum delay time storage for storing a minimum delay time which is a minimum value of the round trip delay time. A delay error calculation unit that calculates a delay error that is a difference between the round trip delay time calculated by the delay time calculation unit and the minimum delay time stored in the minimum delay time storage unit; and the delay error calculation A time synchronization determination unit that stops time synchronization by the time synchronization unit when the delay error calculated by the unit is greater than a predetermined threshold.

  According to an embodiment of the present invention, there is provided an electronic device that makes it easy to keep a time error due to time synchronization within a predetermined range even in a network environment in which a difference is likely to occur between the communication forward and return delay times. can do.

It is a figure which shows an example of the system configuration | structure of the display system which concerns on one Embodiment. It is a figure which shows the example of the hardware constitutions of the projector which concerns on one Embodiment. It is a figure which shows an example of a function structure of the display system which concerns on one Embodiment. It is a figure which shows another example of a function structure of the display system which concerns on one Embodiment. It is a function block diagram of the time synchronous client part which concerns on one Embodiment. It is a figure for demonstrating the outline | summary of NTP which concerns on one Embodiment. It is a figure for demonstrating the minimum delay time and delay error which concern on one Embodiment. It is a flowchart which shows the example of the time synchronous process which concerns on 1st Embodiment. It is a flowchart which shows the example of the time synchronous process which concerns on 2nd Embodiment. It is a flowchart which shows the example of the time synchronous process which concerns on 3rd Embodiment. It is a sequence diagram which shows the example of the multi projection process which concerns on one Embodiment.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

<System configuration>
FIG. 1 is a diagram illustrating an example of a configuration of a display system according to an embodiment. A display system 100 illustrated in FIG. 1 includes, for example, a plurality of projectors 101-1 to 101-3 and an information terminal 102 that are communicably connected via a network 103 such as a wireless local area network (LAN) or a wired LAN. . In the following description, “projector 101” is used to indicate an arbitrary projector among a plurality of projectors. Further, the number of the plurality of projectors 101-1 to 101-3 is an example, and may be another number of two or more.

  The projector 101 is an example of a display device used in the display system 100 that displays a predetermined image using a plurality of display devices. The display device used in the display system 100 may be another display device such as a liquid crystal display, for example.

  The projector 101 is an example of an electronic device that executes predetermined processing (display processing, audio output processing, etc.) in synchronization with the time of another projector 101. The electronic device may be, for example, an audio output device that outputs sound by synchronizing time information with other devices, or an imaging device that performs shooting by synchronizing time information with other devices. good. Here, the following description will be made assuming that the electronic device is the projector 101.

  The projector 101 is an image projection apparatus that projects a projection image on the projection surface 104. As shown in FIG. 1, for example, the display system 100 is arranged so that a projection area (display area) 105-1 of the projector 101-1 and a projection area 105-2 of the projector 101-2 overlap. ing. Further, the projection area 105-2 of the projector 101-2 and the projection area 105-3 of the projector 101-3 are arranged so as to partially overlap each other. In addition, the display system 100 uses the three projection areas 105-1 to 105-3 to display one or more projection images (moving images or still images) 106 in a projection area wider than each projection area. (Multi-projection) can be performed.

  The projector 101 can acquire image data to be projected using an external storage device such as a USB (Universal Serial Bus) memory, the network 103, or the like.

  The information terminal 102 is an information processing apparatus such as a PC (Personal Computer) or a tablet terminal, for example, and communicates image data, control information, and the like via a plurality of projectors 101-1 to 101-3 and the network 103. It can be performed. The network 103 is an example of a communication unit between the plurality of projectors 101-1 to 101-3 and the information terminal 102. The communication means may be, for example, a wireless PAN (Personal Area Network) such as UWB (Ultra Wide Band) or a wired communication such as a cable. The information terminal 102 controls the above-described multi-projection using a plurality of projectors 101-1 to 101-3.

  In the above configuration, a plurality of projectors 101-1 to 101-3 project one image of each projection area 105-1 to 105-3 at the same timing according to control information from the information terminal 102. Projected image 106 is projected.

  Each projector 101 has a function of a time management server that manages a reference time, and for example, functions as a time management server (time management device) in accordance with an instruction from the information terminal 102. Each projector 101 has a function of a time synchronization client that communicates with a time management server and synchronizes time. For example, the projector 101 functions as a time synchronization client in accordance with an instruction from the information terminal 102.

  For example, in FIG. 1, the projector 101-1 functions as a time management server, and the projectors 101-2 and 101-3 are synchronized with the projector 101-1 as the time synchronization client. .

  Thereby, the plurality of projectors 101-1 to 101-3 project one or more contents (moving images, still images, etc.) on the projection plane 104 at the same timing according to the schedule instructed from the information terminal 102, for example. can do.

  Note that there are individual differences in the way the clocks of the projectors 101 have, and the same time cannot be maintained over time. Therefore, the projectors 101-2 and 101-3 that function as time synchronization clients periodically perform time synchronization processing on the projector 101-1 that functions as a time management server.

  At this time, for example, time synchronization can be performed using NTP (Network Time Protocol) which is a time synchronization protocol via a network. However, in the time synchronization processing using NTP, it is assumed that the delay time of the forward path and the backward path are the same using the round trip delay time of the time synchronization packet transmitted and received between the time management server and the time synchronization client. Calculate the time difference of the time synchronization client. Therefore, for example, in a wireless LAN, when there is a difference between the forward delay time and the backward delay time of the network 103, the time cannot be accurately synchronized with the time management server. The display timing of 101 may be shifted.

  Therefore, the projector (electronic device) 101 according to the present embodiment has a function of holding the minimum value of the round-trip delay time of the time synchronization packet as optimum network environment information. Further, the projector 101 functioning as a time synchronization client is configured such that the delay error, which is the difference between the round trip delay time required for the round trip of the time synchronization packet, and the minimum value of the round trip delay time is greater than a predetermined threshold. Cancel the synchronization process.

  Preferably, the predetermined threshold is determined based on an allowable error that is an error in time allowed by projector 101 (or display system 100). For example, the predetermined threshold value is set to a value that is twice or less than twice the allowable error.

  This is because, in NTP, time synchronization is performed on the assumption that the forward delay time and the return delay time of the time synchronization packet are the same, so the difference between the round trip delay time and the minimum round trip delay time is This is because half may occur as the maximum value of the time error in the time synchronization client. Note that a value twice the allowable error allowed by the projector 101 is an example of a threshold value for keeping the time information error within a predetermined range.

  With the above configuration, according to the present embodiment, an electronic device (projector 101) that makes it easy to keep a time error within a predetermined range even in a network environment in which a difference is likely to occur between the communication forward and return delay times. ) Can be provided.

  In the above description, the projector 101-1 has the function of the time management server. However, the function of the time management server is the information terminal 102 or other information processing apparatus on the network 103. May have.

<Hardware configuration>
(Hardware configuration of projector)
Here, a hardware configuration of the projector 101 as an example of the electronic apparatus according to the present embodiment will be described.

  FIG. 2 is a diagram illustrating a hardware configuration example of the projector according to the embodiment. The projector 101 has a general computer configuration. For example, a CPU (Central Processing Unit) 201, a memory 202, a storage unit 203, a network I / F (Interface) 204, an external connection I / F 205, an RTC ( Real Time Clock) 206, an image processing unit 207, an audio output unit 208, an image projection unit 209, an operation unit 210, and the like.

  The CPU 201 is an arithmetic device that implements each function of the projector 101 by reading a program and data from the memory 202, the storage unit 203, and the like and executing processing. The memory 202 is a storage device including, for example, a RAM (Random Access Memory) used as a work area of the CPU 201, a ROM (Read Only Memory) that stores a startup program of the projector 101, and the like.

  The storage unit 203 is a large-capacity storage unit that stores the program of the projector 101, image data, and the like, and includes, for example, an SSD (Solid State Drive), an HDD (Hard Disk Drive), or the like.

  A network I / F 204 is a communication interface such as a wireless LAN or a wired LAN for connecting the projector 101 to the network 103 and communicating with the information terminal 102, another projector 101, or the like.

  The external device I / F 405 is an interface for connecting an external device to the projector 101. The external device includes, for example, a recording medium such as a USB memory, a memory card, and an optical disk, another projector 101, and the like.

  The RTC 206 is a device that provides a clock function for measuring the current date and time.

  The image processing unit 207 performs various image processing such as decoding, scaling, and clipping on image data to be projected, for example, a GPU (Graphics Processing Unit) or an ASIC (Application Specific Integrated Circuit). Composed of etc.

  The audio output unit 208 includes an audio circuit that outputs audio included in image data (for example, moving image data), a speaker, and the like.

  The image projection unit 209 includes a light source, a display element, a projection lens, and the like for projecting an image on the projection plane 104. The operation unit 210 is an input device such as a key or a touch panel for receiving a user operation. The bus 211 is connected to each of the above components and transmits an address signal, a data signal, various control signals, and the like.

(Information terminal hardware configuration)
The information terminal 102 is a general-purpose information processing apparatus such as a PC, and has a general computer configuration. For example, the information terminal 102 includes a CPU, a memory, a storage unit, a network I / F, an external connection I / F, an RTC, and the like, similar to the projector 101 illustrated in FIG.

<Functional configuration>
(Functional configuration of display system)
FIG. 3 is a diagram illustrating an example of a functional configuration of the display system according to the embodiment. FIG. 3 shows an example of the functional configuration of the display system 100 shown in FIG. In FIG. 3, the display system 100 includes three projectors 101-1 to 101-3 and an information terminal 102. The number of projectors 101 shown in FIG. 3 is an example.

  When each projector 101 receives request information for instructing to function as a time management server from the information terminal 102 or the like, the projector 101 validates the time management server unit 302 and functions as a time management server.

  When each projector 101 receives request information for instructing time synchronization with the time management server from the information terminal 102 or the like, the projector 101 enables the time synchronization client unit 301 and functions as a time synchronization client.

  In the example of FIG. 3, the projector 101-1 functions as a time management server, and includes a time management server unit 302 and a display control unit 303.

  The time management server unit 302 is realized by, for example, a program executed by the CPU 201 in FIG. 2, and causes the projector 101 to function as a time management server (time management device) that manages a reference time. For example, the time management server unit 302 has a function of a general NTP server. When a time synchronization packet including a transmission time t0 is received from an electronic device (projectors 101-2 and 101-3), the reception time t1 And a time synchronization packet including a reply time t2. The transmission time t0, the reception time t1, and the reply time t2 will be described later.

  The display control unit 303 is realized by, for example, a program executed by the CPU 201 in FIG. 2, and controls the image processing unit 207, the image projection unit 209, and the like in accordance with a control signal from the information terminal 102, and displays an instructed image. Projection (display) is performed on the projection surface 104.

  In the example of FIG. 3, the projectors 101-2 and 101-3 function as a time synchronization client, and include a time synchronization client unit 301 and a display control unit 303.

  The time synchronization client unit 301 is realized by, for example, a program executed by the CPU 201 in FIG. 2 and causes the projectors 101-2 and 101-3 to function as a time synchronization client that synchronizes time with the time management server. For example, the time synchronization client unit 301 of the projector 101-2 transmits a time synchronization packet to the time management server unit 302, and uses the time information t0, t1, and t2 included in the returned time management packet to project the projector 101- 2 times are synchronized. A detailed functional configuration of the time synchronization client unit 301 will be described later with reference to FIG.

  The time synchronization client unit 301 of the projector 101-2 may communicate with the time management server unit 302 via the network 103, or communicate via the communication path 103a different from the network 103. It may be. Similarly, the time synchronization client unit 301 of the projector 101-3 may communicate with the time management server unit 302 via the network 103, or communicate via a communication path 103 b different from the network 103. It may be what performs.

  The communication paths 103a and 103b different from the network 103 include, for example, wired communication by cable connection, various short-range wireless communication, and the like. Here, the time synchronization client unit 301 performs the following description on the assumption that the time synchronization client unit 301 communicates with the time management server unit 302 via the network 103.

  The information terminal 102 has a display management unit 304. The display management unit 304 is realized by a program executed by the CPU of the information terminal 102 and the like, and is a multi-projection that displays one projection image 106 on the projection plane 104 using the three projectors 101-1 to 101-3. Management and control.

  At this time, the display management unit 304 sends request information for requesting one of the three projectors 101-1 to 101-3 (for example, the projector 101-1) to function as a time management server. Send. In addition, the display management unit 304 synchronizes the time with the time management server for the other two of the three projectors 101-1 to 101-3 (for example, the projectors 101-2 and 101-3). Request information for requesting is transmitted.

  FIG. 4 is a diagram illustrating another example of the functional configuration of the display system according to the embodiment. As illustrated in FIG. 4, the time management server unit 302 may be included in the information terminal 102. In this case, the information terminal 102 functions as a time management server, and the three projectors 101-1 to 101-3 function as time synchronization clients.

  Further, the display system 100 does not necessarily have the time management server unit 302. In this case, the three projectors 101-1 to 101-3 synchronize time with an external NTP server or the like connected via the network 103 as a time synchronization client.

(Functional configuration of the time synchronization client part)
FIG. 5 is a functional configuration diagram of a time synchronization client unit according to an embodiment. In FIG. 5, the time management server unit 302 functions as a general NTP server, and the time synchronization client unit 301 performs time synchronization with the time management server unit 302 using, for example, an NTP protocol. Will be explained.

  The time synchronization client unit 301 includes a synchronization packet transmission unit 501, a synchronization packet reception unit 502, a time synchronization information calculation unit 503, a delay time calculation unit 504, a minimum delay time storage unit 505, a delay error calculation unit 506, and a time synchronization determination unit 507. , An allowable error storage unit 508, a time synchronization unit 509, a time management unit 510, an initialization unit 511, and an operation mode management unit 512.

  The synchronization packet transmission unit 501 transmits a time synchronization packet (first time synchronization packet) for performing time synchronization to the time management server unit 302. The first time synchronization packet includes information on the transmission time t0 when the synchronization packet transmission unit 501 transmits the time synchronization packet.

  The synchronization packet receiving unit 502 receives a time synchronization packet (second time synchronization packet) transmitted from the time management server unit 302 according to the time synchronization packet transmitted by the synchronization packet transmission unit 501. In the second time synchronization packet transmitted from the time management server unit 302, the time management server unit 302 returns the reception time t1 at which the first time synchronization packet was received and the second time synchronization packet. Information on the reply time t2 is included. Further, the second time synchronization packet includes information of the transmission time t0 when the time synchronization client unit 301 transmits the first time synchronization packet.

  The synchronization packet receiving unit 502 includes information such as t0, t1, and t2 included in the received second time synchronization packet, and the time t3 when the synchronization packet receiving unit 502 received the second time synchronization packet. The calculation unit 503 and the delay time calculation unit 504 are notified.

  The time synchronization information calculation unit 503 uses the time information t0, t1, t2, and t3 received from the synchronization packet reception unit 502 to synchronize the time of the time synchronization client unit 301 with the time managed by the time management server unit 302. Time synchronization information for calculating the time is calculated. For example, the time synchronization information calculation unit 503 calculates the time difference between the reference time managed by the time management server unit 302 and the time managed by the time synchronization client unit 301.

  FIG. 6 is a diagram for explaining the outline of the NTP according to the embodiment. NTP is a protocol for a time synchronization client to synchronize time with a time management server connected via a network.

  At time t0 in FIG. 6, the synchronization packet transmission unit 501 of the time synchronization client unit 301 transmits the first time synchronization packet 601 including the transmission time t0 to the time management server unit 302.

  In FIG. 6, the time of the time synchronization client unit 301 when the first synchronization packet is transmitted is t0, and the time of the time management server unit 302 is t0 ′. The first time synchronization packet 601 includes t0 as the transmission time on the time synchronization client unit 301 side.

  At time t 1 on the time management server unit 302 side, the time management server unit 302 receives the first time synchronization packet 601.

  At time t2 on the time management server unit 302 side, the time management server unit 302 transmits a second time synchronization packet 602 including time information t0, t1, and t2 to the time synchronization client unit 301.

  At time t3 on the time synchronization client unit 301 side, the synchronization packet receiving unit 502 on the time synchronization client unit 301 side receives the second time synchronization packet 602.

At this time, the forward delay time required for transmission of the first time synchronization packet is d1, the return delay time required for transmission of the second time synchronization packet is d2, and the round trip delay time required for round trip of the time synchronization packet. If di is, then the round trip delay time di is expressed by the following equation (1).
di = d1 + d2 = (t3-t0)-(t2-t1) (1)
Assuming that there is no difference between the forward delay time d1 and the backward delay time d2, the time difference ci between the time t0 ′ on the time management server unit 302 side and the time t0 on the time synchronization client unit 301 side is: It is represented by the following formula (2).
ci = t0'-t0 = ((t1 + t2)-(t0 + t3)) / 2
= ((T1-t0) + (t2-t3)) / 2 (2)
For example, the time synchronization information calculation unit 503 calculates the time difference ci between the time t0 ′ on the time management server unit 302 side and the time t0 on the time synchronization client unit 301 side.

  Here, returning to FIG. 5, the description of the functional configuration of the time synchronization client unit 301 is continued.

  The delay time calculation unit 504 calculates the round-trip delay time di using the time information t0, t1, t2, and t3 received from the synchronous packet reception unit 502 and the above equation (1).

  The minimum delay time storage unit 505 stores the minimum delay time, which is the minimum value of the round trip delay time, in, for example, the storage unit 203 or the memory 202 in FIG.

  Preferably, the minimum delay time storage unit 505 calculates the round trip delay time di calculated when the round trip delay time di calculated by the delay time calculation unit 504 is shorter than the minimum delay time stored by the minimum delay time storage unit 505. Is stored as the minimum delay time.

  The delay error calculation unit 506 calculates a delay error that is a difference between the round trip delay time di calculated by the delay time calculation unit 504 and the minimum delay time stored in the minimum delay time storage unit 505.

  FIG. 7 is a diagram for explaining a minimum delay time and a delay error according to an embodiment. Assume that the minimum delay time storage unit 505 stores the minimum delay time 1 at time T1 in FIG.

  At time T2, the difference between the round trip delay time 711 calculated by the delay time calculation unit 504 and the minimum delay time (minimum delay time 1) stored in the minimum delay time storage unit 505 is defined as a delay error 721. At time T2, the minimum delay time storage unit 505 has the round trip delay time 711 calculated by the delay time calculation unit 504 longer than the minimum delay time (minimum delay time 1) stored in the minimum delay time storage unit 505. The calculated round trip time 711 is not stored as the minimum delay time. Further, the delay error calculation unit 506 calculates the difference between the round trip delay time 711 calculated by the delay time calculation unit 504 and the minimum delay time (minimum delay time 1) stored in the minimum delay time storage unit 505 as a delay error. 721 is calculated.

  At time T3, the round-trip delay time 712 calculated by the delay time calculation unit 504 is shorter than the minimum delay time (minimum delay time 1) stored in the minimum delay time storage unit 505. In this case, the minimum delay time storage unit 505 stores the round trip delay time 712 calculated by the delay time calculation unit 504 as a new minimum delay time (minimum delay time 2).

  At time T4, the round trip delay time 713 calculated by the delay time calculation unit 504 is longer than the minimum delay time (minimum delay time 2) stored in the minimum delay time storage unit 505. In this case, the minimum delay time storage unit 505 does not store the round trip delay time 713 calculated by the delay time calculation unit 504 as the minimum delay time. Further, the delay error calculation unit 506 calculates the difference between the round trip delay time 713 calculated by the delay time calculation unit 504 and the minimum delay time (minimum delay time 2) stored in the minimum delay time storage unit 505 as a delay error. Calculated as 722.

  Here, returning to FIG. 5 again, the description of the time synchronization client unit 301 is further continued.

  When the delay error calculated by the delay error calculation unit 506 is greater than a predetermined threshold, the time synchronization determination unit 507 stops the time synchronization processing by the time synchronization unit 509. On the other hand, when the delay error calculated by the delay error calculation unit 506 is equal to or less than a predetermined threshold, the time synchronization determination unit 507 causes the time synchronization unit 509 to execute time synchronization processing.

  For example, the time synchronization determination unit 507 stores information indicating the determination conditions as shown in Table 1 in advance in, for example, the storage unit 203 or the memory 202 in FIG.

表１の例では、時刻同期判断部５０７による判断の条件となる閾値は、時刻同期クライアント部３０１（又は表示システム１００）で許容される時刻の誤差である許容誤差の２倍の値に定められている。これは、ＮＴＰにおいて、図６で説明したように、往路の遅延時間ｄ１と復路の遅延時間ｄ２とに差がないと仮定して、時刻同期クライアント部３０１側の時刻ｔ０との時刻差ｃｉを算出するため、最大で遅延誤差の半分が時刻差ｃｉの誤差として生じる可能性があるためである。

In the example of Table 1, the threshold value that is a condition for the determination by the time synchronization determination unit 507 is set to a value that is twice the allowable error, which is an error in time allowed by the time synchronization client unit 301 (or the display system 100). ing. In NTP, as described with reference to FIG. 6, assuming that there is no difference between the forward delay time d1 and the backward delay time d2, the time difference ci from time t0 on the time synchronization client unit 301 side is calculated. This is because a maximum half of the delay error may occur as an error of the time difference ci for calculation.

  It should be noted that the threshold value as a judgment condition may be a value that is twice or less of the allowable error. For example, the allowable error may be set to a value that is smaller than twice due to an error, a margin, or the like. .

  The time synchronization unit 509 synchronizes the time of the time synchronization client unit 301 with the time of the time management server unit 302 by using the time difference ci calculated by the time synchronization information calculation unit 503. For example, the time synchronization unit 509 corrects the time of the time synchronization client unit 301 by adding (or subtracting) the time difference ci to the time managed by the time management unit 510.

  The time management unit 510 manages the time of the time synchronization client unit 301 by using, for example, the RTC 206 in FIG.

  The initialization unit 511 initializes the minimum delay time stored in the minimum delay time storage unit 505 as necessary, for example, when the network environment changes.

  The operation mode management unit 512 manages the operation mode setting indicating whether or not to execute the time synchronization method according to the present embodiment. For example, when the operation mode is set to be valid based on the setting information preset by the user or the like, or the setting information notified from the information terminal 102, the operation mode management unit 512 displays the time synchronization client unit 301. Then, the time synchronization method according to the present embodiment is executed. On the other hand, when the operation mode is set to invalid, the operation mode management unit 512 causes the time synchronization client unit 301 to perform time synchronization by normal NTP without executing the time synchronization method according to the present embodiment. .

  With the above configuration, for example, the time synchronization client unit 301 of the projectors 101-2 and 101-3 shown in FIG. 3 periodically transmits a time synchronization packet to the time management server unit 302 to execute the time synchronization process. .

  The projector 101 is an example of an electronic device according to the present embodiment. The electronic device according to the present embodiment includes various devices such as a display device using a liquid crystal display or the like, an audio output device, and a photographing device.

<Process flow>
Subsequently, a process flow of the time synchronization method according to the present embodiment will be described.

[First Embodiment]
FIG. 8 is a flowchart illustrating an example of time synchronization processing according to the first embodiment. In FIG. 3, the time synchronization client unit 301 included in the projectors 101-2 and 102-3 periodically executes the time synchronization process illustrated in FIG. 8, for example.

  In step S801, the synchronization packet transmission unit 501 of the time synchronization client unit 301 transmits a time synchronization packet (first time synchronization packet) to, for example, the time management server unit 302 included in the projector 101-1. As described above, the first time synchronization packet includes information on the transmission time t0 at which the first time synchronization packet is transmitted.

  In step S802, the synchronization packet receiving unit 502 of the time synchronization client unit 301 receives the time synchronization packet (second time synchronization packet) transmitted from the time management server unit 302 according to the first time synchronization packet transmitted in step S801. Packet). As described above, the second time synchronization packet includes information such as the transmission time t0, the reception time t1, and the reply time t2.

  In step S803, the time synchronization information calculation unit 503 of the time synchronization client unit 301 calculates time synchronization information using the time information included in the second time synchronization packet received by the synchronization packet reception unit 502. For example, the time synchronization information calculation unit 503 calculates the time difference ci between the time t0 ′ on the time management server unit 302 side and the time t0 on the time synchronization client unit 301 side using the above-described equation (2).

  In step S804, the delay time calculation unit 504 of the time synchronization client unit 301 uses the time information included in the second time synchronization packet received by the synchronization packet reception unit 502 and the above-described equation (1) to reciprocate. The delay time di is calculated.

  In step S805, the minimum delay time storage unit 505 of the time synchronization client unit 301 determines whether the round trip delay time di calculated by the delay time calculation unit 504 is shorter than the minimum delay time stored in the minimum delay time storage unit 505. Judging.

  When the calculated round-trip delay time di is shorter than the minimum delay time, the minimum delay time storage unit 505 stores the calculated round-trip delay time di as the minimum delay time in step S806.

  On the other hand, when the calculated round-trip delay time di is longer than the minimum delay time, the minimum delay time storage unit 505 does not update the minimum delay time and shifts the process to step S807.

  In step S807, the delay error calculation unit 506 of the time synchronization client unit 301 calculates a delay error that is a difference between the minimum delay time stored in the minimum delay time storage unit 505 and the calculated round-trip delay time di. calculate.

  In step S807, the time synchronization determination unit 507 determines whether the calculated delay error is larger than a predetermined threshold value (for example, a value that is twice the allowable error).

  When the calculated delay error is less than or equal to the threshold, the time synchronization determination unit 507 updates the last synchronization time indicating the time when the time synchronization was last performed in step S809, and in step S810, the time synchronization unit 509 Perform synchronous processing.

  On the other hand, when the calculated delay error is larger than the threshold value, the time synchronization determination unit 507 stops the time synchronization processing by the time synchronization unit 509 in step S811.

  As a result of the above processing, the time synchronization client unit 301 performs time synchronization within the allowable error range that is an allowable time error in the display system 100 or the time synchronization client unit 301, and exceeds the allowable error range. If this happens, cancel the time synchronization.

  Thus, according to the present embodiment, an electronic device (projector 101-2) that makes it easy to keep a time error within a predetermined range even in a network environment in which a difference is likely to occur between the communication forward and return delay times. , 101-3).

  Note that the processing flow shown in FIG. 8 is an example. For example, the process shown in step S804 may be executed before the process shown in step S803, or may be executed in parallel with the process shown in step S803.

[Second Embodiment]
The time synchronization process shown in FIG. 8 is effective when there is a difference between the forward delay time d1 and the backward delay time d2 of the time synchronization packet, for example, in a wireless LAN or the like. On the other hand, when there is little difference between the forward delay time d1 and the backward delay time d2 of the time synchronization packet, such as a wired LAN with a small number of connected terminals, the time synchronization by normal NTP may be sufficient.

  In the second embodiment, an example will be described in which the user can select whether to enable or disable the time synchronization processing shown in FIG. 8 by setting the operation mode.

  FIG. 9 is a diagram illustrating an example of time synchronization processing according to the second embodiment. Note that the processing in steps S801 to 803 and steps S804 to S811 in FIG. 9 is the same as the time synchronization processing according to the first embodiment shown in FIG. 8, and here, differences from the first embodiment are described. The explanation will be given mainly.

  In step S901, the operation mode management unit 512 of the time synchronization client unit 301 determines whether or not the operation mode setting indicating whether or not to execute the time synchronization method according to the present embodiment is set to be valid.

  When the operation mode setting is set to be valid, the operation mode management unit 512 sends the delay time calculation unit 504, the minimum delay time storage unit 505, the delay error calculation unit 506, the time synchronization determination unit 507, and the like to step S804. The subsequent processing is executed.

  On the other hand, when the setting of the operation mode is set to invalid, in step S902, for example, data such as the minimum delay time stored in the minimum delay time storage unit 505 is reset, and in step S810, the time synchronization unit 509 is reset. A normal time synchronization process is executed.

  With the above processing, for example, when the environment of the network 103 is bad or when there is a difference in the timing of multi-projection, the user can selectively execute the time synchronization processing according to the present embodiment. become. As a result, when the environment of the network 103 is good, by setting the operation mode to invalid, the processing in steps S804 to S809 in FIG. 9 can be omitted, and the load on the projector 101 can be reduced.

  The process shown in FIG. 9 is an example. For example, the process of step S804 may be executed before step S901, or may be executed before step S803.

[Third Embodiment]
It is desirable that the time synchronization client unit 301 initializes the minimum delay time stored in the minimum delay time storage unit 505 when the network environment is changed. This is because the value of the minimum delay time changes when the network environment changes.

  The network environment can be changed by, for example, changing the connection between the wireless LAN and the wired LAN, changing the access point of the wireless LAN, changing the connection destination of the wired LAN, the IP address, turning on the power of the projector 101, Off etc. are included.

  FIG. 10 is a flowchart illustrating an example of time synchronization processing according to the third embodiment.

  In step S1001, the initialization unit 511 of the time synchronization client unit 301 determines whether the network environment has been changed. For example, the initialization unit 511 indicates that the network environment has changed when the projector 101 is connected to a new network, the access point connected by the wireless LAN is changed, the IP address is changed, or the like. to decide.

  When the network environment is changed, the initialization unit 511 initializes the minimum delay time stored in the minimum delay time storage unit 505 (for example, sets it to the maximum value of the minimum delay time).

  In step S1003, the time synchronization client unit 301 executes the time synchronization process illustrated in FIG. 8 or FIG. 9, for example.

  With the above processing, when the network environment changes, the time synchronization client unit 301 can initialize the minimum delay time and start the time synchronization processing according to the new network environment.

(Example of multi-projection processing)
FIG. 11 is a sequence diagram illustrating an example of multi-projection processing according to an embodiment. In this process, for example, as shown in FIG. 1, a plurality of projectors 101-1 to 101-3 are used to perform multi-projection in which one projection image (moving image or still image) 106 is projected onto the projection surface 104. An overview of the process is shown. At the start of the processing shown in FIG. 11, the projectors 101-1 to 101-3 and the information terminal 102 are connected via the network 103, and the projectors 101-1 to 101- are connected to the information terminal 102. 3 destination information (IP address or the like) is set.

  In step S <b> 1101, the user performs a multi-projection operation for starting multi-projection on the information terminal 102.

  In step S1102, when the display management unit 304 of the information terminal 102 receives a multi-projection operation by the user, for example, the display management unit 304 transmits a time management server activation request for requesting to function as a time management server to the projector 101-1.

  In step S1103, the display control unit 303 of the projector 101-1 activates the time management server unit 302 to enable the function of the time management server.

  In step S <b> 1104, the display control unit 303 of the projector 101-1 transmits a completion notification indicating that the function as the time management server has been validated to the information terminal 102.

  In step S1105, the display management unit 304 of the information terminal 102 transmits, for example, a time synchronization request that instructs the projector 101-2 to synchronize the time with the time management server (projector 101-1). This time synchronization request includes destination information of the time management server (for example, the IP address, MAC address, etc. of the projector 101-1).

  In step S1106, the time synchronization client unit 301 of the projector 101-2 transmits a time synchronization packet (first time synchronization packet) to the projector 101-1 designated as the time management server.

  In step S1107, when the time management server unit 302 of the projector 101-1 receives the time synchronization packet from the projector 101-2, it returns a time synchronization packet (second time synchronization packet) to the projector 101-2.

  In step S1108, the time synchronization client unit 301 of the projector 101-2 executes time synchronization processing shown in steps S803 to S811, for example, in FIG.

  In step S1109, when the time synchronization client unit 301 of the projector 101-2 finishes the time synchronization process, the time synchronization client unit 301 transmits a completion notification indicating that the time synchronization process is completed to the information terminal 102.

  Similarly, in step S1110, the display management unit 304 of the information terminal 102 transmits, for example, a time synchronization request that instructs the projector 101-3 to synchronize the time with the time management server (projector 101-1).

  In step S <b> 1111, the time synchronization client unit 301 of the projector 101-3 transmits a time synchronization packet (first time synchronization packet) to the projector 101-1 designated as the time management server.

  In step S <b> 1112, when the time management server unit 302 of the projector 101-1 receives the time synchronization packet from the projector 101-3, it returns a time synchronization packet (second time synchronization packet) to the projector 101-3.

  In step S1113, the time synchronization client unit 301 of the projector 101-3 executes, for example, the time synchronization process shown in steps S803 to S811 in FIG.

  In step S <b> 1114, when the time synchronization client unit 301 of the projector 101-3 finishes the time synchronization process, the time synchronization client unit 301 transmits a completion notification indicating that the time synchronization process is completed to the information terminal 102.

  In steps S1115 to S1117, the display management unit 304 of the information terminal 102 transmits a projection start request for requesting the start of multi-projection to the projectors 101-1 to 101-3. In this projection start request, for example, content information for specifying the content to be projected (moving image, still image, etc.), information on the projection area for designating the area to be projected, and information on the projection start time indicating the time to start projection Etc. are included.

  In steps S1118 to S1120, the display control unit 303 of the projectors 101-1 to 101-3 starts projecting the designated area of the designated content at the projection start time.

  Through the above processing, the projectors 101-2 and 101-3 can synchronize the time with the projector 101-1, and can start projecting the designated content at the same timing.

  In addition, the projectors 101-2 and 101-3 according to the present embodiment perform time synchronization within an allowable error range that is an allowable time error in the display system 100, and when the allowable error range is exceeded, Do not synchronize time. Thereby, the display system 100 according to the present embodiment can reduce the occurrence of a time difference in the display timing between the projectors 101 even when the network environment deteriorates.

100 Display System 101 Projector (Electronic Equipment, Display Device, Computer)
101-1 projector (an example of a time management device)
101-2, 101-3 Projector (electronic equipment)
102 Information terminal (another example of a time management device)
502 synchronization packet reception unit 504 delay time calculation unit 505 minimum delay time storage unit 506 delay error calculation unit 507 time synchronization determination unit 509 time synchronization unit 511 initialization unit

JP, 2015-167341, A JP 2009-77207 A

Claims (10)

An electronic device that synchronizes time with a time management device that manages a reference time,
A synchronization packet receiver for receiving a second time synchronization packet transmitted from the time management device in response to a first time synchronization packet transmitted to the time management device;
A time synchronization unit that synchronizes the time managed by the electronic device with the reference time managed by the time management device based on the time information included in the second time synchronization packet;
A delay time calculation unit for calculating a round trip delay time required for transmission of the first time synchronization packet and transmission of the second time synchronization packet based on time information included in the second time synchronization packet; ,
A minimum delay time storage unit that stores a minimum delay time that is a minimum value of the round trip delay time;
A delay error calculation unit that calculates a delay error that is a difference between the round trip delay time calculated by the delay time calculation unit and the minimum delay time stored in the minimum delay time storage unit;
When the delay error calculated by the delay error calculation unit is greater than a predetermined threshold, a time synchronization determination unit that stops time synchronization by the time synchronization unit;
Electronic equipment having The preset threshold is:
The electronic device according to claim 1, wherein the electronic device is determined based on an allowable error that is an error in time allowed in the electronic device. The preset threshold is:
The electronic apparatus according to claim 2, wherein the value is twice the allowable error. The minimum delay time storage unit includes:
When the round trip delay time calculated by the delay time calculation unit is shorter than the minimum delay time stored in the minimum delay time storage unit, the calculated round trip delay time is stored as the minimum delay time. Item 4. The electronic device according to any one of Items 1 to 3. The electronic device is
Connected to the time management device via a network,
5. The electronic apparatus according to claim 1, further comprising: an initialization unit that initializes the minimum delay time stored in the minimum delay time storage unit when the configuration of the network is changed. The electronic device is
The electronic apparatus according to claim 1, wherein the electronic apparatus is a display device that displays an image in a predetermined display area in synchronization with a time of another display device. A plurality of display devices according to claim 6,
A display system that uses the plurality of display devices to display a predetermined image in a display area wider than each display area of the display device.   The display system according to claim 7, wherein the display device is a projector. An electronic device that synchronizes the time with a time management device that manages the reference time,
A synchronization packet receiver for receiving a second time synchronization packet transmitted from the time management device in response to a first time synchronization packet transmitted to the time management device;
A time synchronization unit that synchronizes the time managed by the electronic device with the reference time managed by the time management device based on the time information included in the second time synchronization packet;
A delay time calculation unit for calculating a round trip delay time required for transmission of the first time synchronization packet and transmission of the second time synchronization packet based on time information included in the second time synchronization packet; ,
A minimum delay time storage unit that stores a minimum delay time that is a minimum value of the round trip delay time;
A delay error calculation unit that calculates a delay error that is a difference between the round trip delay time calculated by the delay time calculation unit and the minimum delay time stored in the minimum delay time storage unit;
When the delay error calculated by the delay error calculation unit is greater than a predetermined threshold, a time synchronization determination unit that stops time synchronization by the time synchronization unit;
Program to function as. A time synchronization method by a time management device that manages a reference time and a computer that synchronizes the time,
The computer is
Receiving a second time synchronization packet transmitted from the time management device in response to the first time synchronization packet transmitted to the time management device;
Calculating a round trip delay time required for transmission of the first time synchronization packet and transmission of the second time synchronization packet based on time information included in the second time synchronization packet;
Calculating a delay error which is a difference between the calculated round trip delay time and a minimum delay time which is a minimum value of the round trip delay time;
When the calculated delay error is equal to or less than a predetermined threshold value, the computer at the reference time managed by the time management device based on time information included in the second time synchronization packet Synchronizing the time managed by
When the calculated delay error is greater than a predetermined threshold, stopping the time synchronization based on the time information included in the second time synchronization packet;
Time synchronization method including

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