Delay Time Measurement System

Abstract

To simplify a delay time measurement system because it is required that an instruction for a measurement between a video image transmission side and a video image reception side is performed and software coping with GPS time synchronization is created when installing a GPS receiver to each delay for time synchronization in order to perform a video image delay measurement between remote sites.SOLUTION: A device observes a video image of a flash of a light source photographed, transmitted, and displayed by a measured system by a light sensor, and compares the video image with a light source driving signal to measure a delay time. Instead of a reference signal generator used for the measurement at a proximity site, a signal of which a time as 1 PPS generated from a GPS receiver of each installation is synchronized at a remote site is used. A logic signal that is surely synchronized with an absolute time at 50% of a duty ratio generated on the basis of the 1 PPS signal is used on a video image transmission side and a video image reception side. By limiting a period of the flash to 1 second, a delay measurement can be extremely easily realized by introducing a GPS to two sites without change of software on the assumption of an only operation of a reference signal generator used for the measurement at the proximity site without GPS.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] This invention relates to a delay time measurement system that uses a GPS (Global Positioning System) to accurately measure the time required for a series of operations to be performed on a measurement target that captures, transmits, and displays images, etc. between remote locations. Measurement targets are not limited to images, but can also include audio and haptics. [Background technology]

[0002] There are many ways to measure video delay time, including inserting a timestamp, capturing and displaying a clock, and measuring the round trip time using the ICMP protocol on an IP network.

[0003] In the method using timestamps, the video sending side sends information with an accurate time stamp along with the video signal, which is then transmitted through the system under test and analyzed at the receiving side. For example, details of this method are described in Patent Document 1. However, this method cannot measure the delay of the video cameras and displays included in the system under test, and can only measure the delay time of a part of the system. Furthermore, a signal with a timestamp must be inserted at the video sending side in addition to the original video signal and extracted at the receiving side, making the measurement system complicated.

[0004] A method for capturing and displaying an image of a clock is described in, for example, Patent Document 2, in which an image of the clock is captured by a video camera in the system under test, and the image displayed on the display of the system under test after transmission is compared with the image of the clock at that time to calculate the delay time. While this system can measure delay times including the video camera and display, it has the problem of poor accuracy because it cannot accurately capture changes in the clock display.

[0005] Measurements using the ICMP protocol on IP networks, i.e., the so-called ping command, are widely used, and there is no need to cite any literature on this. However, this only targets round-trip delay time, and the measurement is limited to transmissions over IP networks. Furthermore, it cannot measure delays including those from video cameras and displays.

[0006] Another method is shown in Non-Patent Document 1. In this method, a light source blinks using a measuring device, and the image is captured and transmitted by a video camera in the system under test. The blinking image displayed on a display is then converted into an electrical signal by an optical sensor, and the delay time is measured from the response.

[0007] Figure 1 shows the configuration. In Figure 1, 1 is a light source, such as a light-emitting diode (LED), and 2 is an optical sensor, such as a photodiode (PD). 3 is a reference signal generator, which outputs a predetermined rectangular wave under the control of controller 7. 4 is a light source driver, which generates a signal to drive light source 1 from the signal from reference signal generator 3. 5 is a trigger signal generator, which inputs the signal from reference signal generator 3 and generates a signal to be applied to waveform measurement unit 6. The timing of signal changes from light source driver 4 and trigger generator 5 is the same. Waveform measurement unit 6 measures the waveforms of the signal from optical sensor 2 and the signal from trigger generator 5. The waveform acquired by waveform measurement unit 6 is sent to controller 7, where it is analyzed and the delay time is calculated. Controller 7 is, for example, a personal computer, and the delay time calculation result is displayed on its display. 10 is the system under test, which includes a video camera 11, a video transmission system 12, and a display 13.

[0008] This operation is shown in the time chart of Figure 2. When the light source drive signal, i.e., the trigger signal, is at low level, light source 1 is turned off, and when it is at high level, the light source is turned on. The output of video camera 11 of system under test 10, which captures an image of the light source, is displayed on display 13 via video transmission system 12. The delay time of this operation is a delay in the light intensity signal output from optical sensor 2, as shown in Figure 2, and the delay time can be measured by analyzing it in controller 7, such as the time indicated by T1 when light source 1 goes from off to on, and the time indicated by T2 when it goes from on to off.

[0009] The configuration in Figure 1 does not use timestamps, so the video signal under test is left untouched, and it can measure all delays from the video camera to the display. Furthermore, it uses two values, the on / off state of the light source, so it can simply calculate delay time. Unlike the ICMP protocol, it can evaluate one-way delays in any video transmission system, not limited to IP networks.

[0010] The delay time measurement system in Figure 1 is based on the premise that the video camera 11 and display 13 of the system under test 10 are close to each other and that the distance is such that the measurement signals can be connected appropriately via a cable. However, if the video camera 11 and display 13 of the system under test 10 are installed in remote locations and you want to measure the delay time between them, it is common to use GPS to synchronize the time, as shown in Figure 3.

[0011] In Figure 3, GPS receiver 21 and GPS receiver 31 are installed at different locations. When receiving signals from a location with good signal reception, the GPS receiver's time accuracy typically achieves an error of approximately ±10 nanoseconds relative to absolute time. On the other hand, if the system under test has a video signal frame rate of, say, 60 Hz, the period should preferably be shorter than 16.7 milliseconds. The signal from the GPS receiver has sufficient accuracy. Based on the signal from the GPS, controllers 23 and 24 control reference signal generators 22 and 32 to generate predetermined square waves. The output of reference signal generator 22 drives light source 2 via light source driver 4. Meanwhile, the output of reference signal generator 32 is applied to waveform measurement unit 6 via trigger generator 5. The outputs of reference signal generator 22 and 32 are precisely synchronized by the GPS function, and are considered identical signals generated by a single reference signal generator. This configuration achieves the same operation as the timing chart shown in Figure 2, enabling delay measurements between remote locations. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Patent No. 3892844 [Patent Document 2] Patent No. 5553409 [Non-patent literature]

[0013] [Non-Patent Document 1] Taro Ogawa and Hiroyuki Matsuura, "Zero-Delay Optical Video Transmission Technology and Its Applications," Large Display & Digital Signage Overview 2020, pp. 12-22, Japan Social Systems Laboratory, 2020. Summary of the Invention [Problem to be solved by the invention]

[0014] 3, controllers 23 and 33 must communicate with each other and control the entire measurement system to prevent discrepancies in their operations. This communication can be achieved, for example, using the Internet, but it is cumbersome. Furthermore, it is necessary to have reference signal generators 22 and 32, respectively, and the control of these generators is also cumbersome.

[0015] Furthermore, when measuring delay times at remote locations, the configuration shown in Figure 3 is used, and when measuring delay times at short distances, the configuration shown in Figure 1 is used, but each requires appropriate controller control software. This requires both hardware and software switching depending on the distance, which is cumbersome. It would be desirable to be able to measure delay times even when synchronized with GPS by using the same software used for short-distance measurements without modification, without creating software compatible with GPS. [Means for solving the problem]

[0016] In order to solve these problems, a device is provided which turns on and off a light source installed at a first location using a light source drive signal, converts the light source image into a video signal using a video camera in the system under test, transmits the video signal, and then converts the image of the light source displayed on a display of the system under test into an electrical signal using an optical sensor at a second location, and measures the time difference between the change in the light source drive signal and the electrical signal from the optical sensor, When the first point and the second point are located far apart, a first GPS receiver is installed at the first point and a second GPS receiver is installed at the second point, and the signals from the first GPS receiver and the second GPS receiver are used as the time reference at each point; when the first point and the second point are located close to each other, no GPS receivers are used, and the signal from a single reference signal generator connected by electrical wiring is used as the time reference; Even when the first and second GPS receivers are used, a controller that controls the entire system is installed only at the second location, and control of time synchronization at the first location is not performed by instructions from the controller via communication, but is performed solely by signals from the first GPS receiver installed at the first location; The controller software uses the same software as that which operates without signals from the first and second GPS receivers, and establishes a delay time measurement system that measures a predetermined time difference. [Effects of the Invention]

[0017] Because the first GPS receiver and the second GPS receiver are configured to appear as a single reference signal generator, it is easy to switch between a configuration using GPS when measuring delay times between distant locations and the configuration shown in Figure 1 when measuring delay times over short distances without GPS. Furthermore, there is no need to switch software. The same software used for short-distance measurements can be used without modification when using GPS to measure delay times. Furthermore, since the controller does not issue instructions for measurement to a remote location, i.e., no communication for measurement is performed from point 2 where the controller is installed to point 1 where the controller is not installed, a simple system can be realized. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a diagram illustrating a conventional example of a delay time measurement system that does not use GPS. [Figure 2] 2 is a timing chart showing the operation of FIG. 1; [Figure 3] 1 is a diagram illustrating a conventional delay time measurement system using GPS. [Figure 4] 1 is a diagram showing a first embodiment of the present invention; [Figure 5] FIG. 4 is an explanatory diagram of when GPS is used. [Figure 6]FIG. 10 is a diagram illustrating a second embodiment of the present invention. [Figure 7] FIG. 10 is a diagram illustrating a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION [Example]

[0019] A first embodiment is shown in Figure 4. Here, the output signals of GPS receiver 21 and GPS receiver 31 are signals with an accurate one-second period known as 1PPS (Pulse Per Second), and the timing of their changes is synchronized with the absolute time to within an error of ±10 nanoseconds. This 1PPS signal is often output as standard from components and devices sold commercially as ordinary GPS receivers. However, the output of GPS receiver 21 is configured to output a signal with a predetermined duty cycle, for example, a 50% duty cycle. If the components used do not have this, the above can be achieved by adding appropriate circuitry.

[0020] At the location where the video camera 11 of the system under test 10 is installed, the output of the GPS receiver 21 is connected to the light source driver 25 via the changeover switch 24. In explaining the operation of measuring a remote location using GPS, the changeover switch 24 is set to connection A. By doing so, the light source 1 repeatedly turns on and off with a duty cycle of 50% at one-second intervals precisely synchronized with absolute time.

[0021] At the point where the display 13 of the system under test 10 is installed, the output of the GPS receiver 31 is connected to the trigger generator 35 via the changeover switch 34. The changeover switch 34 is set to the A connection, and a trigger signal with a duty cycle of 50% is output from the trigger generator 5 at a 1-second period synchronized with the blinking of the light source. The changeover switch 34 is set to the A connection, and the reference signal generator 3 is not used for measurement. Similarly, in Figure 4, the changeover switch 24 is set to the A side, so the output of the reference signal generator 3 is not used by the changeover switch 24, and no wiring is required.

[0022] The waveform measurement unit 5 receives signals from the optical sensor 2 and the trigger generator 5, sends the data to the controller, and analyzes the waveform and measures the delay time in the same way regardless of whether GPS is present or not.

[0023] Figure 5 is an explanatory diagram of the first embodiment, which is the same as Figure 4 except that switches 24 and 34 are set to position A and the unused reference signal generator 3 is removed. Instead of reference signal generator 3, GPS receiver 21 and GPS receiver 31 are used, and it can be seen that, despite the remote location, the system operates as if it were using a signal from a single reference signal generator. In this case, the signal from the GPS receiver is based on a 1PPS signal, and operates in no way differently from a reference signal generator with a 1-second cycle and a 50% duty cycle. Software operation with a 1-second cycle is assumed to be realized in a system without GPS, and the control software for controller 7 can be used without modification even when GPS is not used. This is a significant advantage.

[0024] Next, we will describe the case where GPS is not used and a video camera and display are installed in close proximity. In this case, selector switch 24 in Figure 4 is connected to side B, and selector switch 34 is also connected to side B. In this case, the outputs of GPS receiver 21 and GPS receiver 31 are not used. This results in exactly the same connection relationship as in Figure 1, and its operation is as described above, allowing the desired delay time to be measured. These selector switches 24 and 34 are not only mechanical switches, but also have low switching frequency, so the same can be achieved by simply plugging and unplugging the connector. The same applies to the selector switches below. [Example]

[0025] In FIG. 6 showing the second embodiment, two light source driving units and two trigger generators are depicted, and the positions of the changeover switches are different from those in FIG. 4 showing the first embodiment.

[0026] At the point where the video camera 11 of the system under test 10 is installed, the output of the GPS receiver 21 is connected to a changeover switch 26 via a light source driver 25. If the changeover switch 26 is connected to side A, the light source will repeatedly turn on and off with a duty cycle of 50% in one-second cycles in accordance with the 1PPS signal from the GPS receiver 21.

[0027] At the point where the display 13 of the system under test 10 is installed, the output of the GPS receiver 31 is connected to a changeover switch 36 via a trigger generator 35. The changeover switch 36 is set to connection A, and a trigger signal with a duty cycle of 50% is output from a trigger generator 37 in a 1-second cycle synchronized with the blinking of the light source. The changeover switch 36 is set to connection A, and the signal from the reference signal generator 3 via the trigger generator 3 is not used for measurement. Similarly, in Figure 6, the changeover switch 26 is set to connection A, and therefore the signal from the output of the reference signal generator 3 via the light source driver 4 is not used by the changeover switch 26, and therefore no wiring is required.

[0028] In FIG. 6, the waveform measurement unit 5 receives a signal from the optical sensor 2 trigger generation 37, sends the data to the controller, and analyzes the waveform and measures the delay time in the same way regardless of whether GPS is present or not.

[0029] In this way, if switches 26 and 36 are set to side A and unused reference signal generator 3, light source driver 3, and trigger generator 3 are deleted and rearranged, the result will be the same as Figure 5. GPS receiver 21 and GPS receiver 31 are used in place of reference signal generator 3, etc., and it can be seen that even in this case, despite being in remote locations, they are operating as if they were using signals from a single reference signal generator.

[0030] Next, we will describe the case where GPS is not used and the video camera and display are installed in close proximity. In this case, the selector switch 26 in Figure 6 is connected to side B, and the selector switch 36 is also connected to side B. In this case, the outputs of the GPS receiver 21, light source driver 25, GPS receiver 31, and trigger generator 37 are not used. This results in exactly the same connection relationship as in Figure 1, and its operation is as described above, allowing the desired delay time to be measured. [Example]

[0031] A third embodiment of the present invention is shown in Figure 7. This is a GPS module that houses the GPS receiver, light source driver, and trigger generation in a single housing. That is, GPS module 28 consists of GPS receiver 21, light source driver 25, and trigger generation 27. Only the output of light source driver 25 is connected to switch 26, and the output of trigger generation 27 is not used. Similarly, GPS module 38 consists of GPS receiver 31, light source driver 35, and trigger generation 37. Only the output of trigger generation 37 is connected to switch 36, and the output of light source driver 35 is not used. The operation in this case is the same as that already described. Although the number of blocks increases and it may seem more complicated, the size of each individual circuit block is small and not a problem. For example, the light source driver is a single transistor, and the trigger is generated by a voltage divider circuit using two resistors. By configuring it in this way, GPS module 28 and GPS module 38 are the same, so users do not need to use them differently, and manufacturers also have the great advantage of not having to manufacture and stock separate modules.

[0032] The explanation so far has been about measuring video delay. The object of measurement is not limited to video; it can also be audio, for example. In this case, what is turned on and off is the sound from the speaker instead of the light source, a microphone instead of a video camera in the system under test, and a speaker instead of a display. The microphone receives the sound on the measurement system side. In this case too, the present invention can be applied in the same way, converting the audio into an electrical signal, detecting it, and converting it into an electrical signal of audio intensity.

[0033] Haptics can also be measured. Haptics is a technology that obtains tactile feedback by applying force, vibration, movement, etc. to the user. In other words, the system under test has a vibration-sensing sensor instead of a video camera, and a vibration-generating actuator instead of a display. On the measurement side, an actuator that generates vibrations is installed instead of a light source, and a vibration-sensing sensor is installed instead of an optical sensor, and the intensity of the vibrations is used to measure delay. [Explanation of symbols]

[0034] The symbols in FIGS. 1 to 7 are as follows: 1 --- Light source 2 --- Optical sensor 3 --- Reference signal generator 4 --- Light source driver 5 --- Trigger occurs 6 --- Waveform measurement section 7 --- Controller 10 --- System under test 11 --- Video camera 12 --- Video transmission system 13 --- Display 21 --- GPS receiver 22 --- Reference signal generator 23 --- Controller 24 --- Changeover switch 25 --- Light source driver 26 --- Changeover switch 27 --- Trigger occurs 28 --- GPS module 31 --- GPS receiver 32 --- Reference signal generator 33 --- Controller 34 --- Changeover switch 35 --- Light source driver 36 --- Changeover switch 37 --- Trigger occurs 38 --- GPS module

Claims

1. An apparatus for driving an actuator installed at a first point on / off with a driving electric signal, sensing and transmitting the signal in a system under test, and then converting a physical quantity output from a second point of the system under test into an electric signal by a sensor, and measuring the time difference between the change in the driving electric signal and the change in the electric signal from the sensor, comprising: When the first point and the second point are located far apart, a first GPS receiver is installed at the first point and a second GPS receiver is installed at the second point, and the signals from the first GPS receiver and the second GPS receiver are used as the time reference at each point; when the first point and the second point are located close to each other, no GPS receivers are used, and the signal from a single reference signal generator connected by electrical wiring is used as the time reference; Even when the first and second GPS receivers are used, a controller that controls the entire system is installed only at the second location, and control of time synchronization at the first location is not performed by instructions from the controller via communication, but is performed solely by signals from the first GPS receiver installed at the first location; The controller software is the same as that which operates without signals from the first and second GPS receivers, and is used to measure a predetermined time difference.

2. The delay time measurement system according to claim 1, wherein the system under test comprises a video camera, a video transmission unit, and a display, the actuator is a light source, and the sensor is an optical sensor.

3. The delay time measurement system according to claim 1, wherein the system under test comprises a first microphone, an audio signal transmission unit, and a first speaker, the actuator is a second speaker, and the sensor is a second microphone.

4. The delay time measurement system according to claim 1, wherein the system under test comprises a first vibration sensor, a vibration signal transmission unit, and a first vibration actuator, the actuator being a second vibration actuator, and the sensor being a second vibration sensor.

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