Delay Time Measurement System

Abstract

To appropriately and efficiently obtain light sensor output levels at the time of blackout and at the time of lighting of a light source before video delay measurement and, furthermore, appropriately cope with a relation between a repeated measurement period and an operation period of a system to be measured.SOLUTION: There is used a delay time measurement system that before delay time measurement, makes a light source repeat OFF / ON and acquires a first signal value from a light sensor before timing of transition from OFF to ON and a second signal value from the light sensor after lapse of a previously set guard time after the transition and, at measurement of a time difference, calculates a delay time from timing of variation of the light source and timing at which a signal from the light sensor crosses a threshold on the basis of the first and second signal values. There is used a delay time measurement system that at the time of the delay time measurement, makes a repeating period at the time of the light source repeating OFF and ON be non-integral multiple of operation repeating of a system to be measured or determined to be a random number.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] This invention relates to a delay time measurement system that accurately measures the time required to perform a series of operations on a device under test that captures, transmits, and displays images, etc. It provides a means to determine the binary values ​​of the image brightness changes, and measures the delay time based on the threshold value determined from these values. The delay time measurement targets not only images but also audio and haptics. [Background technology]

[0002] There are many examples of methods for measuring video delay time, including inserting a timestamp, capturing and displaying a clock, and measuring the round-trip time using ICMP (Internet Control Message Protocol), one of the protocols for IP (Internet Protocol) networks.

[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 time that occurs inside the video camera or display 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, which makes 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 ICMP, one of the IP network protocols, 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 target is limited to transmission over IP networks. Furthermore, it cannot measure delays including those from video cameras and displays.

[0006] Another method is a delay time measurement system as shown in Non-Patent Document 1 and Non-Patent Document 2. This method involves using a video camera in the system under test to capture and transmit images of a light source that is blinking using a measuring device, converting the blinking image shown on a display into an electrical signal using an optical sensor, and measuring the delay time from the response.

[0007] A block diagram is shown in Figure 1. In Figure 1, 1 denotes a light source, such as a light-emitting diode (LED), and 2 denotes an optical sensor, such as a photodiode (PD). 3 denotes a reference signal generator, which outputs a predetermined rectangular wave under the control of a controller 7. 4 denotes a light source driver, which generates a signal to drive the light source 1 from the signal from the reference signal generator 3. 5 denotes a trigger signal generator, which inputs the signal from the reference signal generator 3 and generates a signal to be applied to a waveform measurement unit 6. The timing of signal changes from the light source driver 4 and the trigger generator 5 is the same. The waveform measurement unit 6 measures the waveforms of the signals from the optical sensors 2 and 5 and the signal from the trigger generator 5. The waveforms acquired by the waveform measurement unit 6 are sent to the controller 7, where they are analyzed and the delay time is calculated. The controller 7 is, for example, a personal computer, and displays the delay time calculation results on its display unit (not shown). 10 denotes a 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, light source 1 is turned on. The output of video camera 11 of system under test 10, which captures an image of light source 1, 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] In Figure 2, the optical signal strength signal level when the LED image on the display 13 is on is Von, and the optical signal strength signal level when it is off is Voff. The threshold voltage Vth is determined from these values, and when the LED image changes from off to on, the time from when the trigger signal changes to when the optical signal strength signal exceeds Vth is measured.

[0010] The configuration in Figure 1 does not use timestamps, so the video signal of the system under measurement is left untouched, and it is possible to measure all delays from the video camera 11 to the display 13. Furthermore, it uses the binary value of on / off of the light source 1, so it is possible to simply calculate the delay time. Unlike the ICMP protocol, it is not limited to transmission using an IP network, and can evaluate the one-way delay time in any video transmission system. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent No. 3892844 [Patent Document 2] Patent No. 5553409 [Non-patent literature]

[0012] [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. [Non-patent document 2] Hiroyuki Matsuura and Taro Ogawa, "Development of Transmission Technology for Zero Latency of 4K / 8K Video," Optical Circuit Implementation and Device Development for Next-Generation High-Speed ​​Communications, pp. 614-628, Information Technology Association, 2022. Summary of the Invention [Problem to be solved by the invention]

[0013] Before measuring the delay time, it is necessary to determine Von and Voff in Figure 2. These vary depending on the relative positions of the light source 1 and video camera 11, the relative positions of the display 13 and optical sensor 2, and the conditions of the system under test 10. Therefore, it is necessary to know Von and Voff beforehand before measurement.

[0014] A simple way to find Von and Voff is to (a) measure the light intensity signal with light source 1 off and use this as Voff, and (b) measure the light intensity signal with light source 1 on and use this as Von, as shown in Figure 3. The above method works when the light intensity signal is limited to two values, off and on, but in reality it can have complex characteristics that can take on intermediate values ​​where fast and slow changes overlap. When trying to measure the delay time for a fast change, the static method shown in Figure 3 can only find the value after all fast and slow changes have finished.

[0015] It is also necessary to determine measurement parameters that match the video delay time of the object under test, such as the repetition time for turning light source 1 on and off, and the data recording time for measurement. Furthermore, since the actual light intensity signal is superimposed with noise due to various factors, parameters for removing this noise must be determined. To achieve this, a prescan is performed before the actual delay time measurement, in which waveform data is acquired in advance by repeatedly turning the light on and off. Performing this process separately from the process for determining Von and Voff is time-consuming. This concludes the first challenge.

[0016] The second issue is that even if the Von and Voff values ​​are obtained appropriately, if the system under test contains repetitive operational elements, errors will occur unless the synchronization relationship with the measurement side is handled appropriately. Specifically, errors of about one video frame may occur. In other words, if the measurement repetition interval is very close to an integer multiple of the measurement operation repetition rate of the system under test, the delay measurement results will fluctuate little from repetition to repetition, and may be biased toward either small or large. The margin of error is one frame, and cannot be ignored when evaluating low-latency video transmission systems. [Means for solving the problem]

[0017] An apparatus for driving an actuator installed at a first location on / off with a driving electric signal, sensing and transmitting the output of the actuator in a system to be measured at the first location, converting a physical quantity output from the system to be measured at a second location into an electric signal by a sensor installed at the second location, and measuring a time difference between a change in the driving electric signal and a change in the electric signal from the sensor, comprising: Prior to measuring the time difference, the driving electric signal is controlled so that the actuator alternates between an off state and an on state; a first value Voff of the electrical signal from the sensor before the timing of the actuator changing from an off state to an on state; A second value Von of the electrical signal from the sensor after a predetermined guard time has elapsed after the timing is acquired; In measuring the time difference, a delay time measurement system is used that is characterized by calculating the delay time from the difference between the timing of the change in the drive electrical signal of the actuator and the timing at which the electrical signal coincides with a threshold value based on a first value Voff of the electrical signal and a second value Von of the electrical signal.

[0018] When measuring the time difference, a delay time measurement system is used in which the repetition period when the actuator periodically repeats the off state and the on state is set to a non-integer multiple of the operation repetition period of the system under test or is determined by a random number. [Effects of the Invention]

[0019] Before measuring the delay time, the sensor is repeatedly switched between the off and on states, and electrical signals before and after the change are obtained to obtain Voff and Von, thereby obtaining the light intensity signal value in use, i.e., the value related to the fast signal change mentioned above.

[0020] Voff and Von can be determined simultaneously with the pre-scan that determines the measurement parameters according to the video delay time of the object under test, reducing the complexity and improving the efficiency of the preparatory work before measurement.

[0021] In the delay time measurement process after Von and Voff have been properly obtained, even if the system under test has repetitive operational elements, the measurement repetition interval is set to a non-integer multiple of the operational repetition interval of the system under test, or is determined by a random number. This prevents the measurement results from being biased toward short or long values, and by using the average value of the repeatedly measured delay time values, an appropriate numerical value can be obtained. [Brief explanation of the drawings]

[0022] [Figure 1]1 is a general diagram illustrating a delay time measurement system that is the subject of this specification. [Figure 2] 2 is a timing chart showing the operation of FIG. 1; [Figure 3] 1 is a diagram illustrating conventional calibration data acquisition. [Figure 4] 1 is a diagram showing a first embodiment of the present invention; [Figure 5] FIG. 10 is an explanatory diagram illustrating the effect of the first embodiment. [Figure 6] FIG. 1 is a flowchart of a first embodiment. [Figure 7] 1 is a general diagram for measuring delay times of a plurality of physical quantities. [Figure 8] 8 is a timing chart showing the operation of FIG. 7. [Figure 9] FIG. 10 is a diagram illustrating a second embodiment of the present invention. [Figure 10] FIG. 10 is a first explanatory diagram for explaining a delay measurement operation. [Figure 11] FIG. 10 is a second explanatory diagram for explaining the delay measurement operation. [Figure 12] FIG. 10 is a third explanatory diagram for explaining the delay measurement operation. DETAILED DESCRIPTION OF THE INVENTION [Example]

[0023] The timing of the first embodiment is shown in Figure 4. This is done by turning light source 1 off (off state) and on (on state) in sequence and repeating this process before measuring the delay time. The value of the trigger signal that drives light source 1 is Vlow when light source 1 is turned off and Vhigh when light source 1 is turned on. Before the transition from Vlow to Vhigh, light source 1 is off, and the display 13 of the system under test is also off at that time. The level of the light intensity signal from optical sensor 2 obtained before the transition is obtained and is taken as Voff, the value for the off state.

[0024] The display 13 does not immediately turn on after the value of the trigger signal that drives the light source 1 transitions from Vlow to Vhigh. After a preset guard time Tguard has elapsed, the level of the light intensity signal from the optical sensor 2 is acquired and set to Von, which is the value for the on state.

[0025] The threshold value Vth is determined from Voff and Von. For example, the threshold value Vth is set to (Voff+Von) / 2, which is the midpoint (50%) between on and off. As will be described later, Voff and Von may be weighted to determine Vth, or different values ​​may be used for off → on and on → off. When measuring the delay time, the delay time is calculated from the timing of the change in light source 1 and the timing when the light intensity signal crosses this threshold.

[0026] FIG. 5 is a diagram illustrating one of the effects of the first embodiment. In an actual system under test, changes in the light intensity signal may occur in which slow changes are superimposed on fast changes. This is the situation where, for example, the characteristics of a sensor device or display device change gradually due to temperature changes. Since the changes perceived by human vision are the fast changes, in the example shown in the figure, it is desirable to use the value of the light intensity signal Von after the fast change has ended after Tguard has elapsed. The Von value shown in FIG. 5 is more desirable than the Von value after a steady state has been reached as shown in FIG. 3. The same is true for Voff, which is not shown in the figure.

[0027] Figure 6 shows a flowchart for measuring delay time using this embodiment. First, the parameters are initialized. The parameters here refer to the cycle when light source 1 is repeatedly blinked and the recording time when acquiring the waveform. Next, light source 1 begins blinking, and after at least one cycle has passed, the output of light sensor 2 when the light is off is acquired and taken as Voff. After the time Tguard has passed since light source 1 was turned on, the output of light sensor 2 when it was on is acquired and taken as Von. In practice, Voff and Von can be calculated by measuring the output of light sensor 2 continuously as a waveform in chronological order, and then processing it in controller 7.

[0028] The obtained Von, Voff, and waveforms are displayed in an appropriate manner, and a human judges whether they are correct or not. Alternatively, an equivalent algorithm can be created and the judgment can be made automatically. If the changes are as expected, that's fine. If the situation is unexpected, modify the parameters, the settings of the system under test, and the positions of light source 1 and optical sensor 2 in the measurement system, and repeat the process. If there are no problems, perform the delay time measurement as shown in Figure 2 and display it as appropriate. When displaying the results, it is a good idea to display not only the delay time values ​​(described below) but also the waveforms obtained during measurement. Furthermore, displaying the raw data waveform and the waveform obtained by moving average on the time axis to remove noise simultaneously will give a better understanding of the system's operating status.

[0029] The above explanation has been given on how to calculate Voff and Von when the light source 1 changes from off to on. In exactly the same way, when the light source 1 changes from on to off, it is also possible to calculate the light intensity level Von' when it is on and the light intensity level Voff' when it is off. However, it is also possible to simplify this so that Voff' = Voff and Von' = Von. [Example]

[0030] In the first embodiment, the measurement target was described as video delay time. Other measurement targets besides video include sound and haptics. Figure 7 shows a configuration that can simultaneously measure multiple physical quantities.

[0031] If sound is the target, a sound source 41 is driven by a sound source driver 44 instead of the light source 1 used in the case of video. Control is performed to determine whether or not to generate a sound wave with a frequency of, for example, 1000 Hz according to the input trigger signal. The system under test 10 senses the sound with a microphone 45 and drives a speaker 47 via an audio transmission system 46. The sound from the speaker 47 is sensed by a microphone 42 in the measurement system, and in order to determine its intensity, the signal is subjected to detection processing, such as full-wave rectification and passing through a low-frequency filter, in a processing circuit 43, and then connected to the waveform measurement unit 6 as an audio intensity signal.

[0032] In the case of haptics, the physical quantity of interest may be vibration or displacement. When the haptics is vibration, it is similar to the audio described above, and here the physical quantity of interest is exemplified as displacement. In the case of displacement, instead of light source 1 as in the case of video, a displacement source 51 is driven by a displacement source driver 54. System under test 10 senses with displacement sensor 55 and drives displacement source 57 via displacement transmission system 56. The displacement from displacement source 57 is sensed by displacement sensor 52 of the measurement system and connected to waveform measurement unit 6 as a displacement intensity signal.

[0033] The time chart for measuring delay time is shown in Figure 8. For video, the delay time from lights off to lights on is represented as Tv1, and the delay from lights on to lights off is represented as Tv2. Similarly, for audio, the delay time from no audio to audio on is represented as Ts1, and the delay from audio on to no audio on is represented as Ts2. Furthermore, for haptics, the delay time from no displacement to displacement on is represented as Th1, and the delay from displacement on to no displacement on is represented as Th2.

[0034] The above is a general explanatory diagram, and based on this, a time chart for a second embodiment of the present invention is shown in Figure 9. Video has been described in the first embodiment. For audio, data before and after the trigger signal changes from Vlow to Vhigh is acquired as a waveform to obtain Voff', the value when there is no sound, and Von', the value when there is sound. The guard time in this case is Tguard' for audio. The same is true for haptics, where data before and after the trigger signal changes from Vlow to Vhigh is acquired as a waveform to obtain Voff", the value when there is no displacement, and Von", the value when there is displacement. The guard time in this case is Tguard" for displacement.

[0035] As a variation, depending on the system under test 10, the input and output of the transmission system 59 of the system under test may not necessarily be the same. For example, the system under test may input a displacement and output light, i.e., pressing a switch causes a lamp to light up. Another example is a system that inputs video and issues an audible warning. In this case, the present invention can also be applied to find each Voff and each Von. Thus, the present invention is applicable even when what the system under test senses and what it outputs are different.

[0036] This section describes the details of measuring delay time using Voff and Von. When measuring delay time, measurements are repeatedly taken using the same parameters, and the resulting data is statistically processed to quantify the delay time. Care must be taken when handling measurement results, especially when the object being measured has periodic operating elements. As a concrete example, in a video transmission system, a video camera 11 typically captures and transmits a fixed number of frames of data per second. For example, while capturing 60 frames per second, it is common to sequentially scan the target screen rather than capturing them all at once. A schematic diagram is shown in Figure 10. This is what is known as raster scanning, and the scanning begins in the upper left corner of Figure 10. Line 1 is scanned horizontally, and when it reaches the right edge, line 2 is scanned horizontally from the left edge. This scanning is repeated, and when it reaches the bottom right, it goes back to the top right and repeats 60 times per second.

[0037] At this time, there is a difference between the timing when light source 1 lights up and the timing when it is scanned; sometimes it is sampled immediately after lighting, but in the worst case, it is sampled about one frame later. Because the system under test and the delay time measurement system described here operate asynchronously, it is not clear whether the error for one frame will appear as a nearly constant value or whether it will shift with each repetition. Therefore, the repetition period is intentionally shifted so that it is not an integer multiple of the frame rate. The period of reference signal generator 3 is controlled under the control of controller 7.

[0038] This is shown in Figure 11. The light intensity signal (1) changes quickly when scanning is performed immediately after light source 1 is turned on. The start of scanning after lighting is delayed as shown in (2), (3), (4), etc. The state (N) is the state where the time from lighting to scanning is the slowest, and then it returns to (1). As a numerical example, let's assume that the imaging frame rate of the system under test is 60 frames per second, meaning that the frame repetition time is 1 / 60 seconds, and the delay time measurement is repeated 1.01 seconds. From the state of the first delay time measurement, The timing of the second delay measurement is 1.01 ÷ (1 / 60) = 60.6 → 0.6 frame difference The timing of the third delay measurement is 2.02 ÷ (1 / 60) = 61.2 → 0.2 frame difference The timing of the fourth delay measurement is 3.03 ÷ (1 / 60) = 61.8 → 0.8 frame difference The timing of the fifth delay measurement is 4.04 ÷ (1 / 60) = 62.4 → 0.4 frame difference The timing of the sixth delay measurement is 5.05 ÷ (1 / 60) = 63.0 → 0.0 frame offset This process is repeated. We can see that this systematic frame delay occurs evenly between 0 and less than 1. Furthermore, if we add a fraction to the number of times the delay time is measured, the distribution becomes even finer.

[0039] By intentionally varying the timing of the change by shifting the repetition period in this way, it is possible to eliminate bias in the influence of the frame rate. If the shift is not intentionally done, the delay time measurement results may happen to be biased towards the fast or slow side.

[0040] In the above example, we made the delay time a non-integer multiple to prevent the delay time measurement results from being biased towards the fast or slow side, but it is also possible to add dither to the repeat period so that the next repeat time varies randomly. If the repeat is performed a sufficient number of times, it is possible to prevent the delay time measurement results from being biased towards the fast or slow side.

[0041] When displaying the results, statistical processing is performed on the repeated results to display, for example, the average, minimum, and maximum values. The minimum value corresponds to (1) in Figure 11, and the maximum value corresponds to (N) in Figure 11. In other words, in the time axis direction (horizontal direction), three numbers are obtained when the light is off → on, and three numbers are obtained when the light is on → off.

[0042] Furthermore, three values ​​are possible in the amplitude direction (vertical direction). When Voff is 0% and Von is 100%, one way of thinking is to set the threshold Vth for determining a change to, for example, the median value of 50%. However, if even the slightest change is to be recognized as a change, then it would be better to set Vth = 20% when the light goes from off to on, and Vth = 80% when the light goes from on to off. Conversely, if a change is only recognized when there is a complete change, then Vth = 80% when the light goes from off to on, and Vth = 20% when the light goes from on to off. Furthermore, although larger and smaller Vths are also possible, these values ​​are used as examples because noise from various factors may be superimposed.

[0043] When displaying the results, for example, the 18 numerical values ​​shown in Figure 12 are displayed on a display attached to the controller 7. The nine circular points represent when the light is off and when it is on, and the nine triangular points represent when it is on and when it is off. Each of the nine points is one of three types: {Vth=20%, Vth=50%, Vth=80%} x three types: {minimum, average, maximum}. The measurer can decide which of the displayed numbers to use depending on the application and how changes are recognized. Because there are so many numbers, it is effective to make each of the nine points easier to see by instructing the measurer to display them larger, using a different text color, or changing the background color. [Explanation of symbols]

[0044] The symbols in FIGS. 1 to 12 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 41 --- Sound source 42 --- Microphone 43 --- Processing circuit 44 --- Sound source drive unit 45 --- Microphone of the system under test 46 --- Audio transmission system 47 --- Speaker of the system under test 51 --- Displacement source 52 --- Displacement sensor 54 --- Displacement source drive unit 55 --- Displacement sensor of the system under test 56 --- Displacement transmission system 57 --- Displacement source of the system under test 59 --- Transmission system of the system under test

Claims

1. An apparatus for driving an actuator installed at a first location on / off with a driving electric signal, sensing and transmitting the output of the actuator in a system to be measured at the first location, converting a physical quantity output from the system to be measured at a second location into an electric signal by a sensor installed at the second location, and measuring a time difference between a change in the driving electric signal and a change in the electric signal from the sensor, comprising: Prior to measuring the time difference, the driving electric signal is controlled so that the actuator alternates between an off state and an on state; a first value of the electrical signal from the sensor before the timing of the actuator changing between an off state and an on state; and acquiring a second value of the electrical signal from the sensor after a predetermined guard time has elapsed after the timing. In measuring the time difference, the delay time is calculated from the difference between the timing of the change in the actuator's drive electric signal and the timing at which the electric signal matches a threshold value based on a first value of the electric signal and a second value of the electric signal.

2. The delay time measurement system according to claim 1, wherein the physical quantity is an image.

3. The delay time measurement system according to claim 1, wherein the physical quantity is sound.

4. The delay time measurement system according to claim 1, wherein the physical quantity is haptics.

5. The delay time measurement system according to claim 1, wherein the physical quantities are at least two of the following: video, sound, and haptics, and what is sensed by the system under test is different from what is output by the system under test.

6. The delay time measurement system according to claim 1, wherein the repetition period when the actuator periodically alternates between the off state and the on state during measurement of the time difference is set to a non-integer multiple of the repetition period of the operation of the system under test.

7. The delay time measurement system according to claim 1, characterized in that when measuring the time difference, the repetition period when the actuator periodically switches between the off state and the on state is determined by random numbers so that it is not a constant value.

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