CN109765035B - Mobile delay measurement method of VR helmet based on gradient coding - Google Patents
Mobile delay measurement method of VR helmet based on gradient coding Download PDFInfo
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Abstract
The invention discloses a movement delay measurement method of a VR helmet based on gradual change coding, which adopts a guide rail to drive the VR helmet to move, a light coding plate is formed by splicing a plurality of gray gradual change patterns and codes each pattern; obtaining the light intensity of the gray level gradient pattern through a photosensitive sensor; resolving the position of a pattern boundary in the motion process of the VR helmet; when the VR helmet moves again, inputting corresponding black-and-white images to the VR helmet at the pattern boundary, and sensing the black-and-white images by using a photosensitive sensor; obtaining a square wave curve obtained according to the gray level gradient pattern and a square wave curve output when the photosensitive sensor senses a black-white image, so that the delay time of the VR helmet can be obtained; the method enables the black and white patterns in the VR helmet and the gray scale gradient pattern codes of the VR helmet to be subjected to virtual and real registration, and errors caused by manual waveform alignment in an early method are avoided.
Description
Technical Field
The invention belongs to the technical field of virtual reality equipment, and particularly relates to a movement delay measuring method of a VR helmet based on gradual change coding.
Background
The delay time of a head mounted display device (HMD) is closely related to the user experience, and if the time is slightly longer, it may cause the user to develop "motion sickness" symptoms. The document Luca M d.new Method to Measure End-to-End delay of Virtual Reality [ M ] MIT Press,2010 "proposes a simple scheme of delay measurement, as shown in fig. 1(a), a light-sensitive sensor is fixed on each of the VR helmet shell and the window, a test chart with gradually changed gray scale is displayed on both the display screen and the VR helmet, then the light-sensitive sensor on the shell is tightly attached to the display screen, the VR helmet is tightly attached to the display screen and reciprocates along the direction of the gray scale change, and the waveforms returned by the two sensors are recorded (fig. 1 (b)). The delay time of the VR headset is obtained by calculating the phase difference between the two waveforms. The method has the defects that manual movement is needed, and jitter and the like in the moving process can introduce a lot of noise to the signal processing at the rear part; the method for manually aligning the frequency domain waveform solves the problem of errors caused by asynchronism between the pattern in the virtual space and the pattern in the display screen, and for the tiny time of delay time, the method sometimes cannot eliminate the errors but introduces new errors; the test method has a VR headset for the headset, which needs to be able to calculate its own position data with so much shadowing that is not friendly to the tracking scheme of many VR headsets; the resulting data has large variance and its instability dictates that it cannot be used to make a measurement instrument.
Disclosure of Invention
In view of the above, an object of the present invention is to provide a movement delay measurement method for a VR headset based on gradient coding, which can accurately measure a time delay of the VR headset during movement by a simple device.
A moving delay measurement method of a VR helmet based on gradual change coding uses a measurement device which comprises a first photosensitive sensor (1), a VR helmet (2), an object stage (3), a numerical control guide rail (4), a guide rail controller (5), a light coding plate (6) and a second photosensitive sensor (7); a light coding plate (6) is arranged on one side of the numerical control guide rail (4); an object stage (3) of the numerical control guide rail (4) can move linearly along a rail under the control of a guide rail controller (5), a first photosensitive sensor (1) and a VR helmet (2) are fixed on the object stage (3), wherein the first photosensitive sensor (1) can sense patterns on a light coding plate (6) in the process of following the object stage (3) to move, and a second photosensitive sensor (7) is fixed on a display window of the VR helmet (2);
the optical coding plate (6) is formed by splicing a plurality of gray level gradient patterns along the travel direction of the guide rail (4), one end of each gray level gradient pattern is black, the other end of each gray level gradient pattern is white, and the middle gray level is continuously and gradually changed; two adjacent gray gradation patterns are symmetrical with respect to the boundary;
the mobile delay measuring method comprises the following specific steps:
and 5, according to the position data set recorded before, combining the current position of the VR helmet (2) to calculate, and the VR helmet (2) displays a corresponding black-and-white picture, namely: outputting a black pattern to the VR helmet (2) when the calculated position is a white to black position; outputting a white pattern to the VR helmet (2) when the calculated position is a black-to-white position; the second photosensitive sensor (7) senses a black-white image output by the lens of the VR helmet (2) in the process, when the white image is sensed, the second photosensitive sensor (7) returns to a high level, and when the black image is sensed, the second photosensitive sensor (7) returns to a low level, so that a square wave signal is obtained and serves as a detection waveform;
and 7, calculating the time delay delta t of the measured waveform relative to the reference waveform, thereby obtaining the time delay of the VR helmet (2).
Further, in step 7, a reference waveform and a detected waveform are subjected to linear fitting, and then sampling is performed to obtain more data volumes, and the specific method includes:
A. numbering boundaries of the gray level gradient patterns on the optical coding plate (6) from left to right in sequence, and correspondingly numbering reference waveforms obtained based on the optical coding plate (6) and jump edges of detection waveforms corresponding to the reference waveforms;
B. establishing a coordinate system by taking time as an x axis and numbering as a y axis, taking time information of a jumping edge of the reference waveform square wave as an x coordinate, and taking a number value of the jumping edge as a y coordinate, and drawing discrete points representing the number and the time of the jumping edge in the coordinate system; similarly, obtaining discrete points corresponding to each jumping edge of the detected waveform;
C. respectively carrying out linear fitting on the two groups of discrete points to obtain two curves, and sampling the y value by setting step length to obtain a coordinate difference value of an x axis between the two curves under the same y value, namely delay time data of a detection waveform relative to a reference waveform; and after the y-axis effective interval is sampled for a plurality of times, obtaining a plurality of delay time data and calculating the average value, thus obtaining the accurate time delay of the VR helmet (2).
Further, the object stage (3) is controlled to move repeatedly on the guide rail (4) to obtain a plurality of reference waveforms and detection waveform curves, so that a plurality of delays delta t are obtained, and after averaging, the average value is used as the accurate time delay of the VR helmet (2).
Furthermore, the number of the gray-scale gradient patterns on the optical coding plate (6) is odd.
The invention has the following beneficial effects:
the invention discloses a movement delay measurement method of a VR helmet based on gradual change coding, which adopts a guide rail to drive the VR helmet to move, a light coding plate is arranged on one side of the guide rail, the light coding plate is formed by splicing a plurality of gray gradual change patterns, and each pattern is coded; obtaining the light intensity of the gray level gradient pattern through a photosensitive sensor; resolving the position of a pattern boundary in the motion process of the VR helmet; when the VR helmet moves again, inputting corresponding black-and-white images to the VR helmet at the pattern boundary, and sensing the black-and-white images by using a photosensitive sensor; obtaining a square wave curve obtained according to the gray level gradient pattern and a square wave curve output when the photosensitive sensor senses a black-white image, so that the delay time of the VR helmet can be obtained; the method enables the black and white pattern in the VR helmet and the gray scale gradient pattern code of the VR helmet to be subjected to virtual and real registration, and errors caused by manual waveform alignment in an early method are avoided; by means of round-trip multiple measurement and linear fitting, test data samples are greatly increased, and the expectation of the data is closer to the real delay time.
Drawings
Fig. 1(a) is a diagram of a conventional experimental apparatus for measuring VR headset movement delay;
FIG. 1(b) is a graph of experimental signals obtained based on the experimental set-up of FIG. 1 (a);
FIG. 2 is a schematic view of a measuring device according to the present invention;
fig. 3(a) is a schematic view of the installation of a VR headset and a photosensor in the present invention;
FIG. 3(b) is a schematic diagram of a light-encoding plate employed in the present invention;
FIG. 4(a) is a diagram of a detection waveform signal fed back by the second photosensor; fig. 4(b) is a sine wave signal fed back by the first photosensitive sensor, and fig. 4(c) is a square wave signal converted from the sine wave signal, i.e. a reference waveform diagram;
FIG. 5 is a detected waveform and a reference waveform obtained for a single motion;
FIG. 6 is a waveform fit to FIG. 5;
FIG. 7 is a detected waveform and a reference waveform obtained during multiple round trips;
FIG. 8 is a waveform fit to FIG. 7;
the system comprises a first photosensitive sensor 1, a 2-VR helmet, a 3-objective table, a 4-numerical control guide rail, a 5-guide rail controller, a 6-optical coding plate and a 7-second photosensitive sensor.
Detailed Description
The invention is described in detail below by way of example with reference to the accompanying drawings.
The invention discloses a movement delay measuring method of a VR helmet based on gradual change coding, and a measuring device used in the method is shown in figure 2 and comprises a first photosensitive sensor 1, a VR helmet 2, an object stage 3, a high-precision numerical control guide rail 4, a guide rail controller 5, a light coding plate 6 and a second photosensitive sensor 7. A light coding plate 6 is arranged on one side of the numerical control guide rail 4; the object stage 3 of the numerical control guide 4 can move linearly along the track under the control of the guide controller 5, the first photosensitive sensor 1 and the VR helmet 2 are fixed on the object stage 3, wherein the first photosensitive sensor 1 can sense the pattern on the optical coding plate 6 during the process of following the object stage 3, and the second photosensitive sensor 7 is fixed on the display window of the VR helmet 2, as shown in fig. 3 (a).
As shown in fig. 3(b), the optical encoding plate 6 is formed by splicing a plurality of gray-scale gradient patterns along the travel direction of the guide rail 4, one end of each gray-scale gradient pattern is black, the other end is white, and the intermediate gray scale is continuously and gradually changed; two adjacent gray gradation patterns are symmetrical with respect to the boundary line.
The mobile delay measuring method comprises the following specific steps:
1. firstly, controlling the objective table 3 to move at a constant speed along the numerical control guide rail 4 from an initial position, wherein no image is input into the VR helmet 2, but the position of the VR helmet is calculated at any moment;
2. in the moving process of the object stage 3, the first photosensitive sensor 1 senses the gray-scale gradient pattern on the coding plate 6 and generates a voltage analog signal according to the gray-scale value of the pattern; at the moment of sensing the maximum value and the minimum value of the signal, the VR helmet 2 calculates the position of the helmet at each moment and records the position; the positions comprise two types, the maximum value moment corresponds to a black-to-white position, and the minimum value moment corresponds to a white-to-black position.
3. After the whole movement is completed, a group of position data sets of the VR helmet 2 is obtained;
4. then the object stage 3 is controlled to move from the initial position again, and the data returned by the first photosensitive sensor 1 and the second photosensitive sensor 7 are recorded simultaneously in the moving process;
5. according to the position data set recorded before, combining with the current position information of the VR headset 2, the VR headset 2 displays the corresponding black and white picture, that is: when the calculated position is a black-to-white position, outputting a white pattern to the VR helmet 2; outputting a black pattern to the VR helmet 2 when the calculated position is a white to black position; the second photosensor 7 thereon senses a black-and-white image output from the lens of the VR headset 2 in this process, and when a white image is sensed, the second photosensor 7 returns to a high level, and when a black image is sensed, the second photosensor 7 returns to a low level, thereby obtaining a square wave signal as a detection waveform, as shown in fig. 4 (a).
6. Meanwhile, the first photosensor 1 senses the gray-scale gradation pattern on the optical encoder plate 6, and generates a voltage analog signal according to the gray-scale value of the pattern, thereby obtaining a sine wave signal, as shown in fig. 4(b), and then converts it into a square wave signal, as a reference waveform, as shown in fig. 4 (c);
7. data processing: since the VR headset 2 has a time delay in resolving its position, when the stage 3 moves to a certain position, the VR headset 2 cannot immediately sense the position, and there is a time delay, and therefore, as shown in fig. 5, the detected waveform has a time delay Δ t with respect to the reference waveform; therefore, calculating the time delay Δ t yields the time delay for the VR headset 2. By averaging the multiple time delays at on the detected waveform and the reference waveform, a more accurate time delay for the VR headset 2 can be obtained.
In order to increase the data volume of multiple averaging, in the invention, a reference waveform and a detection waveform are subjected to linear fitting, and then sampling is carried out to obtain more data volume, and the specific method comprises the following steps:
A. the boundary lines of the gray level gradient patterns on the optical coding plate 6 are sequentially assigned with numbers from left to right, namely, the boundary line No. 1, the boundary line No. 2 and the like; the reference waveform obtained based on the optical code plate 6 and the respective transition edges (rising edge and falling edge) of the detected waveform corresponding to the reference waveform are also numbered correspondingly.
B. Establishing a coordinate system by taking time as an x axis and numbering as a y axis, taking time information of a jumping edge of the reference waveform square wave as an x coordinate, and taking a number value of the jumping edge as a y coordinate, and drawing discrete points representing the number and the time of the jumping edge in the coordinate system; and similarly, obtaining discrete points corresponding to each jumping edge of the detected waveform.
C. Respectively carrying out linear fitting on the two groups of discrete points to obtain two curves, and sampling the y value by setting step length to obtain a coordinate difference value of an x axis between the two curves under the same y value, namely delay time data of a detection waveform relative to a reference waveform; and after the y-axis effective interval is sampled for multiple times, a large amount of delay time data is obtained, and the average value is obtained, so that more accurate time delay can be obtained.
To further increase the data volume, the VR headset 2 should be moved back and forth on the guide rail 4 multiple times to obtain more detected waveforms and reference waveforms; however, the moving direction of the object stage 3 needs to be determined during the reciprocating movement, in order to automatically distinguish the moving direction, the optical coding plate 6 with the direction is adopted in the invention, the number of the gray-scale gradient patterns is odd, the gray value of the starting point of the first gray-scale gradient pattern on the optical coding plate 6 is just opposite to the gray value of the end point of the last gray-scale gradient pattern on the optical coding plate 6, and the signals correspondingly fed back by the first photosensitive sensor 1 are the minimum value and the maximum value; when the object stage 3 moves to the end point of the last gray scale gradient pattern and needs to turn back, the maximum value signal fed back by the first photosensitive sensor 1 will continue for a period of time due to the reaction delay of the guide rail 4, as shown in fig. 7, so the peak signal here is obviously different from the middle peak signal, which indicates that the object stage 3 has moved to the end point position; when the object table 3 returns to the starting point of the travel of the guide rail 4, the gray gradient pattern is black, and the same as the end point, the minimum value signal fed back by the first photosensitive sensor 1 continues for a period of time when the object table returns, which indicates that the object table 3 has returned to the starting point position, so that the moving direction can be distinguished.
After the reciprocating movement is performed for a plurality of times, the directionality of the signal of the optical encoding plate 6 is used to determine whether the movement is forward or backward, the slope of the fitting curve is positive when the movement is forward, and the slope of the fitting curve is negative when the movement is backward, so that the waveform shown in fig. 8 is obtained. At this point, all time delays Δ T in the effective area (1-8) are calculated in groups, and the average value is the delay time T of the equipment.
In summary, the above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (4)
1. A movement delay measurement method of a VR helmet based on gradual change coding is characterized in that a measurement device used in the method comprises a first photosensitive sensor (1), the VR helmet (2), an object stage (3), a numerical control guide rail (4), a guide rail controller (5), a light coding plate (6) and a second photosensitive sensor (7); a light coding plate (6) is arranged on one side of the numerical control guide rail (4); an object stage (3) of the numerical control guide rail (4) can move linearly along a rail under the control of a guide rail controller (5), a first photosensitive sensor (1) and a VR helmet (2) are fixed on the object stage (3), wherein the first photosensitive sensor (1) can sense patterns on a light coding plate (6) in the process of following the object stage (3) to move, and a second photosensitive sensor (7) is fixed on a display window of the VR helmet (2);
the optical coding plate (6) is formed by splicing a plurality of gray level gradient patterns along the stroke direction of the numerical control guide rail (4), one end of each gray level gradient pattern is black, the other end of each gray level gradient pattern is white, and the middle gray level is continuously and gradually changed; two adjacent gray gradation patterns are symmetrical with respect to the boundary;
the mobile delay measuring method comprises the following specific steps:
step 1, firstly, controlling an objective table (3) to move at a constant speed along a numerical control guide rail (4) from an initial position, and constantly calculating the position of a VR helmet (2);
step 2, in the moving process of the objective table (3), the first photosensitive sensor (1) senses a gray gradient pattern on the optical coding plate (6) and generates an analog voltage signal according to the gray value of the pattern; at the moment of sensing the maximum value and the minimum value of the voltage signal, the VR helmet (2) calculates the position of the helmet at each moment and records the position; the positions comprise two types, the maximum value moment corresponds to a black-to-white position, and the minimum value moment corresponds to a white-to-black position;
step 3, obtaining a group of position data sets of the VR helmet (2) after the whole movement is finished;
step 4, controlling the object stage (3) to move from the initial position again, calculating the position of the object stage at any moment in the VR helmet (2) in the movement process, and simultaneously recording data returned by the first photosensitive sensor (1) and the second photosensitive sensor (7);
and 5, according to the position data set recorded before, combining the current position of the VR helmet (2) to calculate, and the VR helmet (2) displays a corresponding black-and-white picture, namely: outputting a black pattern to the VR helmet (2) when the calculated position is a white to black position; outputting a white pattern to the VR helmet (2) when the calculated position is a black-to-white position; the second photosensitive sensor (7) senses the black and white image output by the display window of the VR helmet (2) in the process, when the white image is sensed, the second photosensitive sensor (7) returns to a high level, and when the black image is sensed, the second photosensitive sensor (7) returns to a low level, so that a square wave signal is obtained and serves as a detection waveform;
step 6, at the same time, the first photosensitive sensor (1) senses the gray gradient pattern on the optical coding plate (6), and generates a voltage analog signal according to the gray value of the pattern, thereby obtaining a sine wave signal; then converting the signal into a square wave signal as a reference waveform;
and 7, calculating the time delay delta t of the measured waveform relative to the reference waveform, thereby obtaining the time delay of the VR helmet (2).
2. The method for measuring the movement delay of the VR headset based on the gradual change coding as claimed in claim 1, wherein in step 7, the reference waveform and the detected waveform are linearly fitted and then sampled to obtain more data volume, and the method comprises:
A. numbering boundaries of the gray level gradient patterns on the optical coding plate (6) from left to right in sequence, and correspondingly numbering reference waveforms obtained based on the optical coding plate (6) and jump edges of detection waveforms corresponding to the reference waveforms;
B. establishing a coordinate system by taking time as an x axis and numbering as a y axis, taking time information of a jumping edge of a reference waveform square wave as an x coordinate, and taking a number value of the jumping edge of the reference waveform square wave as a y coordinate, and drawing discrete points representing the number and the time of the jumping edge in the coordinate system; similarly, obtaining discrete points corresponding to each jumping edge of the detected waveform;
C. respectively carrying out linear fitting on the two groups of discrete points to obtain two curves, and sampling the y value by setting step length to obtain a coordinate difference value of an x axis between the two curves under the same y value, namely delay time data of a detection waveform relative to a reference waveform; and after the y-axis effective interval is sampled for a plurality of times, obtaining a plurality of delay time data and calculating the average value, thus obtaining the accurate time delay of the VR helmet (2).
3. The method for measuring the movement delay of a VR helmet based on gradual change coding as claimed in claim 1 or 2, wherein the control stage (3) is moved repeatedly on the numerical control guide (4) to obtain a plurality of reference waveforms and detection waveform curves, thereby obtaining a plurality of delays Δ t, and after averaging, the average is used as the accurate time delay of the VR helmet (2).
4. The method of claim 3, wherein the number of grayscale gradation patterns is an odd number.
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