Microsoft AR/VR patent introduces method for evaluating the alignment of one or more components of a headset

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(XR Navigation Network December 08, 2023）头显一般包括两个分别位于左眼和右眼前面的显示器，而它们之间的不对准可能会以非期望的方式影响显示图像的呈现。

尽管初始校准可以在工厂校准期间和/或通过最终用户执行的校准程序进行设置，但由于外部应变，校准可能会受到损害，例如头显因硬物撞击而导致组件错位。

So in the patent application titled "Alignment assessment for head-mounted display system",MicrosoftA method for evaluating the alignment of one or more components of a headset is presented.

In one embodiment, the headset described in the patent may include one or more strain gauges, each strain gauge having one or more variable strain parameters. Changes in the strain parameters of one or more strain gauges can be detected by the system and used by a logic machine to evaluate the calibration of the headset.

The logic machine may alter one or more aspects of the displayed image based on the evaluated alignment of the display components and/or camera. For example, when it is determined that strain is causing the display assembly to become misaligned relative to the camera, the orientation of the displayed image can be changed accordingly.

Figures 3A and 3B illustrate component misalignment scenarios for a head mounted display system. Specifically, FIG. 3A shows near-eye displays 200L and 200R located in front of the user's eyes 202L and 202R. However, the right near-eye display 200R is misaligned relative to the left near-eye display 200L and relative to the camera 205 .

Specifically, the right near-eye display is offset by about 10 degrees. So in FIG. 3B , the alignment of the right near-eye display 200R is inconsistent with the pose of the head mounted display estimated from the camera captured image, and the display image 204R is not aligned with the display image 204L. In this way, the two displayed images do not resolve to a single three-dimensional object 206, but are viewed as two different offset images. At best, this can be distracting, and at worst, it can cause discomfort and nausea for the user.

Figure 4 illustrates an example head mounted display system 400. Head mounted display system 400 includes a left display assembly 402L, which includes a left light source 404L. Similarly, head-mounted display 400 includes right display component 402R, which in turn includes right light source 404R.

The operation of the display component to provide spatially modulated display light used to form a display image may be controlled by a logic machine, such as logic machine 406 shown in FIG. 4 . For example, a logic engine can control the light source associated with each display component. The logic machine may also or alternatively detect misalignments between various components of the head mounted display system.

Various configurations of the head mounted display system 400 may be used to evaluate the alignment of the head mounted display components. Generally speaking, a head-mounted display may include one or more strain gauges, each strain gauge being based at least in part on the amount of strain applied to the head-mounted display and having one or more variable strain parameters. The invention describes one or more strain gauges in the form of one or more Bragg gratings etched into the optical element.

As another example, the strain gauges may include foil strain gauges. For example, when strain causes the foil pattern to deform, a change in resistance can be detected.

The method 500 shown in FIG. 5 illustrates a method 500 for head-mounted display calibration evaluation in which one or more strain gauges include Bragg gratings formed on an optical element.

At 502, method 500 includes emitting test light from a test light source into an optical element configured to propagate the test light by total internal reflection. The optical element includes one or more Bragg gratings, each grating having a variable light return parameter based at least on an amount of strain applied to the optical element.

In Figure 6, light source 404L is configured to emit display light 602D for forming a display image and test light 602T for evaluating the alignment of the head display 400 components. To this end, the light source includes a first emitter 601D for emitting display light 602D and a second emitter 601T for emitting test light 602T.

Each light emitter is associated with a different light emitting component of the light source. In this case, the characteristics of the test light may differ from the display light in any suitable manner. For example, while display light can generally be spatially modulated to form a display image, test light can include a broad spectrum of wavelengths. For example, the test light may be white light that includes substantially the entire visible light spectrum.

Returning briefly to FIG. 5 , at 504 , method 500 includes detecting test light in an optical element at a test light sensor. Detecting the test light in the optical element may include detecting the wavelength of the test light at the test light sensor.

Optical element 800 shown in Figure 8A may take the form of a waveguide. Optical element 800 is coupled to a test light source 802 configured to emit test light toward the optical element, and to a test light sensor 804 configured to detect the test light from the optical element. Additionally, the optical element between the test light source and the test light sensor forms a Bragg grating 806, which is represented by a plurality of individual grating elements disposed on the sides of the optical element.

In Figure 8A, a test light source emits test light 808, which propagates through optical elements toward a test light sensor 804. The portion of the test light returned by the Bragg grating may represent a relatively narrow wavelength range relative to the test light, for example a wavelength range of a few nanometers, while other wavelengths of the test light continue to propagate through the optical element. Part of the test light returned by the Bragg grating can be detected by the test light sensor, as shown in Figure 8B.

Specifically, FIG. 8B includes a first plot 812 representing the relative intensity of the wavelength spectrum emitted by the test light source 802. This may include "white light". Figure 8B also includes a second graph 814 that represents the relative intensity of various wavelengths of test light detected by the test light sensor 804.

As shown, plot 814 includes a wavelength valley 816, indicating that the range of wavelengths returned by Bragg grating 806 is relatively small. Since the test light sensor is located at the far end of the source end of the test light path, the wavelength returned by the Bragg grating cannot reach the test light sensor, so a wavelength valley 816 is generated in the spectrum of the detection wavelength.

Returning briefly to FIG. 5 , at 506 , method 500 includes evaluating an alignment of one or both of a display component of the head mounted display system and a camera of the head mounted display system based at least in part on the light detected by the test light sensor. Test light. As described above, the logic engine may be configured to evaluate the alignment of one or both of the display assembly and the camera based at least in part on the wavelength of the test light detected by the test light sensor.

For example, Figure 8C shows the optical element 800 of Figure 8A again. In this example, strain 818 is applied to the optical element. Strain can be caused by external forces exerted directly on the optical element.

In any case, the strain exerted on the optical element will affect the element spacing of the grating elements of Bragg grating 806. This affects the wavelength of the test light returned by the Bragg grating. In other words, the variable light return parameter of the Bragg grating results in a strain-dependent return of a first wavelength of test light for a first amount of strain applied to the Bragg grating, and a strain-dependent return of the test light for a second amount of strain applied to the optical element. Strain dependent return at second wavelength.

This can be detected by testing the light sensor, as shown in Figure 8D. Specifically, graph 820 of FIG. 8D shows the relative intensity of wavelengths of test light detected by test light sensor 804 for the scenario shown in FIG. 8C. As mentioned above, the test light sensor 804 is located at the source distal end of the optical path of the test light, so the returned wavelength is represented by the wavelength valley 822 in the detection wavelength spectrum.

Marker 824 represents the location of the detected wavelength valley 816 in the scene shown in Figure 8A, eg, the expected location of the wavelength valley under the strain conditions shown in Figure 8A. In other words, applying strain to the optical element moves the detected wavelength valley from mark 824 to wavelength valley 822 as shown in Figure 8D.

In this way, a logic machine can detect when strain is applied to an optical element by comparing the wavelength of light returned by a Bragg grating at a given moment to the wavelength of light returned by a known Bragg grating at a known strain state.

In other words, when the test light sensor is located at the source far end of the optical path of the test light, the logic machine can detect wavelength valleys relative to the known wavelength spectrum emitted by the test light source, where the wavelength valley is the strain of the test light in the portion of the Bragg grating Related returns are caused. For example, the logic engine may compare the wavelength at which wavelength valley 822 is detected to the wavelength at which wavelength valley 816 is detected.

This can be used to evaluate the alignment of different parts of the headset. For example, previous tests can be used to determine the wavelength of test light returned by different Bragg gratings under different strain conditions.

As one example, this could include examining how the wavelength of the returning light changes as the frame of the headset bends in a way that affects the alignment of the display components by a known amount. So at runtime, the logic machine can evaluate the alignment of the display component by detecting whether the change in the return wavelength of the test light is consistent with the wavelength returned during the test.

For example, previous testing may indicate that the wavelength corresponding to wavelength valley 822 returns when the display assembly is bent about 5 degrees in a known direction relative to the rest of the headset. Thus at run time, when a wavelength valley is detected at the location of valley 822, the logic engine may evaluate the alignment of the display assembly as being 5 degrees off. Wavelength valleys detected at different wavelengths may be consistent with different conditions from previous testing, such as camera misalignment.

It is important to understand that this test can detect virtually any strain condition applied to the headset, especially when multiple Bragg gratings are formed on one or more different optical elements of the headset. During testing, the wavelengths of test light returned by different Bragg gratings can be stored in a lookup table for the headset to query at runtime.

In this way, the logic machine can detect various misalignments of the headset at runtime by querying a lookup table. In other words, after detecting a specific wavelength of the detected test light that corresponds to a specific Bragg grating, the headset can refer to a lookup table to compare the detected wavelength to the known wavelength returned by the Bragg grating to obtain the headset's The strain state is known.

named "Microsoft Patent | Alignment assessment for head-mounted display system"Microsoft patentThe application was originally submitted in April 2022 and was recently published by the US Patent and Trademark Office.