Facebook Patent | Viewing optics test subsystem for head mounted displays

Patent: Viewing optics test subsystem for head mounted displays

Publication Number: 10198978

Publication Date: 2019-02-05

Applicants: Facebook

Abstract:

An optical evaluation workstation evaluates quality metrics (e.g., optical contrast) of optical elements of a HMD. The workstation includes a test pattern, an optical element feed assembly, a light source, a camera and a control module. The light source backlights the test pattern with diffuse light. The optical element feed assembly receives an optical element of a HMD and places the optical element at a first distance from the test pattern corresponding to a distance between the optics block in the HMD and an exit pupil of the HMD. The camera images the test pattern through the optical element and the camera is positioned at a second distance from the test pattern corresponding to a distance between the exit pupil and an electronic display in the HMD. The control module generates a test report for presentation to a user based on the evaluation of the optical element.

Background:

The disclosure relates generally to testing optical components, and specifically to systems for performing quality assurance tests on optics for head-mounted displays (HMDs).

In the context of an HMD, optical contrast (or contrast) indicates how well a HMD separates brightness and darkness in images presented to a user of the HMD. However, in this context, contrast is affected by different components of the HMD (e.g., display, optics, etc.) and it is difficult to quantitatively determine how each of the individual components of an HMD affects contrast. Additionally, while standardized test patterns (e.g., American National Standards Institute (ANSI) contrast pattern) exist that facilitate measurement of contrast, there is no standardized tests or systems to measure contrast, let alone in the context of HMDs.

Summary:

An optical evaluation workstation is designed to simulate the exact environment of a HMD to test the optical qualities of its viewing optics.

The optical evaluation workstation includes an optical test assembly and a control module. The optical test assembly further includes a light source, an optical element feed assembly, a test pattern assembly and a camera. The optical element feed assembly is configured to receive one or more viewing optics for testing. The test pattern assembly receives a test pattern which represents an electronic display element in a HMD and in the test pattern assembly it is backlight with diffuse light emitting from the light source. The one or more viewing optics are positioned between the test pattern assembly and the camera. The camera is placed at a distance from the test pattern that is representative of a distance between an eye of a user of the HMD and the electronic display element. The camera then takes images of the test pattern through the one or more viewing optics with and without the diffuse light applied to the test pattern.

The control module enables the optical evaluation workstation to operate a series of test procedures, executing an optical quality test to evaluate the one or more viewing optics in view of one or more quality metrics. An optical quality metric is an optical characteristic that indicates how well an optical element meets certain optical performance requirements. For example, one quality metric is optical contrast. The one or more viewing optics are first loaded into the optical element feed assembly in the optical test assembly. After the one or more viewing optics are adjusted in a proper position inside the optical element feed assembly, a background image of the test pattern is taken by the camera with the light source turned off, indicating that no light is applied to the test pattern. This image represents a dark frame, which ideally should be completely black. The light source is then turned on and provides diffuse light to the test pattern. The viewing camera then takes a series of images of the test pattern through the one or more testing optics while the test pattern is backlit with the diffuse light. A final image is generated to average noise based on the multiple images taken by the camera when light is applied. Finally, the background image is subtracted from the final image and a test report is generated for the one or more viewing optics being evaluated. The test report determines with some reference whether the one or more viewing optics meet the quality metrics. For example, the one or more viewing optics failing an optical contrast test may indicate that the one or more viewing optics are defective and should be discarded.

Some adjustment methods are also applied in the optical evaluation workstation to generate effective performances. The position of the test pattern assembly is calibrated to be vertically centered consistent with the testing viewing optics and with the camera. The physical distances between different components in the optical test assembly can also be adjusted conveniently and accurately to simulate the exact environment inside a HMD. In some embodiments, these physical distances are strictly controlled to simulate the amount of light that can go into a user’s eye to correlate well to human’s visual performance.