As an important evaluation specification of the helmet mounted display, binocular alignment directly affects the imaging quality of the helmet mounted display, such as the imaging distance and the imaging clarity, and then has a vital impact on the combat effectiveness of the pilot and the aircraft. The traditional detection method relies on the human eye to align the collimator for subjective interpretation, the results are often uncertain because different people have different feelings. This paper proposes an automatic measurement method of binocular alignment based on a single digital camera. This method combines the binocular images of the helmet mounted display into the same optical path by placing a turning prism at the binocular exit pupil position of the helmet mounted display, thereby achieving the purpose of synchronously collecting binocular images by using a single digital camera. Digital image processing technology realizes automatic calculation of binocular alignment indicators, which greatly improves the measurement accuracy and the measurement efficiency. This method uses a turning prism to merge the binocular images of the helmet mounted display into one optical path. The camera can collect binocular images without moving during the measurement process, so it can avoid the straightness error caused by the use of a translation stage, and finally an objective, accurate and fast measurement of binocular alignment specification is obtained. At last, this article discusses the measurement principle of the method in detail, explains the optical-mechanical structure of the binocular alignment measurement equipment in detail, and analyzes the measurement accuracy. Finally, several binocular alignment test results are compared. The test results show that this method has obvious advantages in the measurement accuracy and the measurement efficiency. It can meet the needs of fast, accurate and objective measurement of the binocular alignment of the helmet mounted display, and has the value of a wide range of applications.
The minimum resolution is one of the most important characteristics of human vision, during the flight of the aircraft, the pilot uses the head-up display(HUD) to observe and distinguish the information of the external scenery. Analyzing the impact of different transmittance HUD combiner under different environment brightness on the external resolution has important instruction and application value for aviation safety. The experiment uses the UASF1951 target plate and the transmittance of HUD combiners under two different environmental brightness. Record the minimum resolution angle and the difference between the two conditions. The result shows that, under the same brightness, the lower the contrast, the weaker the human eye can recognize; the minimum resolvability of the human eye is affected by contrast: when the brightness is lower, the lower the brightness, the higher the minimum contrast requirement for human eye to recognize objects. When the brightness is higher, the minimum contrast requirement for human eye to recognize objects does not change much with brightness, and after the brightness is increased to a certain range, the minimum contrast required by the human eye to recognize the object is almost unchanged. It can be seen that the resolution of the human eye is simultaneously affected by environmental brightness and contrast, and the experimental results basically conform to the Adrian’s Visual Acuity Model.
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