Fire helmet optical display system design method based on freeform prism

Abstract

The application discloses a design method of a fire helmet optical display system based on a free-form surface prism, belongs to the technical field of AR, and solves the technical problems that, in the prior art, the influence of high temperature, thermal radiation and air thermal halo effect on imaging quality is not considered, and the influence of thermal deformation of a fire mask under high temperature on imaging quality, leading to the fact that, during fire fighting, imaging quality is seriously deteriorated, image contrast and signal-to-noise ratio are significantly reduced, and clear, stable and reliable information cannot be provided under a high-temperature fire scene. Through thermal analysis on the mask, the mask is fitted as a free-form surface and is brought into optical design software for integrated design, light beams emitted by a micro display pass through a double-cemented lens, a transmission surface, a total reflection surface, a half-reflection half-transmission surface and a total reflection surface, and are refracted into human eyes, and light beams of a real scene pass through the mask, are refracted through a refractive surface, a half-reflection half-transmission surface and a total reflection surface, and are refracted into human eyes. The application is used for realizing a fire helmet optical display system capable of providing clear, stable and reliable information.

Description

Technical Field

[0001] This invention relates to the field of AR technology, specifically to a design method for an optical display system for fire helmets based on freeform prisms. Background Technology

[0002] Augmented Reality (AR) technology significantly expands human perception and decision-making capabilities in complex environments by overlaying and fusing computer-generated virtual information (such as navigation markers, structural perspectives, hazard identification, and vital sign indicators) into the user's real-world field of view in real time. In critical firefighting missions such as earthquake relief, AR systems integrated into helmet-mounted displays (HMDs) provide firefighters with crucial situational awareness enhancements when venturing into rubble for search and rescue operations. This includes seeing through obstructions, identifying survivor locations, providing structural risk warnings, and optimizing rescue routes, thereby significantly improving search and rescue efficiency and personnel survival rates.

[0003] Firefighting environments (especially fire scenes and potentially high-temperature areas after earthquakes) experience extreme heat loads. The resulting high temperatures cause geometric deformation and refractive index temperature drift (dn / dT effect) in core AR optical system components (such as prisms and lenses), disrupting precise optical path design and leading to severe image quality degradation. This manifests as defocusing, astigmatism, field curvature, increased chromatic aberration, and virtual-to-real-time registration errors. Simultaneously, the transparent face shield of fire helmets undergoes thermal deformation at high temperatures, altering its surface shape and optical properties, further exacerbating image degradation. Environmental thermal radiation (thermal noise) and atmospheric corona effects also significantly reduce image contrast and signal-to-noise ratio. These thermally induced aberrations and noise issues, particularly the additional aberrations caused by the thermal deformation of fire helmet face shields, severely restrict the AR system's ability to provide clear, stable, and reliable information in high-temperature firefighting scenarios, directly threatening rescue effectiveness and personnel safety.

[0004] In the prior art, Chinese patent document CN208384244U discloses "An optical system and display device based on a freeform prism". The optical system based on a freeform prism includes a backlight module, a beam splitting unit, a silicon-based liquid crystal display, and a freeform prism arranged sequentially along the optical path. The backlight module is used to generate light. The beam splitting unit reflects light with a first polarization state and transmits light with a second polarization state. The silicon-based liquid crystal display is used to reflect light and change the polarization state of the light. The light generated by the backlight module propagates to the beam splitting unit. The beam splitting unit reflects the light with the first polarization state to the silicon-based liquid crystal display. The silicon-based liquid crystal display changes the polarization state of the light and reflects the light back to the beam splitting unit. The beam splitting unit transmits the light from the silicon-based liquid crystal display to the freeform prism. The light exits after passing through the freeform prism. The virtual image generated by the silicon-based liquid crystal display has high brightness, providing users with a good user experience. However, this technical solution does not consider the impact of high temperature, thermal radiation and air coma on image quality, nor does it consider the thermal deformation of the fire hood in high temperature environment and its impact on image quality. Direct application in fire fighting environment will lead to serious degradation of image quality. The deformation of the fire hood introduces additional aberrations and reduces image contrast and signal-to-noise ratio, making it unable to provide clear, stable and reliable information in high temperature fire fighting scenarios.

[0005] In summary, existing technologies fail to consider the impact of high temperature, thermal radiation, and air coma on image quality, as well as the impact of thermal deformation of fire-fighting masks at high temperatures on image quality. This results in severe degradation of image quality, a significant reduction in image contrast and signal-to-noise ratio during firefighting operations, and an inability to provide clear, stable, and reliable information in high-temperature firefighting scenarios. Summary of the Invention

[0006] This invention solves the technical problem that existing technologies fail to consider the impact of high temperature, thermal radiation, and air thermal corona effects on image quality, as well as the impact of thermal deformation of fire-fighting masks at high temperatures on image quality. As a result, the image quality is severely degraded during fire-fighting operations, and the image contrast and signal-to-noise ratio are significantly reduced, making it impossible to provide clear, stable, and reliable information in high-temperature fire-fighting scenarios.

[0007] The fire helmet optical display system based on a freeform prism of the present invention includes a microdisplay, a doublet lens, a freeform prism, a fire helmet and an auxiliary prism. The freeform prism includes a total reflection surface S1, a total reflection surface S1', a semi-reflective surface S2 and a transmissive surface S3. The auxiliary prism includes a refractive surface S4.

[0008] The microdisplay emits a light beam, which is refracted to the transmission surface S3 by a double cemented lens. The light beam is then transmitted from the transmission surface S3 to the total reflection surface S1'. The total reflection surface S1' reflects the light beam to the semi-reflective and semi-transparent surface S2. The light beam is then reflected by the semi-reflective and semi-transparent surface S2 to the total reflection surface S1. Finally, the light beam is refracted by the total reflection surface S1 and enters the human eye.

[0009] The beam of light from the real scene passes through the fire hood, and is refracted by the refraction surface S4 to the semi-reflective surface S2. It then passes through the semi-reflective surface S2 and the total reflection surface S1 in sequence before entering the human eye.

[0010] Furthermore, in one embodiment of the present invention, the doublet lens is formed by bonding a biconvex lens and a biconcave lens together, including an exit surface S5, a bonding surface S6 and an incident surface S7, wherein the biconcave lens is made of EP9000 material and the biconvex lens is made of APL5514ML material.

[0011] The light beam emitted by the microdisplay enters the cemented doublet through the incident surface S7 of the biconvex lens, and after being refracted by the cemented surface S6, it exits from the exit surface S5.

[0012] Furthermore, in one embodiment of the present invention, the distance between the center of the incident surface S7 and the exit surface S5 is less than or equal to 6 mm, and the center thickness of both the biconvex lens and the biconcave lens is not less than 1.2 mm.

[0013] Furthermore, in one embodiment of the present invention, the freeform prism and the auxiliary prism are both made of COC material, and the fire-fighting mask is made of PC material.

[0014] Furthermore, in one embodiment of the present invention, the total reflection surface S1, the total reflection surface S1', the semi-reflective and semi-transparent surface S2, and the refractive surface S4 are freeform surfaces, the transmission surface S3 and the exit surface S5 are even-order aspherical surfaces, and the cemented surface S6 and the incident surface S7 are standard surfaces.

[0015] Furthermore, in one embodiment of the present invention, the total reflection surface S1 is offset from the optical axis by -1.162 mm in the y direction and tilted counterclockwise by 1.63° around the x-axis;

[0016] The semi-reflective and semi-transparent surface S2 is offset from the optical axis by -1.58mm in the y direction and rotates 24.3° clockwise around the x-axis;

[0017] The transmission surface S3 is offset from the optical axis by 17.49 mm in the y direction and rotates counterclockwise by 50.2° around the x-axis;

[0018] The refracting surface S4 is offset from the optical axis by 0.08 mm in the y direction and rotates counterclockwise by 0.625° around the x-axis;

[0019] The emission surface S5 is offset from the optical axis by 19.932 mm in the y direction and rotates counterclockwise by 51.566° around the x-axis.

[0020] Furthermore, in one embodiment of the present invention, the distance between the total reflection surface S1 and the human eye is less than or equal to 20 mm, the distance between the refractive surface S4 and the fire-fighting mask is less than or equal to 18 mm, and the thickness of the fire-fighting mask is less than or equal to 3 mm.

[0021] The present invention describes a design method for an optical display system for a fire helmet based on a freeform prism. The method, used to construct any of the aforementioned systems, includes the following steps:

[0022] Step 1: Construct a freeform prism module, including a microdisplay, a cemented doublet lens, a freeform prism, and an auxiliary prism. Construct a three-dimensional optical model of the fire hood and fit it to a freeform surface.

[0023] Step 2: Taking the freeform prism module and the fire hood as a whole, optimize the design of the freeform prism module to obtain the optimized freeform prism module.

[0024] Step 3: Perform finite element analysis on the freeform surface fitted by the fire helmet described in Step 1. Based on the finite element analysis results, perform a heatless design on the optimized freeform surface prism module to obtain the final fire helmet optical display system.

[0025] Furthermore, in one embodiment of the present invention, in the freeform surface term fitted by the mask, Y1=0.065, X2=-0.011, Y2=-0.0044, X2Y1=7.59E-006, and Y3=2.61E-006.

[0026] Furthermore, in one embodiment of the present invention, the optimization design of the freeform prism module and the thermal-free design of the optimized freeform prism module both employ a reverse design method. The positive and negative edge field-of-view principal rays are incident on the freeform prism module from the exit pupil position, and the interference between the positive and negative edge field-of-view principal rays is controlled to prevent interference on any surface. Specifically:

[0027] ;

[0028] ;

[0029] Among them, Y B Let Y be the coordinate of point B in the Y direction. C Let C be the coordinates of point C in the Y direction, and Z be the coordinates of point C in the Z direction. B Let B be the coordinate of point B in the Z direction, Z C Let C be the coordinates of point C in the Z direction;

[0030] ;

[0031] ;

[0032] Among them, Y D Let D be the coordinate of point D in the Y direction, Y E Let E be the coordinate of point E in the Y direction, Z... D Let D be the coordinates of point D in the Z direction, Z E Let E be the coordinate of point E in the Z direction;

[0033] ;

[0034] ;

[0035] Among them, Y I Let I be the coordinate of point I in the Y direction, Y E Let E be the coordinate of point E in the Y direction, Z... I Let I be the coordinate of point I in the Z direction, Z D Let D be the coordinates of point D in the Z direction;

[0036] ;

[0037] ;

[0038] ;

[0039] Among them, Y F Let F be the coordinate of point F in the Y direction, Y G Let G be the coordinates of point G in the Y direction, Z... F Let F be the coordinate of point F in the Z direction, Z G Let G be the coordinates of point G in the Z direction, Y... H Let H be the coordinates of point H in the Y direction, Y G Let G be the coordinates of point G in the Y direction.

[0040] This invention solves the technical problem that existing technologies, due to their failure to consider the impact of high temperature, thermal radiation, and air corona effects on image quality, as well as the impact of thermal deformation of fire-fighting masks at high temperatures on image quality, result in severely degraded image quality, significantly reduced image contrast and signal-to-noise ratio during firefighting operations, and an inability to provide clear, stable, and reliable information in high-temperature firefighting scenarios. Specific beneficial effects include:

[0041] 1. This invention proposes a design method for an optical display system for fire helmets based on freeform prisms. Based on an in-depth thermal-structural-optical coupling analysis of the AR optical system applied to fire helmets, its performance stability under expected thermal environments is accurately evaluated. By adopting heat-resistant materials, optimizing the thermal management layout, and minimizing heat-sensitive elements, an optical architecture with excellent thermal stability is designed to suppress thermal deformation and refractive index drift, avoid the impact of high temperature, thermal radiation, and air coma on image quality, and ensure that high image quality is maintained over a wide temperature range, with key indicators such as MTF, distortion, and chromatic aberration meeting the standards.

[0042] 2. This invention proposes a design method for an optical display system for fire helmets based on freeform prisms. Through the integrated design of "display-mask", the fire helmet mask is regarded as an important component of the optical system. The performance stability of the fire helmet mask under the expected thermal environment is accurately evaluated. Based on the heated fire helmet mask model, the freeform prism module is optimized to achieve a heatless design and avoid thermal deformation of the fire helmet mask under high temperature and its impact on imaging quality. Attached Figure Description

[0043] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0044] Figure 1 This is a schematic diagram of the optical display system for the fire helmet described in Embodiment 1;

[0045] Figure 2 This is a schematic diagram of the freeform prism projection channel as described in Embodiment 1;

[0046] Figure 3 This is a schematic diagram of the transmission channel of the freeform prism described in Embodiment 1;

[0047] Figure 4 It is the MTF of each field of view at the Nyquist frequency as described in Implementation Method 1;

[0048] Figure 5 This is a schematic diagram of the field curvature and distortion of the transmitted light path with the fire-fighting mask after thermal analysis as described in Embodiment 1.

[0049] Figure 6 This is a schematic diagram of the overall optical path with a fire-fighting mask as described in Embodiment 1;

[0050] Figure 7 This is the Ansys analysis diagram of the thermal volume change of the fire-fighting mask as described in Implementation Method 1;

[0051] Figure 8 It refers to the thermal deformation and fitting residual of the fire-fighting mask after heating, as described in Embodiment 1;

[0052] Figure 9 This is a schematic diagram showing the changes in MTF values ​​at the Nyquist frequency of the center field of view, 0.7 field of view, and edge field of view of the projection optical path before thermal analysis as described in Embodiment 1, as a function of temperature.

[0053] Figure 10 This is a schematic diagram of the MTF of the projection optical path at an ambient temperature of 60°C after thermal analysis as described in Embodiment 1.

[0054] Figure 11 This is a schematic diagram of the transmission optical path MTF with a fire-fighting mask before thermal analysis as described in Embodiment 1;

[0055] Figure 12 This is a schematic diagram of the MTF transmission optical path with fire-fighting mask after thermal analysis as described in Embodiment 1;

[0056] Figure 13 This is a schematic diagram of the vertical axis color difference as described in Embodiment 1;

[0057] Figure 14 This is a schematic diagram of the optimized projection channel mesh distortion as described in Implementation Method 1;

[0058] Figure 15 It is the optimized projection channel point map described in Implementation Method 1. Detailed Implementation

[0059] Various embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings. The embodiments described with reference to the drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0060] Implementation Method 1

[0061] The fire helmet optical display system based on freeform prism includes a microdisplay, a doublet lens, a freeform prism, a fire mask and an auxiliary prism. The freeform prism includes a total reflection surface S1, a total reflection surface S1', a semi-reflective and semi-transparent surface S2 and a transmission surface S3. The auxiliary prism includes a refractive surface S4.

[0062] The microdisplay emits a light beam, which is refracted to the transmission surface S3 by a double cemented lens. The light beam is then transmitted from the transmission surface S3 to the total reflection surface S1'. The total reflection surface S1' reflects the light beam to the semi-reflective and semi-transparent surface S2. The light beam is then reflected by the semi-reflective and semi-transparent surface S2 to the total reflection surface S1. Finally, the light beam is refracted by the total reflection surface S1 and enters the human eye.

[0063] The beam of light from the real scene passes through the fire hood, and is refracted by the refraction surface S4 to the semi-reflective surface S2. It then passes through the semi-reflective surface S2 and the total reflection surface S1 in sequence before entering the human eye.

[0064] In this embodiment, the microdisplay is an OLED with a resolution of 1920*1080 and a diagonal size of 0.71 inches.

[0065] In this embodiment, the doublet lens is made of a double convex lens and a double concave lens bonded together, including an exit surface S5, a bonding surface S6 and an incident surface S7. The double concave lens is made of EP9000 material and the double convex lens is made of APL5514ML material.

[0066] The light beam emitted by the microdisplay enters the cemented doublet through the incident surface S7 of the biconvex lens, and after being refracted by the cemented surface S6, it exits from the exit surface S5.

[0067] In this embodiment, the distance between the center of the incident surface S7 and the exit surface S5 is less than or equal to 6 mm, and the center thickness of both the biconvex lens and the biconcave lens is not less than 1.2 mm.

[0068] In this embodiment, the freeform prism and the auxiliary prism are both made of COC material, and the fire-fighting mask is made of PC material.

[0069] In this embodiment, the total reflection surface S1, the total reflection surface S1', the semi-reflective and semi-transparent surface S2, and the refractive surface S4 are free-form surfaces, the transmission surface S3 and the exit surface S5 are even-order aspherical surfaces, and the cemented surface S6 and the incident surface S7 are standard surfaces.

[0070] In this embodiment, the total reflection surface S1 is offset from the optical axis by -1.16 mm in the y direction and tilted counterclockwise by 1.63° around the x-axis;

[0071] The semi-reflective and semi-transparent surface S2 is offset from the optical axis by -1.58mm in the y direction and rotates 24.30° clockwise around the x-axis;

[0072] The transmission surface S3 is offset from the optical axis by 17.49 mm in the y direction and rotates counterclockwise by 50.20° around the x-axis;

[0073] The refracting surface S4 is offset from the optical axis by 0.08 mm in the y direction and rotates counterclockwise by 0.63° around the x-axis;

[0074] The emission surface S5 is offset from the optical axis by 19.93 mm in the y direction and rotates counterclockwise by 51.57° around the x-axis.

[0075] In this embodiment, the distance between the total reflection surface S1 and the human eye is less than or equal to 20 mm, the distance between the refractive surface S4 and the fire-fighting mask is less than or equal to 18 mm, and the thickness of the fire-fighting mask is less than or equal to 3 mm.

[0076] Due to the high-temperature tolerance and real-time requirements of firefighting operations, existing optical display systems face severe challenges in high-temperature firefighting scenarios. These challenges primarily manifest as thermal radiation interfering with imaging signals, airborne thermal corona effects causing optical path instability, and a failure to consider the impact of high temperature, thermal radiation, and airborne thermal corona effects on image quality. Furthermore, since light from a fire helmet first passes through the face shield and then is refracted by a prism before entering the eye, the influence of the face shield on the transmitted light path in the fire helmet's optical display system cannot be ignored.

[0077] To address the aforementioned technical issues, this embodiment provides an optical display system for fire helmets based on freeform prisms. By incorporating the fire helmet into the optical design system and optimizing the design of the freeform prism module, the aberrations introduced by the freeform prism are actively compensated during the room temperature design stage, effectively controlling the volume of the freeform prism and making its structure more compact.

[0078] During the design process, a freeform prism module is constructed, including a microdisplay, a doublet lens, a freeform prism, and an auxiliary prism. A three-dimensional optical model of the fire hood is constructed and fitted to a freeform surface. The freeform prism module and the freeform surface fitted to the fire hood are treated as a whole, and the freeform prism module is optimized to obtain the optimized freeform prism module.

[0079] This implementation method employs a reverse design approach, such as... Figure 1 As shown, the actual light rays travel in the opposite direction to the designed light rays. Both the positive and negative edge field principal rays enter from the exit pupil, and the positive and negative edge field principal rays are controlled to prevent interference at any surface, resulting in the optimized freeform prism module. The reverse design method is as follows:

[0080] L is the principal ray of the positive edge field of view. It intersects the total reflection surface S1 of the freeform prism at point A. After refraction, it reaches the semi-reflective and semi-transparent surface S2, where it intersects at point D. After reflection, it reaches the total reflection surface S1', where it intersects at point B. After reflection by the total reflection surface S1', it reaches the refracting surface S3, intersecting with the refracting surface S3 at point C. Finally, it passes through the cemented doublet lens to reach the microdisplay.

[0081] L' is the principal ray of the negative edge field of view. It intersects the total reflection surface S1 of the freeform prism at point G, and after refraction, it intersects the semi-reflective and semi-transparent surface S2 at point F. After reflection, it reaches the total reflection surface S1' and intersects at point H. After reflection by the total reflection surface S1', it intersects the refracting surface S3 at point E, and finally reaches the microdisplay through the cemented doublet lens.

[0082] The principal ray L of the positive edge field of view passes through point D, is refracted by the semi-reflective and semi-transparent surface S2, intersects with the refractive surface S4 of the auxiliary prism at point I, and then exits the auxiliary prism after being refracted by the refractive surface S4.

[0083] The negative edge field of view principal ray L' passes through point F, is refracted by the semi-reflective and semi-transparent surface S2, intersects with the auxiliary prism refraction surface S4 at point J, and then exits the prism after being refracted by the refraction surface S4.

[0084] However, the light displayed by this reverse design method cannot completely simulate the actual light path, especially in the semi-reflective and semi-transparent surface S2. The light path used in the design looks like the light is split into reflected light and transmitted light after passing through the semi-reflective and semi-transparent surface S2. In actual applications, the light entering the human eye in the real scene and the light emitted by the microdisplay overlap at this point. Therefore, in order to prevent interference between the various surfaces, it is necessary to control the position of the intersection point between the light and the surface during the design to prevent interference at the surface edges.

[0085] The freeform prism module optimized based on reverse engineering is as follows:

[0086] like Figure 2 and Figure 3 The diagrams shown illustrate the projection channel and transmission channel of a freeform prism, respectively. The initial structure was obtained by calculating the freeform surface coefficients. Iterative optimization was performed starting with a small aperture at the center field of view, gradually increasing the system's aperture and field of view. After the freeform prism design was completed, a cemented doublet lens was added to eliminate transverse chromatic aberration, thus completing the optimized design of the projection channel. The fire hood was fitted as a freeform surface and integrated into the transmission light path for integrated design. The impact of the fire hood was analyzed, and the auxiliary prism surface was optimized to compensate for aberrations, eliminate excess refractive power and distortion, thus completing the optimized design of the projection channel. Figure 4 As shown, the optimized results show that the MTF of each field of view meets the standard at the Nyquist frequency, and the transverse chromatic aberration is well corrected.

[0087] The freeform prism module consists of a microdisplay, a cemented doublet lens, a freeform prism, and an auxiliary prism. The projection channel of the freeform prism module includes the microdisplay, the cemented doublet lens, and the freeform prism. The projection channel has a total reflection surface S1, a total reflection surface S1', a semi-reflective surface S2, and a transmission surface S3. In practical applications, the light emitted by the microdisplay first passes through the cemented doublet lens, then is refracted through the transmission surface S3 to reach the total reflection surface S1'. After total reflection, it reaches the semi-reflective surface S2 for reflection, and finally is refracted through the total reflection surface S1 to enter the human eye. The light emitted by the microdisplay is magnified and refocused after passing through the cemented doublet lens and the freeform prism, making the image observed by the human eye appear to be composed of an object several meters away, rather than being emitted by the microdisplay which is only a few centimeters away. The microdisplay used is an OLED with a resolution of 1920*1080 and a diagonal size of 0.71 inches.

[0088] The transmission channel of the freeform prism module includes an auxiliary prism and a freeform prism. An auxiliary prism is cemented in front of the freeform prism to correct the distortion and excess refractive power caused by the different optical powers in the x and y directions of the freeform prism. The optical display system of the fire helmet includes a freeform prism module and a fire helmet. External light first passes through the transparent fire helmet, then is refracted by the auxiliary prism refractive surface S4 and reaches the semi-reflective surface S2. Subsequently, it is refracted by the semi-reflective surface S2 and the total reflection surface S1 in sequence and enters the human eye. The semi-reflective surface S2 is provided with a semi-reflective film.

[0089] In this embodiment, a three-dimensional optical model including the fire helmet visor is created in optical simulation software during the initial design phase of the freeform prism module. The three-dimensional optical model should fully consider the material properties, curvature, thickness, and aspherical characteristics of the fire helmet visor. The freeform prism module and the three-dimensional optical model of the fire helmet visor together constitute a complete optical system. The design optimization target is not only aimed at the aberrations of the freeform prism module itself, but also focuses on compensating for and counteracting the refractive power, distortion, and dispersion introduced by the fire helmet visor. Through the aberration correction capability of the freeform surface, the entire optical path is globally optimized, such as... Figure 5 The diagram shown is a schematic of the field curvature and distortion of the transmitted light path with the fire hood after thermal analysis.

[0090] However, in a fire, firefighting masks are exposed to high temperatures. The high temperatures can cause changes in the mask's shape, introducing additional aberrations. When firefighters observe the real scene through the prism, they may experience blurring, defocusing, or image stretching, affecting the imaging quality of the transmitted light path and severely interfering with the consumer's judgment. Existing technologies typically improve the firefighting mask's resistance to deformation by designing the mask and optical display system separately. While this method can reduce the degree of heat deformation, it may increase manufacturing costs or reduce light transmittance, leading to severe degradation of image quality, significantly reduced image contrast and signal-to-noise ratio, and an inability to provide clear, stable, and reliable information in high-temperature firefighting scenarios.

[0091] To address the aforementioned issues, this implementation method employs a calorimetric design for both the projection and transmission channels. In the projection channel, five multi-layered structures ranging from 20°C to 60°C are established using optical design software for thermal analysis. Furthermore, based on the theory of thermal ablation, the optical thermal difference of the system is calculated. During this process, key parameters such as the thermo-optical coefficient dn / dT of the glass material and the linear expansion coefficient α of the lens barrel material need to be consulted. By calculating the contribution weight of each lens to the system's thermal difference, and ultimately by selectively replacing the glass material at key locations, a passive calorimetric design of the system is achieved.

[0092] This embodiment performs finite element analysis on the freeform surface fitted to the fire helmet. Based on the finite element analysis results, a heatless design is performed on the optimized freeform surface prism transmission channel to obtain the final fire helmet optical display system, such as... Figure 6 As shown, by optimizing the auxiliary prism surface, the aberrations caused by the thermal deformation of the fire hood are effectively compensated, making it compatible with existing fire helmets, thereby ensuring that the final fire helmet optical display system maintains high imaging quality over a wide temperature range.

[0093] The design optimization results of the fire helmet optical display system described in this embodiment are as follows:

[0094] The freeform prism and auxiliary prism are made of COC material with good heat resistance and high light transmittance. The COC material has a refractive index of 1.53 and an Abbe number of 56. The cemented doublet includes a biconvex lens and a biconcave lens. The biconcave lens is made of EP9000 material with a low Abbe number of 19 and a high refractive index of 1.67. The biconvex lens is made of APL5514ML material with a high Abbe number of 56 and a low refractive index of 1.54. The light beam emitted by the microdisplay enters the cemented doublet through the incident surface S7 of the biconvex lens, is refracted through the cemented surface S6, and exits from the exit surface S5. The distance between the center of the incident surface S7 and the exit surface S5 is less than or equal to 6 mm. The center thickness of both the biconvex lens and the biconcave lens is not less than 1.2 mm.

[0095] The thickness of the freeform prism and auxiliary prism is less than 15mm, the height is less than 40mm, the width is less than 30mm, the overall FOV (field of view) is more than 45°, the optical structure is compact, the size is small and the weight is light, the focal length of the fire helmet optical display system is 19mm to 20mm, and the conic coefficient of each face does not exceed ±100.

[0096] Total internal reflection surface S1, total internal reflection surface S1', and semi-reflective surface S2 simultaneously transmit and reflect light. Therefore, freeform surfaces are used to increase design freedom. At this point, the optical powers in the x and y directions are different, and the light rays of the real scene observed in the transmitted light path will be stretched, resulting in significant distortion. Therefore, the auxiliary prism refractive surface S4 is also a freeform surface to correct distortion and eliminate unnecessary refractive power. The transmission surface S3 and the exit surface S5 of the cemented doublet lens near the freeform prism are even-order aspherical surfaces. The cemented surface S6 and the incident surface S7 are standard surfaces. The descriptive equation for an even-order aspherical surface is as follows:

[0097] ;

[0098] Where c is the radius of curvature, k is the conic coefficient, and A i is the coefficient of the aspherical term, r is the radial distance, and i is the number of aspherical terms;

[0099] The S2 type of the semi-reflective, semi-transparent surface used in the freeform prism is an XY polynomial, and its describing equation is as follows:

[0100] ;

[0101] in, j It is the term number of the polynomial. C j For freeform surfaces j The coefficients corresponding to the terms, x and y are rectangular coordinates defined on the aperture plane of the optical element, and m and n are the terms of the first and second terms. j The exponents of x and y in the term;

[0102] During the design process, since the overall structure is symmetrical about the YOZ plane, the coefficients with odd-degree x terms are set to zero. The freeform prism module has a certain degree of eccentricity and tilt. The total reflection surface S1 is deviated from the optical axis by -1.162mm in the y direction and tilted counterclockwise by 1.63° around the x axis.

[0103] The semi-reflective and semi-transparent surface S2 is offset from the optical axis by -1.58mm in the y direction and rotates 24.3° clockwise around the x-axis;

[0104] The transmission surface S3 is offset from the optical axis by 17.49 mm in the y direction and rotated counterclockwise by 50.2° around the x-axis;

[0105] The refractive surface S4 is offset from the optical axis by 0.08 mm in the y direction and rotates counterclockwise by 0.625° around the x-axis;

[0106] The exit surface S5 is offset from the optical axis by 19.932 mm in the y direction and rotates counterclockwise by 51.566° around the x-axis.

[0107] The distance between the human eye and the total internal reflection surface S1 of the freeform prism (exit pupil distance) shall not exceed 20 mm, and the distance between the refractive surface S4 and the fire-fighting mask shall not exceed 18 mm.

[0108] The light rays passing through the total internal reflection surface S1 must satisfy the condition of total internal reflection. The refractive index of the COC material used in the freeform prism is 1.53, therefore... .

[0109] In this embodiment, finite element analysis is performed on the fire-fighting face shield using thermal analysis software to simulate its thermal deformation under high-temperature conditions, such as... Figure 7 and Figure 8As shown, the surface shape change after heating is observed. Based on the finite element analysis results, the heated fire mask is fitted into a freeform surface, and the corresponding three-dimensional optical model is constructed. In the freeform surface term fitted by the mask, Y1=0.065, X2=-0.011, Y2=-0.0044, X2Y1=7.59E-006, and Y3=2.61E-006. This 3D optical model accurately reflects the actual surface shape of the fire-fighting mask under high temperatures, providing a foundation for athermal design. Integrating this model into the overall optical display system of the fire helmet improves the compatibility between the helmet and the prism, as well as the overall system's applicability in various application scenarios. This integrated design eliminates the need to improve the mask's deformation resistance; only the optical system needs modification based on the mask's surface shape changes after heating. This achieves clear and stable imaging quality in application scenarios ranging from 20℃ to 60℃, ensuring that images of real-world scenes appear without geometric distortion to the human eye, precisely matching real-world coordinates, eliminating blurring and stretching at image edges, guaranteeing clarity across the entire field of view, compensating for chromatic aberration generated by the mask and prism themselves, and preventing colored fringing at virtual image edges. Furthermore, the system exhibits better adaptability, effectively utilizing the space within the mask for a more compact structure. The athermal design of the optical system stabilizes image quality within the operating temperature range, reduces MTF fluctuations, and effectively corrects overall system thermal differences. In the projection channel, the contribution weight of each optical surface to the system's thermal difference is calculated, precisely identifying the materials that need to be replaced, such as... Figure 9 and Figure 10 The diagram shows the MTF (Mean Transformation Factor) before and after thermal analysis of the projection channel. In the transmission channel, the aberrations caused by the thermal deformation of the fire hood were compensated by optimizing the auxiliary prism surface. Figure 11 and Figure 12 The figure shows a schematic diagram of the MTF with the transmission channel of the fire mask before and after thermal analysis, where the OTF modulus is the optical transfer function modulus.

[0110] Through the design of the optical display system for fire helmets, the overall distortion of the freeform prism projection channel does not exceed 11.5%, and the transverse chromatic aberration is less than 5μm. Figure 13 and Figure 14 As shown, in the application scenario, the entire fire helmet optical display system operates within a temperature range of 20°C to 60°C, and has heat differential insulation capabilities. The fire helmet face shield is made of PC material, and its thickness does not exceed 3mm. Figure 15 The diagram shown is a point graph after the system design optimization.

[0111] Therefore, this implementation breaks away from the traditional approach of separating AR display design from helmet protection design, proposing a new paradigm of integrated "display-mask" design. It integrates the optical display system of the fire helmet with a projection module, light-emitting element, and lens module group. By optimizing the design of the freeform prism module and focusing on the thermal analysis results of the fire helmet, a thermal analysis was conducted on the optimized optical system. This solves the problems of image quality degradation (such as image blurring and distortion) caused by the optical prism being easily heated in high-temperature fire environments, as well as the image quality reduction caused by changes in the surface shape of the fire helmet due to heat. Wavefront aberration is effectively suppressed, so that the virtual information ultimately perceived by the human eye and the real scene seen through the same fire helmet are visually perfectly integrated, and the clarity is improved. This greatly enhances the operational flexibility and user experience of firefighters in long-term high-intensity missions. Furthermore, while improving the AR display function, no protective performance (impact resistance, fire resistance, chemical protection) of the fire helmet is sacrificed, achieving a unity of functional enhancement and safety assurance.

[0112] Implementation Method 2

[0113] A design method for an optical display system for fire helmets based on freeform prisms, the method being used to construct the system described in Embodiment 1, includes the following steps:

[0114] Step 1: Construct a freeform prism module, including a microdisplay, a cemented doublet lens, a freeform prism, and an auxiliary prism. Construct a three-dimensional optical model of the fire hood and fit it to a freeform surface.

[0115] Step 2: Taking the freeform prism module and the fire hood as a whole, optimize the design of the freeform prism module to obtain the optimized freeform prism module.

[0116] Step 3: Perform finite element analysis on the freeform surface fitted by the fire helmet described in Step 1. Based on the finite element analysis results, perform a heatless design on the optimized freeform surface prism module to obtain the final fire helmet optical display system.

[0117] The optimization design of the freeform prism module and the thermal design of the optimized freeform prism module both employ a reverse design method. The positive and negative edge field-of-view principal rays are incident on the freeform prism module from the exit pupil position, and interference between the positive and negative edge field-of-view principal rays is controlled to prevent them from interfering with each surface. Specifically:

[0118] ;

[0119] ;

[0120] Among them, Y BLet Y be the coordinate of point B in the Y direction. C Let C be the coordinates of point C in the Y direction, and Z be the coordinates of point C in the Z direction. B Let B be the coordinate of point B in the Z direction, Z C Let C be the coordinates of point C in the Z direction;

[0121] ;

[0122] ;

[0123] Among them, Y D Let D be the coordinate of point D in the Y direction, Y E Let E be the coordinate of point E in the Y direction, Z... D Let D be the coordinates of point D in the Z direction, Z E Let E be the coordinate of point E in the Z direction;

[0124] ;

[0125] ;

[0126] Among them, Y I Let I be the coordinate of point I in the Y direction, Y E Let E be the coordinate of point E in the Y direction, Z... I Let I be the coordinate of point I in the Z direction, Z D Let D be the coordinates of point D in the Z direction;

[0127] ;

[0128] ;

[0129] ;

[0130] Among them, Y F Let F be the coordinate of point F in the Y direction, Y G Let G be the coordinates of point G in the Y direction, Z... F Let F be the coordinate of point F in the Z direction, Z G Let G be the coordinates of point G in the Z direction, Y... H Let H be the coordinates of point H in the Y direction, Y G Let G be the coordinates of point G in the Y direction.

[0131] Implementation Method 3

[0132] This embodiment is a specific implementation based on the fire helmet optical display system based on a freeform prism described in Embodiment 1 and the design method of the fire helmet optical display system based on a freeform prism described in Embodiment 2. Specifically, it is as follows:

[0133] In this embodiment, the field of view of the freeform prism projection channel is 39°(H)*23°(V), and the diagonal field of view is 45°. The diagonal field of view of the transmission channel is 22.5°(H)*12.5°(V), and the diagonal field of view is 51°. The exit pupil diameter is 8mm. The MTF value of the transmission channel at the Nyquist frequency is greater than 0.3, the distortion is less than 5%, and the grid distortion is less than 11%.

[0134] See the table below for specific parameters:

[0135] Table 1

[0136]

[0137] Table 2

[0138]

[0139] Table 3

[0140]

[0141] Table 4

[0142]

[0143] Table 5 Fitting surface coefficients of fire helmet face shields

[0144]

[0145] The design method of the fire helmet optical display system based on freeform prism proposed in this invention has been described in detail above. Specific examples have been used to illustrate the principle and implementation of this invention. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method of designing a firefighting helmet optical display system based on a freeform prism, characterized in that, The method comprises the following steps: Step 1, constructing a free-form surface prism module, including a micro display, a double-cemented lens, a free-form surface prism and an auxiliary prism, constructing a three-dimensional optical model of a mask, and fitting the three-dimensional optical model into a free-form surface; Step 2, fitting the free-form surface prism module and the mask into a free-form surface as a whole, and optimizing the free-form surface prism module to obtain an optimized free-form surface prism module; Step 3, performing finite element analysis on the free-form surface fitted by the mask in step 1, and combining the finite element analysis result to perform athermalization design on the optimized free-form surface prism module to obtain a final fire helmet optical display system; The fire helmet optical display system comprises a micro display, a double-cemented lens, a free-form surface prism, a mask and an auxiliary prism, the free-form surface prism comprises a total reflection surface S1, a total reflection surface S1', a half-reflection half-transmission surface S2 and a transmission surface S3, and the auxiliary prism comprises a refractive surface S4; The micro display emits a light beam, the double-cemented lens is used to refract the light beam to the transmission surface S3, the transmission surface S3 is used to transmit the light beam to the total reflection surface S1', the total reflection surface S1' is used to totally reflect the light beam to the half-reflection half-transmission surface S2, the half-reflection half-transmission surface S2 is used to reflect the light beam to the total reflection surface S1, and the total reflection surface S1 is used to refract the light beam into a human eye; The light beam of a real scene passes through the mask, the refractive surface S4 is used to refract the light beam of the real scene to the half-reflection half-transmission surface S2, and the light beam is refracted into the human eye in sequence through the half-reflection half-transmission surface S2 and the total reflection surface S1; The total reflection surface S1 deviates from an optical axis by -1.162 mm in a y direction, and is inclined counterclockwise by 1.63° around an x axis; The half-reflection half-transmission surface S2 deviates from the optical axis by -1.58 mm in the y direction, and is rotated clockwise by 24.3° around the x axis; The transmission surface S3 deviates from the optical axis by 17.49 mm in the y direction, and is rotated counterclockwise by 50.2° around the x axis; The refractive surface S4 deviates from the optical axis by 0.08 mm in the y direction, and is rotated counterclockwise by 0.625° around the x axis; An exit surface S5 in the double-cemented lens deviates from the optical axis by 19.932 mm in the y direction, and is rotated counterclockwise by 51.566° around the x axis; The total reflection surface S1 and the total reflection surface S1' have a curvature radius of 560, the half-reflection half-transmission surface S2 has a curvature radius of -274.9, the transmission surface S3 has a curvature radius of -12.39, the refractive surface S4 has a curvature radius of -171.7, the exit surface S5 in the double-cemented lens has a curvature radius of -18.937, a cemented surface S6 has a curvature radius of 124.6, and an entrance surface S7 has a curvature radius of -19.

12.

2. The free-form prism based optical display system design method for firefighting helmets according to claim 1, characterized in that, The double-cemented lens is formed by cementing a double-convex lens and a double-concave lens, and comprises the exit surface S5, the cemented surface S6 and the entrance surface S7, the double-concave lens is made of EP9000 material, and the double-convex lens is made of APL5514ML material; The light beam emitted by the micro display enters the double-cemented lens through the entrance surface S7 of the double-convex lens, is refracted after the cemented surface S6, and is emitted from the exit surface S5.

3. The freeform prism based optical display system design method for firefighting helmets according to claim 2, wherein, The center of the entrance surface S7 is less than or equal to 6 mm away from the exit surface S5, and the center thicknesses of the double-convex lens and the double-concave lens are both not less than 1.2 mm.

4. The free-form prism based optical display system design method for firefighting helmets according to claim 1, wherein, The free-form surface prism and the auxiliary prism are COC materials, and the mask is a PC material.

5. The freeform prism based optical display system design method for firefighting helmets according to claim 2, wherein, The total reflection surface S1, the total reflection surface S1', the half reflection and half transmission surface S2 and the refraction surface S4 are free-form surfaces, the transmission surface S3 and the exit surface S5 are even aspheric surfaces, and the cement surface S6 and the entrance surface S7 are standard surfaces.

6. The free-form prism based optical display system design method for firefighting helmets according to claim 1, wherein, The distance between the total reflection surface S1 and the human eye is less than or equal to 20 mm, the distance between the refraction surface S4 and the mask is less than or equal to 18 mm, and the thickness of the mask is less than or equal to 3 mm.

7. The free-form prism based firefighting helmet optical display system design method of claim 1, wherein, The mask fits the free surface term Y1 = 0.065, X2 = -0.011, Y2 = -0.0044, X2Y1 = 7.59 x 10 -6 , Y3 = 2.61 x 10 -6 .

8. The free-form prism based firefighting helmet optical display system design method of claim 1, wherein, The optimization design of the free-form surface prism module in the step 2 and the athermalization design of the optimized free-form surface prism module both adopt a reverse design method, the positive direction edge field chief ray and the negative direction edge field chief ray of the free-form surface prism module are shot from the exit pupil position, and the positive direction edge field chief ray and the negative direction edge field chief ray are controlled not to interfere with each other at each surface, and the specific process is as follows: ； ； wherein Y B is the coordinate of point B in the Y direction, Y C is the coordinate of point C in the Y direction, Z B is the coordinate of point B in the Z direction, Z C is the coordinate of point C in the Z direction, B is the intersection of the positive edge field chief ray and the total reflection surface S1', and C is the intersection of the positive edge field chief ray and the refractive surface S3. ； ； wherein Y D is the coordinate of point D in the Y direction, Y E is the coordinate of point E in the Y direction, Z D is the coordinate of point D in the Z direction, Z E is the coordinate of point E in the Z direction, D is the intersection of the chief ray of the positive direction edge field of view with the semi-reflective semi-transmissive surface S2, and E is the intersection of the chief ray of the negative direction edge field of view with the refractive surface S3. ； ； wherein Y I is the coordinate of point I in the Y direction, Y E is the coordinate of point E in the Y direction, Z I is the coordinate of point I in the Z direction, Z D is the coordinate of point D in the Z direction, and I is the intersection of the chief ray of the positive edge field of view and the auxiliary prism refracting surface S4. ； ； ； wherein Y F is the coordinate of the F point in the Y direction, Y G is the coordinate of the G point in the Y direction, Z F is the coordinate of the F point in the Z direction, Z G is the coordinate of the G point in the Z direction, Y H is the coordinate of the H point in the Y direction, Y G is the coordinate of the G point in the Y direction, the F point is the intersection of the chief ray of the negative direction edge field of view with the half reflection half transmission surface S2, the G point is the intersection of the chief ray of the negative direction edge field of view with the total reflection surface S1, and the H point is the intersection of the chief ray of the negative direction edge field of view with the total reflection surface S1’.

Images