Novel safety warning device

Abstract

The utility model provides a novel safety warning device which is composed of multiple layers of materials, namely a base material layer, a visible light visual material layer, a broadband wavelength selective reflecting layer, a corner reflector structure layer and a protective layer from the bottom layer to the outermost layer in sequence. Wherein the broadband wavelength selective reflecting layer is a wavelength selective reflecting film formed by a plurality of layers of dielectric materials, is transparent to visible light, and has extremely high reflectivity to light in a working wave band of the vehicle-mounted laser radar; the corner reflector structure layer comprises a miniature rectangular prism, and laser radar signals can be effectively reflected back to an emission source of the corner reflector structure layer in a wide incidence angle range. By applying the safety warning device, the reflectivity and the retroreflection effect of the safety warning device under the two main laser radar working wavelengths of 905 nanometers and 1550 nanometers can be greatly improved, meanwhile, the visual characteristics required by human recognition are kept, and the running safety and reliability of an intelligent / automatic driving automobile are improved.

Description

A new type of safety warning device Technical Field

[0001] This utility model relates to safety warning devices, and more particularly to a novel safety warning device that can significantly improve the detection range of vehicle-mounted lidar. Background Technology

[0002] Current traffic safety signs are primarily designed for human drivers, relying on visual stimuli such as color, shape, and reflectivity in the visible spectrum. However, intelligent vehicles equipped with advanced driver assistance systems (ADAS) or autonomous driving systems utilize various sensor technologies to identify road conditions, obstacles, and signs, with lidar (light detection and ranging) being a key component of perception and navigation. LiDAR systems determine distance by emitting laser pulses and measuring the time it takes for them to reflect back to the sensor, generating detailed point clouds. AI algorithms then accurately map the surrounding environment in 3D, enabling obstacle detection and object classification, thus achieving autonomous obstacle avoidance and navigation. Intelligent driving vehicles need to visualize, understand, and react to the surrounding world to operate safely, and lidar is one of the key sensors for achieving this first step. However, lidar systems are not optimally suited for detecting road signs, especially temporary warning devices such as traffic cones. This is mainly due to differences in sensor type and operating wavelength between human vision and lidar technology. Human vision is sensitive to visible light (approximately 400-700 nm wavelengths), while automotive lidar typically operates in the near-infrared (NIR) spectrum, with primary operating wavelengths of 905 nm and 1550 nm. Current vehicle-mounted lidar technology typically has a detection range of over 100 meters for cars ahead, but for small objects such as cones or temporary speed limit signs, the detection range is less than 100 meters, which is inferior to that of human drivers. This distance cannot provide sufficient safety in highway scenarios.

[0003] Therefore, with the rapid development and increasing popularity of intelligent driving and autonomous vehicle technologies, it has become crucial to reassess existing road infrastructure (including safety warning signs). This includes optimizing the near-infrared (NIR) spectral reflectance characteristics of safety warning devices to improve their effective detection range by lidar, including safety warning signs, speed limit signs, cones, temporary traffic deflectors, and other similar devices.

[0004] This invention addresses the shortcomings of the aforementioned safety warning signs, particularly those used in highway scenarios, by proposing a novel safety warning device that effectively improves the detection range of vehicle-mounted lidar. This device employs a multi-medium coating to provide excellent reflectivity and retroreflective characteristics within the lidar's operating wavelength band, significantly enhancing the detection capability of the vehicle-mounted lidar system while maintaining visual effectiveness for the human driver. Summary of the Invention

[0005] This invention proposes a novel safety warning device, which is composed of multiple layers of materials. From the bottom layer to the outermost layer, the layers are: a base material layer, a visible light visual material layer, a broadband wavelength selective reflective layer, a corner reflector structure layer, and a protective layer. The broadband wavelength selective reflective layer is a wavelength selective reflective film composed of multiple layers of dielectric materials, which is transparent to visible light and has extremely high reflectivity for light in the operating wavelength range of vehicle-mounted lidar. The corner reflector structure layer contains miniature right-angle prisms, which can effectively reflect lidar signals back to their source within a wide range of incident angles.

[0006] Preferably, the multilayer dielectric material includes a dielectric material with a low refractive index and a dielectric material with a high refractive index, which are arranged alternately according to their refractive indices to form a periodic multilayer structure, which together constitute the wavelength selective reflective film.

[0007] Preferably, the medium material with a lower refractive index includes silicon dioxide or magnesium fluoride, and the medium material with a higher refractive index includes titanium dioxide, tantalum pentoxide, or zinc sulfide.

[0008] Preferably, the operating wavelength band of the vehicle-mounted lidar is 905nm and 1550nm.

[0009] Preferably, the base material layer is made of plastic, rubber, or metal.

[0010] Preferably, the visible light visual material layer includes a warning color paint coating and a reflective layer composed of a microprism structure, which contains warning patterns and text.

[0011] Preferably, the protective layer is a transparent polymer, including polycarbonate or polymethyl methacrylate.

[0012] Preferably, the novel safety warning device is a traffic safety warning sign, a speed limit sign, a cone-shaped safety cylinder, or a temporary deflector.

[0013] This invention employs a multi-medium coating and corner reflector structure to provide excellent reflectivity and retroreflection characteristics in the operating band of lidar, greatly enhancing the detection capability of the vehicle-mounted lidar system while maintaining the visual effectiveness for the human driver.

[0014] Other features and advantages of this utility model will become clearer after reading the detailed description of the embodiments of this utility model in conjunction with the accompanying drawings. Attached Figure Description

[0015] To clearly illustrate the technical solution and embodiments of this utility model, the accompanying drawings are briefly described below. It should be noted that the drawings are primarily intended to explain the interconnections, structural features, and advantages of the various components of the device, and are not drawn to scale according to the actual dimensions of the device. Obviously, the drawings only relate to a limited set of embodiments and should not be construed as limiting the present utility model. Those skilled in the art can easily obtain new embodiments through formal variations based on these drawings.

[0016] Figure 1 is a schematic diagram of a commonly used conical safety cylinder structure;

[0017] Figure 2 is a structural schematic diagram of an embodiment of the present invention;

[0018] Figure 3 is a structural schematic diagram of another embodiment of the present invention;

[0019] Figure 4 is a graph showing the reflection coefficient of the wavelength-selective reflective film as a function of wavelength in one embodiment of this utility model;

[0020] Figure 5 is a layered structural diagram of another embodiment of this utility model. Detailed Implementation

[0021] The specific embodiments of this utility model are described in detail below with reference to the accompanying drawings.

[0022] The design and material selection of existing highway safety warning devices are primarily geared towards human driver visual perception. Figure 1 shows a schematic diagram of a common safety warning device—a traffic cone / conical safety cylinder. A large area of ​​the conical plastic body is coated with orange, red, or yellow warning colors (A1), supplemented by a reflective strip (A2) based on glass beads or microprisms. While these devices exhibit good reflectivity in the visible light range, their performance is insufficient in the near-infrared spectral range where intelligent driving vehicle lidar systems operate, leading to problems with insufficient recognition distance and low accuracy. LiDAR detection relies on the intensity of the target object's reflection of the laser pulse. If the material of the warning sign has low reflectivity at the lidar's operating wavelength (e.g., 905 nm or 1550 nm), the signal strength returning to the lidar sensor will be weakened, resulting in a shorter detection distance. Many traditional pigments and coatings used to produce visible colors may have different optical properties in the near-infrared spectral range, and may even absorb near-infrared light. Currently, reflective materials used to improve nighttime human visibility, such as reflective strips on traffic cones, typically employ glass bead or microprism-based technologies. These materials perform well in the visible light range, but their reflectivity may be low in the near-infrared wavelength range. The reflectivity of glass beads is closely related to the refractive index of the incident medium; glass beads optimized for visible light may not provide optimal reflectivity in the near-infrared wavelength range. For high-speed autonomous vehicles, insufficient detection distance directly impacts driving safety. If lidar cannot detect temporary speed reduction warnings or lane-guiding cones at a sufficient distance, vehicles may not be able to react in time, leaving too little time for driver intervention, thus increasing the risk of accidents. Especially for smaller objects like traffic cones, which occupy fewer points in the lidar point cloud, insufficient reflectivity makes them more susceptible to misjudgment or missed detection. Furthermore, existing warning sign designs, such as colors and patterns, are optimized for the human visual system. Lidar systems rely not only on reflectivity but may also utilize information about the object's shape and size for object recognition. However, if the reflection characteristics of the warning sign are not uniform at the LiDAR wavelength, or if the point cloud is sparse due to the distance, the LiDAR system may have difficulty accurately extracting the shape and size information of the object, thus affecting the recognition accuracy.

[0023] To address the limitations of existing safety warning signs in LiDAR detection for intelligent driving vehicles, this invention proposes a novel safety warning device. This solution employs a multi-medium coating to significantly improve reflectivity and retroreflection near common automotive LiDAR operating wavelengths (905 nm and 1550 nm), while also considering the visual needs of human drivers. The multi-medium coating consists of multiple ultra-thin layers, each composed of materials with specific optical properties. The selection of these materials and the thickness of each layer are precisely designed to utilize the principle of optical interference to achieve high reflectivity and retroreflection within the LiDAR's operating wavelength range, ensuring that the LiDAR system can detect the warning sign at long distances with high precision. This invention creates a "dual-modal" effective warning sign that meets the stringent requirements of machine vision while conforming to the traditional perception and visual habits of human drivers regarding safety warning signs, thereby improving the safety of autonomous driving without compromising existing road safety standards.

[0024] When light waves propagate at the interface between two media with different refractive indices, some light is reflected and some is transmitted. In multilayer thin films, light waves are reflected at each interface, and these reflected light waves interfere with each other, producing constructive interference (peaks align with peaks, troughs align with troughs, thus enhancing light intensity) or destructive interference (peaks align with troughs, thus weakening or canceling light intensity). By precisely controlling the thickness of each layer in a multilayer thin film, the optical properties of the film can be "tuned," for example, achieving high reflectivity at a specific target wavelength. To achieve high reflectivity at a specific wavelength, multilayer coatings typically employ the principle of constructive interference. This is usually achieved by using dielectric coatings composed of alternating layers of high and low refractive index materials. When the optical thickness of each layer (the product of physical thickness and refractive index) is designed to be one-quarter of the target wavelength (λ / 4n), the reflected light from each interface will be in phase and undergo constructive interference, resulting in a significant increase in overall reflectivity at that wavelength. By carefully optimizing the structure of multilayer films, high reflectivity over a wide wavelength range can be achieved.

[0025] To achieve high reflectivity in the near-infrared spectral range, particularly for the two main lidar operating wavelengths of 905 nm and 1550 nm, the multilayer coating utilizes materials with high refractive index contrast at these wavelengths. These materials include silicon dioxide (SiO2) and magnesium fluoride (MgF2) with low refractive indices, and titanium dioxide (TiO2), tantalum pentoxide (Ta2O5), or zinc sulfide (ZnS) with high refractive indices. These materials exhibit transmission characteristics in the visible light band. The coating thickness is precisely calculated based on the quarter-wavelength stacking principle (optical thickness = λ / 4 * n, where λ is the target wavelength and n is the refractive index of the material at that wavelength). The two multilayer dielectric films B1 and B2 designed accordingly exhibit high reflectivity at wavelengths of 905 nm and 1550 nm, respectively, while remaining completely transparent to visible light. By bonding these two dielectric films alternately to a conical safety cylinder, a conical safety cylinder with extremely high reflectivity to vehicle-mounted lidar signals is formed. Simultaneously, because it is transparent to visible light, it does not affect the original visible light visual effect of the conical safety cylinder, and will not affect the traditional perception and visual habits of human drivers regarding safety warning signs. Figures 2 and 3 respectively show two embodiments, where the two multilayer dielectric films B1 and B2 are distributed in a ring-like pattern from top to bottom on the side of the cone, as shown in Figure 2, or distributed alternately along the generatrix on the side of the cone, as shown in Figure 3.

[0026] To further improve the ease of fabrication of safety warning devices, a periodic structure can be formed using alternating layers of high and low refractive index materials to create a broadband wavelength-selective reflective film. This film achieves high reflectivity at both 905 nm and 1550 nm while remaining transparent to visible light. Figure 4 shows the reflectivity versus wavelength of one embodiment. As can be seen from the figure, the reflectivity of this multilayer dielectric film is greater than 99.9% from 900 nm to 1650 nm. By attaching this reflective film to the surface of the original safety warning device, the reflectivity of the safety warning device to vehicle-mounted lidar signals can be greatly improved while maintaining the original visible light visual effect.

[0027] To further improve the detectability of the safety warning device against vehicle-mounted LiDAR, a tiny corner reflector structure layer can be designed on the surface of the aforementioned broadband wavelength selective reflective film. These tiny three-sided right-angle prisms can effectively reflect light back to its source over a wide range of incident angles. This achieves a retroreflection effect against the LiDAR. To protect the corner reflector structure layer, a transparent polymer, such as polycarbonate (PC) or polymethyl methacrylate (PMMA), can be coated on its surface. These materials have good optical transparency and mechanical properties, and are used to fill the cavities of the cubic corner structure, increasing the structure's stability and optical performance. Figure 5 shows a schematic diagram of the layered structure of a safety warning device. C1 is the base material layer of the safety warning device, such as plastic, rubber, or metal; C2 is the visible light visual material layer, including a warning color paint coating and a reflective layer composed of microprisms, which bear warning patterns and text; C3 is the broadband wavelength selective reflective film, transparent to visible light and exhibiting extremely high reflectivity for 905nm and 1550nm lasers; C4 is the corner reflector structure layer, containing micro-right-angle prisms that can effectively reflect lidar signals back to their source over a wide range of incident angles; and C5 is the protective layer composed of a transparent polymer.

[0028] The description of this utility model is given for illustrative purposes only and is not intended to be exhaustive or to limit the utility model to the disclosed forms. The embodiments were chosen and described to better illustrate the principles and practical applications of this utility model, and to enable those skilled in the art to understand this utility model and design various embodiments with various modifications suitable for specific applications. All new embodiments that fall within the basic concept, construction principles, and spirit of this utility model, and are achieved through simple variations, modifications, equivalent substitutions, or improvements, should be included within the protection scope of this utility model. For example, if an embodiment of this utility model is a conical safety cylinder, similarly, this utility model can also be used for road traffic safety facilities such as traffic safety warning signs, speed limit signs, and temporary traffic dividers. The scope of this utility model is defined by the appended claims.

Claims

1. A novel safety warning device, characterized in that, The novel safety warning device is composed of multiple layers of materials, from the bottom to the outermost layer, consisting of a base material layer, a visible light visual material layer, a broadband wavelength selective reflective layer, a corner reflector structure layer, and a protective layer. The broadband wavelength selective reflective layer is a wavelength selective reflective film composed of multiple layers of dielectric materials, which is transparent to visible light and has extremely high reflectivity to light in the operating band of the vehicle-mounted lidar. The corner reflector structure layer contains miniature right-angle prisms, which can effectively reflect lidar signals back to their source over a wide range of incident angles.

2. The novel safety warning device according to claim 1, characterized in that, The multilayer dielectric material includes dielectric materials with low refractive index and dielectric materials with high refractive index, which are arranged alternately according to their refractive index to form a periodic multilayer structure, which together constitute the wavelength selective reflective film.

3. The novel safety warning device according to claim 2, characterized in that, The lower refractive index medium material includes silicon dioxide or magnesium fluoride, and the higher refractive index medium material includes titanium dioxide, tantalum pentoxide, or zinc sulfide.

4. The novel safety warning device according to claim 1, characterized in that, The operating wavelengths of the vehicle-mounted lidar are 905nm and 1550nm.

5. The novel safety warning device according to claim 1, characterized in that, The base material layer is made of plastic, rubber, or metal.

6. The novel safety warning device according to claim 1, characterized in that, The visible light visual material layer includes a warning color paint coating and a reflective layer composed of a microprism structure, which contains warning patterns and text.

7. The novel safety warning device according to claim 1, characterized in that, The protective layer is a transparent polymer, including polycarbonate or polymethyl methacrylate.

8. The novel safety warning device according to any one of claims 1-7, characterized in that, The new safety warning devices include traffic safety warning signs, speed limit signs, cone-shaped safety cylinders, and temporary deflectors.

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