Dual-eyebox Head-up Display

Transcription

1 Dual-eyebox Head-up Display Chun-Yao Shih Research and Development Division Automotive Research & Testing Center Changhua, Taiwan (R.O.C.) Cheng-Chieh Tseng Research and Development Division Automotive Research & Testing Center Changhua, Taiwan (R.O.C.) Abstract Regardless of the designs, the present optical designs for head-up display (HUD) focus mainly on the optical path structure, which results in large and far virtual images, and a reduction in size. However, after optical amplification, the display range and size will be limited and reduced that limits the driver s vision to a specific area. In order to solve the problems of the existing structure, this study uses imaging design as the development target and applies the capability of optical simulation design to perform ray tracing simulation. By doing so, this can solve the aberration problem caused by the limitations of the off-axis and space configurations. The specially designed laminated combiner allows the optical system to achieve the effect of multiple display ranges. The output specifications are two eyeboxes with dimensions of 90x120mm, a virtual image distance of 2,000mm, a magnification factor of about 4x, and a maximum distortion value not exceeding 5%. Keywords- Optical Design; Dual-eyebox; Head-up Display I. INTRODUCTION If the driver wants to read the information from the dashboard when he is looking straight ahead, it takes time to change the eye focus between the road and the dashboard, causing potential danger when the focal length shifts and the line of sight does not stay on the road, which an accident may occur as a result. The HUD has the characteristics that the on-vehicle display can be viewed at the same time as well as the front view. The driver can see the information presented on the HUD without leaving sight of the road ahead. This function is very useful for the display of vehicle-related information because it allows drivers to obtain important information while paying attention to the traffic [1]. The system projects information onto a laminated combiner, allowing important information to be displayed to the driver through virtual images, and simultaneously allowing the driver to maintain eye contact on the road to increase safety [2]. HUDs on the market includes Windshield-HUD (W-HUD), Combiner-HUD (C-HUD), and AR-HUD. The optical technologies of the W-HUD and the C-HUD are similar. The main difference between the two is that the W-HUD uses the windshield as a combiner, therefore limiting the optical amplification and would require a larger space for the opto-mechanical body. To meet the requirement, automakers would have to reserve space to contain it. Some automobile manufacturers factor in the marketability of the HUDs. Factors include how well the acceptance of the technology is, the size, the cost, and the the feasibility of installation space. With these factors, the technical layout of the C-HUD is more preferable [3]. Figure 1. Head-up Display show image in front of view. In general HUDs, the problem of different heights among drivers is usually solved by adjusting the angle of the combiner [4], which results in insufficient operability and visual comfort. In order to cope with different heights, this study designs a HUD with multiple displays in order to strengthen the information readability of HUD. The distance between two pupils of the human eye is about 65 mm. The more comfortable eyebox is usually set to 90*60 mm. However, it is difficult to maintain in the same head position while driving. Normally, there are several occasions that yield several centimeters between the head and the headrest, such as: leaning forward to operate switches on the dashboard, looking back and other temporary motions, resulting in a distance between the head and the headrest greater than 15 cm. While resting on the headrest, the distance is 0 cm. Under these three situations, the height of the human eye will change. The width of 60 mm is usually only suitable for one of the situations, while having multiple eyeboxes allow the driver to obtain information more often. Enhancing the wide-view and far-pitch virtual image system of the HUD is one of the goals for the improvement of the system s technology. Another goal is to strike a balance between optical performance and the size of optical machine, so by installing the HUD in the vehicle would provide clearer images for the driver.

2 II. THE PRINCIPLE The purpose of the design is to use a dual-eyebox laminated image to achieve two eyeboxes, so that under a single HUD system, drivers of different heights can read images. Conventional laminated image has a single eyebox, meaning people with different heights or postures would have to readjust the laminated image. This new design has 2 eyeboxes for different heights to see the image on the HUD. The problem of double image will reduce the readability of the HUD, and would lead to comfort and safety issues. The problem would become more serious [5] especially when the display content of modern vehicle-mounted HUDs becomes more and more abundant. The optical design of this study is the reverse application of the double image problem caused by the laminated windshield. This would first solve the double image problem. Then secondly, there can be two eyeboxes. In this optical design, the off-axis and concave lens properties of the second reflector must be compensated to ensure image visibility. Because the interpupillary distance is very small compared to the image, the distance of the double image in the horizontal direction is usually ignored, so the double image only needs to process the light path perpendicular to the direction of the ground [6]. Figure 2. Head-up Display structure. The display system uses a LASER light source micro projector, mainly because of the high directivity of the LASER light source, the design can be miniaturized, and the design requirements can be used throughout the day. The system uses a LASER light source for design, and the overall structure includes an image source, amplifying components, and a virtual image opto-mechanical structure. The system uses a LASER scanning micro projector as an image source, places an imaging element to image the light projected by the projector in front, and then uses a lens and a semi-transmission laminated combiner to complete the design. It can be processed by using a pre-tilt design [7]. Design focus: using the first image component to form an image on an imaging surface, and set a lens group behind the imaging surface to enlarge the imaging and limit the size of field of view. Then adopt a concave surface of the semi-transmissivity laminated combiner design to enlarge the image and project it to 2 meters in front of human eyes. The overall system reduces the number of components to maximize its output brightness. III. DESIGN The image produced by the internal reflection on the outer side of the optical element is called ghost image, which interfere person with the image generated from the optical inner surface [8]. The ghosting problem is difficult to solve. Mechanical adjustments, systematic errors, and changes in windshield curvature can cause ghost images to appear [9], [10]. The optical system will use ZEMAX as the optical simulation software, where the key factors of optical design include: virtual image distance, virtual image size, eyebox size, image quality, etc. [11]. The system uses a small-sized LASER micro projector and a screen as an image source, and then places optical components to convert the real image into an enlarged and farther virtual image for human eyes to view information. The HUD is composed of a display module and an optical component. The display module provides the image source to be displayed, and the image source is projected onto the combiner through the optical system for viewing by the driver. The system display module uses a LASER micro projector as the image source, and its features are high brightness, high color rendering, and high black reproducibility. The optical system will use the optical simulation software ZEMAX for simulation design. The expected goal is to design the image to be enlarged and projected to 2 meters in front of the human eye, reduce the components of the overall system, maximize the output brightness, and the customization of fitting dimensions in a vehicle. Drivers actual responses after using the system will be evaluated. A. LASER Projector The system uses the ESPlus PICO LASER Projector Seeser M2 LASER micro projector as the image source. The red, green, and blue color LASERs are used as the light source, which, after passing through the calibrated lens group, is emitted to MEMS scanning mirror to output the light of each pixel. Its resolution is pixels, the brightness is 15 lumens, and the projection distance and enlargement size are 0.2 ~ 2.4m [8" (20.32cm) ~ 80" (203.2cm)]. B. Virtual System Setting The overall structure of the system includes a LASER micro projector, translucent elements, reflective mirror components, imaging components, and a virtual system opto-mechanical structure. The overall system uses a golf cart as the target carrier of the design, as shown in Figure 3. Figure 3. Golf cart.

3 The folded light path is to accommodate the limited space. The off-axis reflection system [12] is adopted. This system uses a LASER micro projection system as the image source. It must first be imaged via the screen and then used a concave mirror to magnify the image, therfore achieving the design target. The system components include image source, translucent part, concave mirror and semi-transmissive coating part. The optical simulation software ZEMAX is used for virtual image construction. The concave mirror is matched with the semi-transmissive coating part to set the system wavelength, curvature, relative distance, material and tilt angle, and so on. The combiner been made of polycarbonate and the refractive index is The parameters are adjusted to make the system virtual image distance, magnification, size and imaging quality to meet the design requirements and the simulation result structure is shown in Fig. 4. lamented combiner Figure 5. Dual-eyebox simulation. This design is not limited to two eyeboxes; the number of eyeboxes can be increased by superimposing more laminated combiner. More eyeboxes demand higher brightness of the image source. With the advanced light source technology, the development of more eyeboxes is expected. After applying ZEMAX to verify the idea, two eyeboxes are obtained as expected. In this design, the mezzanine has a semi-transflective function on the inner side. The equation of field of view (FOV) as follow: Figure 4. Optics simulation. The LASER micro projector is designed and arranged at 110mm in front of the first semi-transparent part as an image input source. Then the concave mirror magnifies the image and projects it onto the concave semi-transmissive coating part, where the first semi-transparent part is 140 mm from the concave reflective mirror. The semi-transmissive coating distance is 1000mm from the human eye. The human eye s visible range is eyebox size: X direction 90 mm, Y direction 60 mm, the overall opto-mechanical structure has a magnification factor of 4. A 253.0mm virtual image is formed at 2,000mm from the human eye. This design has a mirror, laminated combiner, mirror collocating with laminated combiner to correct aberrations in order to decrease the field curvature and maintain image quality. C. Optical Imaging Quality The conventional combiner is designed to have a same thickness and paralleled inner and outer surface. It is designed to reflect only the system image once, so there is only one eyebox. This design employs semi-translucent and semi-reflective characteristics. When the light passes through the outer reflective surface, an angle is added to the outside. A laminated reflective surface with different reflectivity/ transmittance produces the second eyebox. The second reflector compensates optical properties of the off-axis and concave lenses to ensure image visibility, as shown in Fig. 5 FOV = 2arctan 0.5W (1) D W: width of eyebox D: distance between virtual image to eye By calculations and simulations we can determine the width of eyebox. To avoid two virtual image overlap, so that make viewer feel uncomfortable. We design inner side is tilted by 4.5 degrees. Under the same virtual image path, With 2 eyeboxes, the total eyebox has been raised from 90x60 mm to 90x120 mm. With respect to optical simulation results, the optical imaging quality of this opto-mechanical structure was verified by examining field curvature and distortion values. Fig 6 and 7 shows the field curvature and distortion values, eyebox1 image is 4.04% and eyebox2 image is 4.22%, with a maximum distortion value not exceeding 5%. Fig. 8 and 9 shows the imaging results of the image source and the virtual image. This virtual image is an enlarged virtual image. Figure 6. Field curve of eyebox1 image.

4 industry will be promising. Based on the existing HUD, the eyebox will be increased to enhance the viewer's comfort. Figure 7. Field curve of eyebox2 image. Figure 10. HUD prototype on golf cart. This study successfully enables the HUD to have two eyeboxes. When the driver's body tilt angle is changed, or the driver is operated at a different height, the system does not need to be adjusted, and the convenience and degree of freedom of the driver's posture are improved. Figure 8. Image simulation of eyebox1 image. Figure 11. Virtual image of HUD prototype. Figure 9. Image simulation of eyebox2 image. IV. RESULTS & DISCUSSIONS The optical design focus of the multi-display range optical structure would be its cost, optical size and optical efficiency mode. In addition to having a full range of wide display, the display brightness and distance must be sufficient for the driver to interpret. The HUD technology is gradually being popularized. More and more high-end models are equipped with this system. Other than the original simplified products in the aftermarket, more models of enhanced optical effects have been achieved. In addition to long-distance amplifying virtual images, it is further hoped that the problem of restriction of display area will be solved. Multi-display range HUD is currently more of a foresighted technology, and there are no products available on the market yet, but several prestige international companies continue to invest in this area. With the advanced driver assistance systems (ADAS) issues heating up, and promoted by laws and regulations, it is expected that this The dual-eyebox laminated combiner enables the driver of different heights to read the image under a single HUD system. The core technology is optical design: the optical element design of the laminated combiner for 2 display ranges undergoing design and simulation is set to have 2 eyeboxes which totally equal 90x120 mm, virtual image distance is 2,000mm, the magnification is about 4x, and Distortion has a maximum value of 4.22%. The actual measurement result is that the two eyeboxes are mm and the virtual image distance is 2,000 mm, which are the targeted specifications. Table 1 is a comparison of dual-eyebox HUD and similar product specifications. TABLE I. HUD SPECIFICATION Dual-eyebox Similar product Virtual image distance 2.0m 2.0m Virtual image size Eyebox 90*120mm 90*60mm Combiner Size 330*110*5mm 330*110*2.5mm It is not necessary to adjust the angle of the combiner to obtain multiple viewing angles and different eyeboxes that makes it more convenient to use and the angle does not need

5 to be adjusted during driving, which greatly increases traffic safety. The technologies developed are in line with the market and key fundamental technologies have been established. In the future, technical improvements can be made in response to the demand for commercialization, which would strengthen the marketing position and competitiveness of products, and create a new generation of multi-display range head-up display system. V. CONCLUSIONS As people pay more attention to vehicle safety, various ADAS functions are the main focus of recent development of the vehicle industry. While HUD is an ideal display platform, combining with the functions of the ADAS, the safety factor of driving is highly increased. Prestige automotive manufacturers have also begun to display conceptual sample products, which are expected to be mounted on vehicles in the future. HUD does not just simply display information on the vehicle signal, navigation, etc., but also presents various safety functions, which augments reality to the driver. This feature is important in the future development of vehicle safety. The fundamentals of the HUD technology are stable, and the multi-display range requirements of the corresponding ADAS are currently the focus of development. This study successfully designed the optical design of a HUD system with two eyeboxes using laminated combiner, allowing the driver to be more comfortable with reading the information and keeping a comfortable posture, which is great aid to the improvement of driving safety. For the HUD system, the technical level established in this study is to overcome the aberration problem and increase the eyebox through the virtual image display optical design technology, analysis of human visual characteristics, technology of optical simulation analysis, and allows comfort for the human eye. Currently, prototypes have been built and loaded on golf carts and used with other on-board safety systems to display relevant warning information support platforms so that the driver can be reminded of possible dangerous situations and the safety of driving can be improved. This technology can be combined with other functions of advanced driving assistance system. Using the virtual image projection marking system as the display platform, while combining with various safety-warning functions, can increase the safety of driving. It can help develop diverse functions to strengthen the security of the entire system. It can also assist domestic companies establish key technologies, which strengthen the overall system functions, and meet the needs of the international market, while enhancing product attractiveness and the potential of technological development. REFERENCES [1] Kazumitsu Shinohara, Psychological issues on visual attention while using head-up display, Special Interest Group on Computer GRAPHics and Interactive Techniques Asia Head-Up Displays and their Applications 2015, pp. 3 5, [2] Liu Xia, Regulatory Requirements for Certification of Head-Up-Displays with an Emphasis on Human Factors, Procedia Engineering, Vol.17, pp , 2011 [3] J. Alejandro Betancur, Physical Variable Analysis Involved in Head-Up Display Systems Applied to Automobiles, Augmented Reality - Some Emerging Application Areas, Chapter 13, pp , 2011 [4] J. A. Betancur, J. Villa-Espinal, G. Osorio-Gomez, S. Cu ellar, and D. Su arez, Research topics and implementation trends on automotive head-up display systems, Int. J. Interactive Des. Manuf., pp. 1 16, [5] G. Pettitt, J. Ferri, and J. Thompson, 47.1: Invited paper: practical application of TI DLPR technology in the next generation head-up display system, Soc. Inf. Display Symp. Dig. Tech. Papers, vol. 46, no. 1, pp , [6] G. E. Freeman, Windshield for head-up display system, U.S. Patent , Sep. 22, [7] Y. Tanahashi, O. Kasono, T. Yanagisawa, T. Nomoto, I. Kikuchi, and T. Ezuka, Development of Full-Color Laser Head-Up Display, PIONEER R&D, Vol.22, pp. 4, 2013 [8] Y. Takaki et al., Super multi-view windshield display for long-distance image information presentation, Opt. Exp., vol. 19, no. 2, pp , [9] W. W. Yang, C. H. Chen, and K. T. Luo, 72.2: Compact and high efficiency head-up display for vehicle application, Soc. Inf. Display Symp. Dig. Tech. Papers, vol. 43, no. 1, pp , [10] C.-C. Lee, S.-H. Tsai, C.-C. Kuo, C.-H. Chen, L.-M. Teng, and K.-T. Luo, P-93: Free ghost image and high transmittance optical thin film beam splitter for head-up display, Soc. Inf. Display Symp. Dig. Tech. Papers, vol. 42, no. 1, pp , [11] Andrew Yeh Ching Nee, Augmented Reality - Some Emerging Application Areas, ch.13, pp , [12] B.-H. Kim and S.-C. Park, Optical system design for a head-up display using aberration analysis of an off-axis two-mirror system, J. Opt. Soc. Korea, vol. 20, no. 4, pp , 2016.