The origin and development of vehicle HUD (head-up display)

HUD (Head Up Display), like many high-tech products, was transferred from the military field to the civilian field. It first appeared on fighter jets in the 1960s as a display system for pilot assistance.

This pilot assisted driving display system can project the aircraft status and important external information required for flight driving, such as aircraft flight parameters, aiming and attack information, etc., onto display devices such as the combined glass in front of the pilot or the pilot's helmet through a projection unit.

The principle is to reflect the image of the optical aiming scale onto the transparent glass plate in front of the pilot's cockpit, then let the transparent glass plate reflect the image light into the pilot's eyes, and finally project a virtual image in front of the pilot through a specific optical system.

As the use of HUD optical systems on aircraft became more and more common, General Motors first integrated HUD technology into automobile research and development in 1988. The initial design concept could only project simple vehicle speed information for the driver to view, but this migrated technology received widespread attention and discussion both inside and outside the industry.

In 2001, Ford began to promote models that can display color information HUD, which greatly satisfied people's visual enjoyment; in 2003, BMW began to sell cars equipped with HUD in the European market; then, in 2006, Cadillac also launched a model with an internally configured HUD that can project colorful and switchable virtual image information; in 2013, Texas Instruments took a new path and began to move towards augmented reality, making more cutting-edge expansion in the field of HUD technology. Subsequently, some high-end car brands at home and abroad have continuously equipped their models with HUD systems.

With the development of the automobile market and the expansion of market demand, the most commonly used HUD types on the market are windshield HUD (W-HUD) and augmented reality HUD (AR-HUD).

The predecessor of W-HUD is combined HUD, namely C-HUD, which is a transitional version of W-HUD. When HUD was first developed, it was considered that the surface shape of the car's front windshield had uncontrollable factors. If it was used as the final reflective display element in the imaging light path, the aberration of the entire system would be difficult to solve. Therefore, a transparent glass plate was placed on the windshield during the design to replace the role of the windshield so that the virtual image would appear on the glass plate. The advantage of this design method is that it reduces the difficulty of optical design; the disadvantage is that the narrow space above the dashboard leads to a smaller area of ​​the transparent glass plate, a very short projection distance, and in the event of a traffic accident, the transparent glass can easily injure the driver or passengers by mistake, and the safety factor is low. Therefore, the C-HUD design was quickly eliminated by the market, and it was replaced by W-HUD.

W-HUD is designed using the car's front windshield as the final projection display element. The car's front windshield reflects the virtual image light into the driver's eyes, thereby displaying virtual image information in front of the car. Due to the different shapes of the front windshields of different models, W-HUD requires a specific optical path design, and the entire system must be integrated into the limited and narrow space inside the car dashboard. To this end, the W-HUD optical path structure design and component selection need to meet the requirements. At present, the optical path structure adopts an off-axis three-reflector type, and the components use free-form reflectors. However, the uniqueness of the windshield surface shape determines that each model of W-HUD must be designed according to the model, and it is the main model currently used in the market.

With the introduction of the concept of augmented reality (AR) technology and the continuous maturity of subsequent technologies, HUD industry-related R&D personnel have proposed new design solutions in the market, that is, the integration of WHUD and augmented reality (AR) technology. The innovative product brought by the combination of the two has many advantages. It can not only display instrument information and navigation information for the driver, but also provide instantaneous change information based on the surrounding environment of the vehicle body. The above information will be projected into the virtual image of the car HUD, thereby escorting the driver's safe driving. This kind of car HUD is called AR-HUD.

The main differences between AR-HUD, C-HUD and W-HUD are as follows: First, it has a larger field of view, so the driver can see a larger projection screen, and the projected information can be richer; second, the imaging distance becomes farther; third, the vehicle condition information and navigation information can be integrated with the real road surface, making the driver feel as if they are personally on the scene. This technology is currently at the forefront of automotive HUD research and development.