Research on HMI Design of Automated Driving Assistance System

Author | CDylan, System Architect

Produced by | Automotive Electronics and Software

The so-called automatic driving assistance is an intelligent driving system that requires the driver and the intelligent driving system to jointly complete the "target and event detection and response". The intelligent driving assistance system relies on human-computer interaction technology to realize information exchange and command transmission with the driver. It can be said that the relationship between the intelligent driving assistance system and the human-computer interaction system is very close. The goal of the HMI (Human Machine Interface) system design is to enable the driver to interact with the vehicle more conveniently and efficiently, thereby improving the driving experience of intelligent driving and enhancing driving safety.

HMI information is interactive information transmitted to the driver through display screens, dashboards or other interactive systems (visual, audio, tactile, etc.). It includes:

1.1、Notification

Notification refers to various reminders or message notifications sent by the HMI system to the driver. These notifications include text pop-ups (sometimes accompanied by icons) or voice. Specifically, notifications related to automatic driving assistance in the HMI system include the following categories:

• Function status reminder: such as function cancellation, function degradation, reminding the driver to activate the function when conditions are met, system failure, etc.

• Safe driving reminder: If the vehicle ahead drives away, remind the driver to continue running ACC, remind the driver to take over, remind the driver to drive carefully if the road ahead is complex, collision reminder, door opening collision warning, etc.

• System operation feedback: For example, the ICA system self-check feedback function cannot be activated when activated by the user.

Figure 1: Notification diagram

1.2.Te lltale Icon

Telltale refers to an indicator light that communicates specific vehicle status or warning information to the driver. These telltales are usually displayed in the form of icons on the vehicle's dashboard or HUD to help the driver quickly understand and process vehicle-related information.

Specifically, Telltales involving automated driving assistance systems include the following:

• AEB Telltale , including AEB function off, AEB brake activation alarm, and AEB function malfunction indicator light;

• ICA Telltale , including portrait and landscape control status indicators;

• RCW Telltale , rear collision risk indicator;

• LCC Telltale , a lane departure warning indicator;

• FCTA/RCTA Telltale , forward side collision, rear side collision risk indicator light;

• DOW Telltale , collision risk indicator when opening the door.

Figure 2: Schematic diagram of car instrument Telltale

1.3 Animation

Animation refers to the display content that the HMI system uses real-time animation based on the information output by the intelligent driving assistance system. It includes lane lines, surrounding obstacles, surrounding vehicles, the vehicle and its status (such as lateral deviation, too close to the curb), and driving events (such as collision risk animation). In the case of an HD map, it can combine the map information to depict richer content.

Figure 3: Animation diagram of intelligent driving instrument

1.4、Audio Chime

Chime refers to a prompt or warning sound, which is usually designed as a short sound segment to convey specific information or warnings to the driver to enhance the driver's attention to the vehicle status and environment. Chime sounds usually respond simultaneously with Notification, Telltale or driving events.

1.5. Voice prompt

Voice prompts are functions that provide information and instructions to the driver through voice interaction. These voice prompts are usually generated and played by the vehicle's voice recognition system, and are designed to allow the driver to interact with the vehicle through voice without having to divert attention to observe the display or operate the control panel.

Voice prompts can be responded to simultaneously with Notification, Telltale, or driving events, or they can be interacted with separately. When voice prompts and notifications respond to the same trigger condition, the text design of voice prompts and notifications is different. Notifications are usually short texts that convey information to drivers in concise and concise language to reduce the time the driver focuses on the screen and ensure driving safety.

1.6. Setting User Settings

The Setting item refers to the status feedback of various ADAS function switches and intelligent driving assistance systems.

Figure 4: Schematic diagram of intelligent driving function settings

According to the operating environment conditions of the automatic driving assistance system and based on the urgency of human-computer interaction, we can divide the human-computer interaction information of the intelligent driving assistance system into the following four categories, from low to high urgency.

2.1 Message

Messages are text, images, and sounds that are delivered to the driver via the display, dashboard, or audio system. These messages are intended to help the driver better understand the vehicle status, environmental conditions, or system operation. These messages are low priority for the driver and can be paid attention to. If not paid attention to, it will not affect normal driving.

Its interactive forms can include driving assistance animations, Telltale displays of normal functional status, and text notifications/voices, etc.

2.2. Attention

When the operating conditions of intelligent driving change and these changes have affected the normal operation of the system, "Attention" is intended to remind the driver to maintain driving attention to ensure safe driving and effective vehicle operation. To ensure that the driver pays attention to this information, in addition to the interaction methods mentioned in "Message", the driver can be reminded through voice prompts, vibration, visual, etc.

Specific scenarios include driver distraction reminders, driver hands-off reminders (early stage), etc.

2.3 Warning

Warnings can be divided into medium-level warnings (Caution) and high-level warnings (Warning) according to the situation.

• "Caution" usually refers to a medium-level warning message, which is used to inform the driver that there may be potential problems or risks in the system status or driving situation. These messages are not as urgent or serious as emergency warnings, but the driver still needs to pay attention and take some measures or adjust his driving behavior.

  
  

  "Caution" scenarios include sensor failure, reminders that the system will exit, etc.

  
  

• "Warning" usually refers to a higher level warning message, which is used to inform the driver that there are serious problems or potential safety risks in the system or driving. These messages require the driver's immediate attention and immediate action to avoid potential danger or damage.

  
  

  “Warning” scenarios include warnings of impending collisions.

It should be noted that when some trigger conditions occur, the urgency of the driver's attention increases with the duration of time, and the information level will change dynamically. For example, when the driver takes his hands off the car, the information level may be "Attention" for a certain period of time at the beginning (such as 10 seconds), and may rise to "Caution" as the hands-off continues.

3.1 General Principles

HMI design as a whole needs to comply with the principles of trust and efficiency:

1. Improve users’ trust in automated driving assistance systems

research shows:

• In general interaction scenarios, users trust the intelligent driving assistance system more when the tone is gentle and tactful than when the tone is direct, while in warning interaction scenarios, the opposite is true;

• Although users with different personality traits perceive the design features of human-computer interaction differently, and users have stereotypes about different design features, it ultimately does not affect the change in trust emotions.

2. Principles for improving human-computer communication efficiency

From the perspective of driver cognition, poor communication between humans and machines is the main reason why drivers reduce their trust in automatic driving assistance systems. Through HMI design, drivers can understand the behavior and intentions of the system, clarify the respective responsibilities of humans and machines in various situations, and improve drivers' driving trust.

Regarding the human-computer communication method for conveying information to the driver, based on message classification, when designing the HMI system, we can adopt diverse and multimodal human-computer interaction methods according to different scenarios to achieve the goal of improving the efficiency of human-computer communication.

3.2. Design criteria determined by combining HMI elements

1. Principle of unity

The design of elements should be consistent throughout the system, including the style, size, lines, and layout of icons. The color, size, and style of icons representing the same status between different functions should be consistent. In this way, the driver can maintain a consistent user experience and understanding no matter which function he uses or which information he views. For example, the Telltale representing the horizontal and vertical working status of ICA needs to be the same color, such as green; the Telltale representing AEB failure and LDW failure also needs to be the same color, such as red.

Figure 5: FEB/LDW Telltale Diagram

The design of the automatic driving assistance system involved in the Audio Chime must also consider unique and unified rules. It must have clear recognition and be distinguishable from the Chime sounds of other systems. For example, the Chime sound of the infotainment system and the Chime sound of ADAS must be different. Some special designs can be considered in terms of frequency, duty cycle, and sound volume.

2. Principle of Significance

The layout of the HMI interface (animation, notification), the use of icons, and the selection of text should clearly convey information and functions so that the driver can quickly and accurately understand and operate the system.

Elements should be designed to be intuitive and easy to understand, so that the driver can directly understand and anticipate the function and effect of each element.

3. Usability principle

HMI element design should be able to be accumulated as design assets, which is conducive to its extension in other projects. It not only improves product development efficiency internally, but also reduces the learning cost for customers.

In addition to the instrument display content, the Setting items also need to consider the principle of ease of use to improve operating efficiency, reduce user learning costs, and increase user usability and user experience. The design can be carried out by setting a reasonable initial state and centralizing and intensively setting various ADAS function settings.

Setting items should be able to provide timely feedback to users to confirm that their operations have been received and understood by the system.

4. Priority strategy

When the trigger conditions of multiple intelligent driving assistance systems are triggered at the same time, especially for Notifications with the same display area, it is necessary to set an information arbitration strategy based on the priority of the information and design the minimum display time to ensure that users can read the information they need.

5. Timing strategy

For multimodal interactions, responses must be given at the same time, and the time consistency and real-time nature of multimodal interactions must be ensured.

4.1. Voice Selection

When determining the gender of the voice agent, it is important to consider that the general stereotype of users is that communication with men is more reliable and communication with women is more emotional. When using a male voice as an agent for intelligent driving assistance, the gender characteristics of the agent coincide with people's stereotypes, which is more conducive to users' trust in the automatic driving assistance system and increases their evaluation of the system's ease of use and usefulness.

4.2. Voice, Tone and Text Selection

Choose different tones according to the needs of the scenario. In general interaction scenarios, it is recommended to use a gentle tone to interact to promote users' emotions towards the intelligent driving assistance system. In warning interaction scenarios, it is recommended to use direct tone and short text to interact to increase trust in the system.

• For example, when the driving assistance system is actively changing lanes, you can say "There is enough space ahead, your vehicle is ready to accelerate and change lanes". Through transparent information and gentle voice interaction, it promotes the user's emotional feeling for the system and enhances the user's trust in the intelligent driving assistance system.

• For example, when the user needs to actively control the vehicle, the system can directly express the need for the driver to manually drive immediately by saying “Please take over the vehicle immediately, the driving assistance function will be exited”, thus arousing the user’s awareness of vigilance.

5.1. Light strip

Light strips play an increasingly important role in HMI, delivering key vehicle information and warnings to drivers in a visual way to improve human-computer interaction efficiency, ensure driving safety, and provide drivers with an immersive driving experience.

1. The current headlights include:

• Instrument breathing light

Figure 6: Diagram of instrument breathing light

• Steering wheel light strip

Figure 7: Schematic diagram of the steering wheel light strip

5.2、3D Chime

1. The concept of 3D Chime was proposed in 2020, but because 3D Chime involves functional definition and information output status in the field of intelligent driving, audio channel design, speaker layout, sound and image positioning in the cockpit, etc., the current results are not satisfactory and there is still a lot of room for improvement.

   
   

2. 3D Chime's innovation can start from sound frequency and sound image, and design sounds that can quickly attract the driver's attention and allow the driver to associate accurate information.

references:

1. Zhan Qinfang. Research on the design of intelligent driving central control system based on human-machine trust[D]. Guangdong University of Technology, 2023.

2. MUIR B M. Trust in automation: Part I. Theoretical issues in the study of trust and human intervention in automated systems[J]. Ergonomics, 1994,37(11): 1905-1922.

3. You Fang, Zhang Jinghui, Zhang Jun, et al. Trust-based takeover system interaction design in smart cars[J]. Packaging Engineering, 2021.

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