隨著自動駕駛技術研發的不斷細化，如何解決“暈車”問題，也成為工程師需要研究的課題之一。高仿真級別的汽車模擬器可以協助身處其中的“駕駛員”體驗真車中的各種感受，包括暈車。為了保證自動駕駛汽車的乘客不再遭遇“快停車，我暈的不行了”的困境，如何克服“暈車”，已經變得至關重要。
Ansible Motion是一家位于英國的模擬器專家公司。公司技術聯絡經理Phil Morse援引密歇根大學的近期研究結果稱，在某些特定情況下，比例高達31%的成人均可能在自動駕駛汽車中感到不適。
“其他研究預測中的結果甚至更高，”Morse表示，“英國考文垂大學就曾指出，自動駕駛汽車中的暈車問題‘無法回避’。”
簡單來說，一旦車上人員的視線離開道路，就可能會發生暈車，比如讀取短信、使用筆記本電腦、觀看視頻或玩游戲等。但現在的問題是，在自動駕駛汽車的行程中，上述這些行為都將非常常見，就連駕駛員也不會再一直盯著路面。
你有模擬器應激綜合征（SAS）嗎？
總體來說，影響乘客是否暈車的因素有很多，從設計方面包括車輛的道路顛簸傳輸頻率；噪聲、振動和舒適性（NVH）特性；以及具體車型的視野大小等。未來，由于自動駕駛汽車的乘客無需再繼續關注車輛操作或周邊環境，一些前排乘客甚至還會在高速路段背向車輛行駛方向乘坐，因此暈車問題可能會更加嚴重。
Morse解釋說，“從本質上講，暈車主要是因為人的眼睛與前庭系統的感知出現差異，也就是說人眼可能已經看到了運動，但前庭系統仍并未感受到這種運動，此時就會出現感知差異，反之亦然。”作為一家汽車模擬器專家公司，Ansible Motion正是在這種背景之下推出了一款DIL汽車模擬器。
Morse表示，公司在DIL模擬器的研發中，投入了大量精力進行虛擬試駕，并最終決定將從機器響應、圖像和駕駛員反饋系統入手緩解暈車問題。他說，“目前，汽車廠商已經開始逐步利用模擬器技術，全方位對抗暈車問題。”
為了在駕乘和操控體驗之間做出最佳平衡，汽車設計師和工程師做出了巨大的努力。有時，車輛懸架太松或太緊也會導致暈車的發生，特別是在一些體積較大或車身防翻滾性能不佳的車型中。此外，車輛空調性能不佳、座椅結構問題也有可能加重乘客的暈車癥狀。
與多軸航空模擬器中的宇航員一樣，汽車模擬器內的駕駛員也有可能受到模擬器應激綜合征（SAS）的困擾。Morse表示，“只要駕駛員接收到的環境反饋出現任何的不一致或延遲，就有可能出現暈車。”考文垂大學發現，高達50%的實驗參與者均曾因SAS綜合征的困擾而退出測試。”
正因為如此，Ansible Motion公司希望利用自身對SAS綜合征的了解與相關經驗，解決真實駕駛環境中的暈車問題。比如，公司的工程師可通過調整模擬器設置，專門緩解車內人員的暈車問題，并借此探索車內人員在不同活動下的暈車敏感度及之間的聯系。盡管這項測試尚不為大眾所知，但對測試結果的分析與理解一定可以給未來的車輛設計提供很多有用信息。
“另辟蹊徑”
Morse解釋說，隨著SAE 3級半自動駕駛汽車及SAE 4級、5級全自動駕駛汽車的出現，駕駛員和乘客之間的身份界限已經開始逐漸模糊，這可能會讓暈車成為一個更普遍的問題。考文垂大學的研究人員指出，在非自動駕駛汽車中，大約66%的人曾發生過暈車，且車內娛樂系統也會加重車上人員的暈車問題。
公司的DIL模擬器可提供一個參數可控的獨特測試環境，研究人員輕點鼠標即可輕松控制周邊環境、天氣、車輛性能（物理行為和人體工程元素）及傳感器反饋等多個參數，保證測試的可重復性。
設計師可通過嘗試不斷更換虛擬和實體組件，找到緩解暈車的最佳配置組合。但這種通過改換參數來精確調整駕乘人員體驗的方式，仍不夠直接。
Morse表示，“即使是將圖像延遲控制在一個相對可以接受的范圍也需要非常復雜的硬件和軟件支持。”目前最復雜的挑戰是運動控制。Morse指出，實驗室環境并不一定能夠復制，或按比例反映真實世界中各種力的相互作用。
為了解決這個問題，Ansible Motion選擇了“另辟蹊徑”。據了解，AnsibleMotion的DIL系統以一款精心開發人類前庭系統模型為中心，搭配多個“業內獨有”的運動控制系統，經過專門設計可模擬大腦對運動、空間及方向等非線性參數的感知。
DIL模擬器系統包含一部可提供6個自由度（6DOF，指剛性物體可在三維空間自由運動的軸數）的分層運動機，并將模擬艙安置在精確控制促動器的頂層上，從而簡化了對促動器的要求。
分層運動機的下層提供平面運動，而上層裝置則用于產生俯仰、側傾、前行等運動。正因這種設計，DIL模擬器的重心比一般的六足模擬器（常見于航空領域）更低。
Morse表示，“模擬器的主軸均由單促動器控制。在這種設計下，各種力的控制更加輕松，線性表現更好，且慣性也低的多，非常適合敏感的汽車物理模型。”據了解，Ansible Motion有3家F1客戶，該系統最初也是為賽車運動設計的，因此對方向和穩定度的要求非常高，哪怕是進行最細微的調整，也必須向駕駛員提供最準確的反饋。
Corum Technology是一家專攻底盤動態與感知測試的公司。該公司汽車動力學部主管Tim Roebuck對Ansible Motion的系統進行了采樣處理。Roebuck指出，用戶可隨時調整模擬器的物理和反饋參數，“因此，如果我要評估開車或乘車時的舒適程度變化，以及造成這種變化的原因，這種模擬系統比真車測試快很多，幾乎可以模擬所有可能的情況。”
Roebuck表示，從最“正常”的汽車響應，到各種更加“極端”的情況，都可以利用這款設備進行車內情況的模擬，因此“我可以輕松感覺出任何體驗優化，以及這與車輛行駛狀態之間的關系。”
未來，隨著自動駕駛系統的不斷發展，此類模擬技術與測試手段將在汽車設計中發揮更大價值。
Motion sickness has become a very real issue for engineers developing and testing autonomous vehicle technologies. Automotive simulators can reach such high levels of realism that they may cause their 'drivers' to experience motion sickness similar to that in a real car. Overcoming the issue is vital for ensuring that autonomous vehicle passengers don't suffer the same 'stop the car, I've got to get out' nausea.
Phil Morse, Technical Liaison Manager of Ansible Motion, a U.K.-based simulator specialist, cites a recent University of Michigan study which concluded that in some situations, up to 31% of adults are likely to experience significant discomfort in an autonomous car.
“Other studies predict even higher percentages," Morse noted. "One, by the University of Coventry [U.K.], refers to motion sickness in automated cars as being ‘the elephant in the room.’”
The problem starts with occupants take their eyes off the road. Causes of car-sickness include reading and texting, laptop computer use, watching videos and gaming—each a plausible scenario for occupants (including the “driver”) during an autonomous car journey.
Do you suffer SAS?
Design factors such as the vehicle’s road disturbance transmission frequency; noise, vibration and harshness (NVH) characteristics and, depending on the vehicle, the levels of outward visibility are all likely to influence the onset and severity of car sickness. Now, add the potential that the occupants are focused neither on the ride nor their vehicle's surroundings. Those sitting in the front seats may, in the future, even be turned rearwards during highway stretches.
“Essentially, it occurs as a result of a perceived mismatch between the eyes and the vestibular system—when motion is seen and not felt, or vice versa,” explained Morse, whose company specializes in Driver-in-the-Loop (DIL) simulator systems for vehicle engineering, including motorsport.
He said that because so much time is spent inside simulators conducting virtual test drives, recent trends in engineering-class simulator technologies have been aimed squarely at mitigating driver discomfort via more responsive machinery, graphics and driver feedback systems. "Today, OEMs are turning to the use of these simulator sickness-mitigation technologies as a means of investigating car sickness," he said.
Great attention is paid by vehicle designers and engineers to achieve optimum ride and handling combinations. But too much or too little suspension compliance—soft, under-damped ride quality particularly in large cars and poorly controlled body roll—also conspire to cause motion sickness. Inadequate HVAC performance and non-optimal seat structure design may further compound the problem.
Drivers in vehicle simulators may suffer Simulator Adaptation Syndrome (SAS) just as their aerospace-industry counterparts do in aircraft multi-axis simulators. “Even very small amounts of latency and/or mismatch between the various environmental feedbacks, e.g. motion, video feeds, etc., can lead to problems," Morse explained. The University of Coventry found that 50% of participants dropped out of simulation tests caused by SAS."
Because of this, Ansible Motion is working to counter real-world motion sickness, using its knowledge of and experience with the symptoms. For example, company engineers can induce motion sickness deliberately by tweaking the simulator’s settings, creating a useful path to explore human sensitivities while people are engaged in different tasks inside a car. It's hardly a popular test regimen, but analyzing and understanding these sensitivities are useful for informing the design of production vehicle.
Taking a different approach
Morse explains that as semi-autonomous (SAE Level 3) and fully autonomous vehicle (Levels 4 and 5) capabilities begin to blur the lines that separate the in-car experiences of drivers and passengers, occurrences of car sickness could become more prevalent. The University of Coventry researchers stated that in non-autonomous vehicles about 66% of all people have experienced motion car sickness, and that the use of in-vehicle entertainment systems can increase its incidence.
DIL simulators offer a unique environment for investigating these effects because they provide a repeatable, controlled environment in which the surroundings, weather, the car itself (physical behavior and ergonomic elements) and the sensory feedback delivered to the driver/occupant, can be altered with a few keystrokes.
By swapping real and virtual components around, designers can efficiently study the combinations that work best to mitigate motion sickness. But manipulating driver/occupant experiences with the required degree of precision is far from straightforward.
“Even cutting down on the graphical latency to an acceptable degree requires highly sophisticated hardware and software," Morse said. The most complex challenge is the motion control. Simply attempting to replicate or scale down the real-world forces doesn’t necessarily work in a laboratory environment, he noted.
To tackle this, Ansible Motion uses what it describes as a radically different approach. It is centered on a carefully developed model of the human vestibular system mated to “industry-unique” motion control systems, designed to stimulate the brain’s perception of movement and spatial orientation, which is inherently non-linear.
The technology incorporates a six-degrees-of-freedom (6DOF; the number of axes that a rigid body can freely move in three-dimensional space) stratiform motion machine. This device simplifies the actuation requirements by placing the cabin on top of layers of precision-controlled actuators.
The first stages provide ground-plane cueing, while upper layers generate the pitch, roll and ride motions. This results in a considerably lower center of gravity than hexapod simulators (used by the aerospace industry) would provide.
“Forces are much easier to manage and primary axes are governed by single actuators, which gives it linear control authority with far less inertia – a perfect fit for connectivity to sensitive vehicle physics models," explained Morse. The system was first developed for motorsport applications (Ansible has three F1 customers) where subtle steering and stability cues are crucial in providing the right feedback to highly experienced drivers.
Tim Roebuck, Head of Vehicle Dynamics at Corum Technology, a chassis dynamics and subjective specialist testing company, has sampled the Ansible Motion system. He noted that the simulator's physics and cueing feedback can be altered on the fly, "so assessing changes in my comfort level as I carried out driving and non-driving tasks could happen at a much faster pace than any testing in a real car. Adjustments in the simulator are almost infinite it seems," Roebuck said.
He was able to experience anything from ‘normal’ vehicle driving responses to ‘extreme’ variations, "so it was easy to describe any improvements in how I felt, and how those related to the vehicle tuning states.” Use of such technology and testing methods will become more valuable as the auto industry increases its development of autonomous-driving systems.
Author: Stuart Birch
Source: SAE Automotive Engineering Magazine
Ansible Motion公司的Phil Morse（右）與坐在DIL模擬器中的公司工程師。公司表示，該技術可協助用戶克服暈車，同時適用于常規車型和自動駕駛汽車。
Phil Morse與Ansible Motion的DIL模擬器。
Ansible Motion的DIL模擬器的性能數據圖。
Ansible Motion模擬器可協助用戶在真實環境中克服暈車，特別是在自動駕駛汽車中。
Ansible Motion的工程師正在測試DIL模擬器套裝。
正在搭建中的Ansible Motion模擬器平臺。