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.