The Design of a Vibrotactile Seat for Conveying Take-Over Requests in Automated Driving

Abstract

The driver of a conditionally automated car is not required to permanently monitor the outside environment, but needs to take over control whenever the automation issues a "request to intervene" (i.e., takeover request). If the driver misses the takeover request or does not respond in a timely and correct manner, a takeover could result in a safety-critical scenario. Traditionally, warnings in vehicles are conveyed by visual and auditory displays, though recently it has been argued that vibrotactile stimuli could also be a viable approach to present a takeover request to the driver. In this paper, we present a vibrotactile seat designed to convey dynamic vibration patterns to the driver. The seat incorporates 48 vibration motors (eccentric mass rotation) that can be individually controlled. One 6 × 4 matrix, with an average inter-motor distance of approximately 4 cm, is located in the seat back and one in the seat bottom. The DC-voltage to the motors is controlled by three Pulse Width Modulation (PWM) drivers, which in turn are controlled by an Arduino microcontroller. A study with 12 participants was conducted to investigate (1) at which vibration intensity participants find a vibratory stimulus annoying and whether this threshold changes over time, (2) how well participants are able to discriminate vibratory stimuli as a function of spatial separation, and (3) which of six dynamic vibration patterns are regarded as most satisfying. Results showed that participants' annoyance threshold reduced when they were repeatedly exposed to vibrotactile stimuli. Second, the percentage of correct responses in the two-point discrimination test increased significantly with increasing inter-stimuli distance (i.e., from 4 to 20 cm). Third, participants seemed to be more satisfied when more motors were activated simultaneously (i.e., more spatial overlap). Overall, the results suggest that participants are well able to perceive vibrotractile stimuli in the driver seat. However, the results suggest that repetitive exposure to vibrotactile stimuli may evoke annoyance, a finding that should be taken into account in future designs of vibrotactile displays. Future studies should investigate the possibility to convey complex messages via the vibration seat.

Rolling Out the Red (and Green) Carpet: Supporting Driver Decision Making in Automation-to-Manual Transitions

“…For a review, see [13] and [25]). Auditory and vibrotactile TORs have been shown to elicit faster reaction times than visual ones [26]. These effects may be due to the fact that auditory and vibrotactile feedback compete less for perceptual resources than visual feedback [27] as driving is primarily a visual task [28].…”

Driver response times to auditory, visual, and tactile take-over requests: A simulator study with 101 participants

“…The loudness of the beeps was 80.6 dB (measured with the BAPPU-evo from ELK). A vibrating seat as previously used in [17] provided the tactile take-over request. Forty-eight motors located in the seat bottom and back vibrated twice at approximately 60 Hz for a duration of 240 ms (100 ms inter-stimulus interval).…”

Dimensional Evolution of Intelligent Cars Human-Machine Interface considering Take-Over Performance and Drivers’ Perception on Urban Roads

“…As a research hotspot in the field of transportation, automated driving can greatly improve driving safety and alleviate modern traffic problems such as accidents, fuel emissions, and road congestion [7][8][9]. Meanwhile, it can promote driving comfort and reduce the impact of the environment [10]. When the automated driving system is out of order or is unable to deal with the traffic conditions, the driver needs to control the vehicle manually so that driving safety can be ensured.…”