Haptics is a relatively underexplored feedback modality in driving, as today’s cars mostly use visual and auditory cues when sending notifications to the driver. Haptics has the ability to communicate information quickly and intuitively, especially if it can tap into a reflex, without putting further load on the already heavily used visual and auditory sensory channels. The increasing autonomous functionality and advanced driver assistance systems of today's cars, as well as the loss of traditional road feel as vehicle mechanical components continue to be replaced by electrical systems, make increased driver-vehicle communication through haptic feedback an important area to explore.
In particular, lateral skin stretch is a promising form of haptic feedback because it conveys magnitude and direction information, creating a rich, analog haptic signal. Possible applications include:
- Safety systems such as collision avoidance, lane keeping, blind spot detection, and low traction warnings
- Navigation and trajectory planning
- Previews of autonomous car actions
- Driver training for trucks and heavy equipment
Skin Stretch Steering Wheel Display
A skin stretch steering wheel display prototype was built by embedding a large thin section bearing into a steering wheel rim.
The display produces lateral skin stretch in the driver's palms and possibly thumb pads depending on the grip, communicating direction and magnitude.
Actuation is provided by a small DC motor and lead screw mechanism.
A right-hand drive Jeep Wrangler was instrumented with the skin stretch steering wheel for testing on the road to produce a realistic haptic driving environment to run experiments in.
The haptic cues tested have been directional pulses that quickly give an intuitive sense of a left or right stimulus to the driver.
As skin stretch feedback is analog, a wide variety of other stimuli are possible.
Validation of On-Road Effectiveness of Skin Stretch Cues
On-road experiments were performed to determine the displacement and speed required to be felt in the car over road vibrations and noise. The direction identification accuracy data are given below, and show that stimuli of 2.5 mm and 4 mm/s are easily perceptible.
Subjects were able to distinguish between four different stimuli (a small and a large version of both the left and right directional pulses) reasonably well, showing that the magnitude of the stimulus is also useful information in the driving context.
The minimum threshold that could be detected in the car was found (0.26 mm for 2 mm/s pulses).
Comparing Skin Stretch and Audio Cues with Driver Distraction
Skin stretch navigation cues were compared to audio while the driver was distracted by a secondary task (auditory N-back) simulating the cognitive and auditory loads of a phone call in an on-road experiment. Skin stretch was found to produce higher turn accuracy as well as be less distracting (better performance in N-back task).
Ploch, C.J., Bae, J.H., Ploch, C.C., Ju, W., Cutkosky, M.R., "Comparing Haptic and Audio Navigation Cues on the Road for Distracted Drivers with a Skin Stretch Steering Wheel," In proceedings of the 2017 IEEE World Haptics Conference (WHC 2017). Best Poster Paper Finalist, Best Poster Presentation Finalist. (preprint).
Ploch, C.J., Bae, J.H., Ju, W., Cutkosky, M.R., "Haptic Skin Stretch on a Steering Wheel for Displaying Preview Information in Autonomous Cars,", In Proc. IEEE/RSJ International Conference on Intelligent Robots and Systems, Daejeon, Korea, Oct 9-14, 2016. Highlight Presentation.