Position and Intensity Sensing of a Large-Area Tactile Sensor for Hands-on Detection in Conditional Autonomous Driving

Hands-on detection (HOD) is critical to making the transition decision on the driving authority between the human driver and the automated system in conditional autonomous vehicles. However, existing HOD solutions using individual sensing elements are limited in area sensing capabilities over the entire steering wheel. To implement both position and intensity sensing, a compliant large-area sensor that is able to cover the entire rim of a steering wheel is developed based on the technique of electrical impedance tomography (EIT) in this work. The sensor is made by spray coating low-cost exfoliated graphite polymer composites over an insulating hyper-elastic fabric, forming a continuous piezoresistive sensing area ( $100\times10$ cm) using only boundary electrodes for measurements. The spatial performance is investigated in both simulation and experiments, showing nonuniform wavy patterns in terms of the reconstructed peak, the reconstructed size, and the position error. To obtain correct information on the tactile intensity, the relation between the reconstructed peak and the size is modeled by an inverse equation, the fit coefficient of which is found an effective indicator to the intensity. Indentation experiments validates the proposed method to estimate the intensity, and the position error is measured 1.1 ± 0.7 cm. The performance for HOD is also evaluated by wrapping the compliant sensor over a true-size steering wheel in laboratory environment, validating the potential of applying the cost-competitive large-area sensing solution for conditional autonomous driving.