Experimental study of automatic braking properties using an ultrasonic sensor for inverted pendulum vehicles (Proposal of the safety system by using the TTC as the indicator)

Abstract

Inverted pendulum vehicles controlled by movement of driver's center of gravity (COG), such as Winglet or Segway are the examples of Personal Mobility Vehicles (PMV). PMV is sometimes expected to be used in pedestrian spaces. When a driver brakes an inverted pendulum vehicle suddenly, the driver has to move his/her COG backward largely and has the risk to lose his/her balance due to the characteristics of vehicle control. Therefore, we aim to achieve a vehicle control system that is friendly to drivers in emergency. In the previous study, the coupling model of a vehicle and a human had been built on Multibody Dynamics and the technique to brake an inverted pendulum vehicle automatically had been proposed using that model. In this study, we carried out two experiments to decide the timing of the automatic braking system defined as Time To Collision (TTC). We carried out two experiments about stopping distance when a driver brakes an inverted pendulum vehicle suddenly and when the automatic braking system is operated, and we compared those results. Then, it was shown that stopping distance operated by the automatic braking system is shorter than by human driver's sudden braking operations. In addition, we derived TTC₁ ( 0.7 s ) of inverted pendulum vehicles from these experiments about stopping distance by human drivers' sudden braking. Then, we derived reaction time ( 0.4 s ). Finally, we proposed a safety system using TTC₁ and the reaction time. When TTC reaches 1.1[s], the alarm makes a human brake an inverted pendulum vehicle suddenly. Then if a human doesn't brake an inverted pendulum vehicle suddenly and TTC reaches 0.7[s], the automatic braking is operated.