Study on design of vehicle body attitude control using mass transfer mechanism in parallel two-wheel vehicle with underslung vehicle body

In recent years, two-wheeled inverted pendulum vehicles realizing high mobility have been developed. In such vehicles, an inverted pendulum control system maintains the vehicle’s stability by only using the two driving parallel wheels. Therefore, the gravity center of the vehicle body with a passenger is higher than the wheel axis, and the vehicle is moved by leaning the vehicle body forward or backward by moving the gravity center. However, in the case that the vehicle is in the power-off or control-off status caused by a breakdown in the vehicle, the stability of the vehicle cannot be maintained. The inherent mechanical instability of the inverted pendulum vehicle is inimical to safety. Consequently, the vehicle should be modified to provide stable support when the power supply stops or when the passenger gets on and off the vehicle. Moreover, we are now considering such the vehicle that the passengers focused on not only young people but else elderly and handicapped people can drive with sitting attitude. Then, in this case, since the gravity center is lower than the standing posture, the larger action of the passenger’s upper body is required for operating the vehicle. However, the elderly or handicapped passenger is difficult to behave the large action in the vehicle. This paper presents an advanced parallel two-wheel vehicle that has an underslung vehicle body. In the proposed parallel two-wheel vehicle, since large wheels which its diameter is 1.05[m] are applied, and the battery, the actuators and the controller are placed at the lower position in the vehicle body, the gravity center of vehicle body with a passenger can be assigned at the lower position than the wheel axis. Therefore, the vehicle has a pendular structure that enables the vehicle body with the passenger to always maintain the stable posture, even if the vehicle is in the power-off or control-off condition. A 2-DOF joystick that has operation in pitching and yawing is applied to the proposed vehicle. The elderly or handicapped passenger can operate easily and intuitively the vehicle by this joystick. Then, when the passenger sits on the seat of the vehicle, the vehicle body is leaned by moving the gravity center of the vehicle body with the passenger. For compensating the vehicle body leaning, the seat positioning control system is proposed in this paper. The vehicle body’s static posture lean control can be compensated by the proposed control system. Furthermore, the proposed control system is able to change the angle of the vehicle body in a state of stopping the vehicle. In the control system, the control input to the servomotor system is generated by PID control, consisting of