Closed-Loop Posture Control of Parallel Biwheel Vehicle Driven with Stepping Motor

Abstract

A simple motion control scheme of a dynamical system driven with a stepping motor is proposed. The scheme is examined through posture control of a parallel biwheel vehicle that consists of an inverted pendulum supported by two coaxial parallel wheels. Posture of the vehicle is regulated by state feedback where a step rate of the stepping motor instead of a motor torque is used as control input to the system. The proposed scheme can produce steady vehicle motion around an unstable equilibrium position by numerical simulation. The simulated initial responses reveal that there is an appropriate range of peak static torque values of the stepping motor. A large peak static torque results in the increase of vibrational amplitude of the vehicle around the unstable equilibrium position, and a small torque causes step failure due to overload before appearance of unrecoverable tumbling motion. In experiments, the posture of the vehicle can be regulated within an inclination angle of ±5×10^-3 rad under the proposed scheme with a 5-phase 500 step/rev stepping motor. An optical rotary encoder of 1.75×10^-3 rad/pulse resolution is used as the inclination angular sensor.