Three-Dimensional Position-Measurement System for Indoor Flying Robot that Uses Ultrasonic Harmonic Waves

It is necessary for an autonomous flying robot to measure its position with high accuracy in order to know its position and speed. A previous study confirmed that, in principle, a position-measurement system improved the resolution by using ultrasonic harmonics during a flying robot's indoor flight. However, the position-measurement system was difficult to use because harmonic waves are weak and unstable compared to fundamental waves. Therefore, this paper proposes two methods of addressing such problems. The first is to improve the detection of harmonics by increasing the nonlinear component of an ultrasonic wave in space. The second is to introduce a control circuit that detects the harmonic components of an ultrasonic wave input to an ultrasonic receiver. The paper first examines ultrasonic behaviors in three-dimensional (3D) space under various conditions and shows the feasibility of applying the nonlinearity of ultrasonic waves to a position-measurement system. Then, based on this, the paper proposes a system for measuring 3D position and attitude using ultrasonic harmonics. Finally, the paper describes several experimental measurements showing that the resolution is improved and the dynamic measurement is realized in 3D space.