Time optimal control of ultrasonic transducers for improved multiple object recognition

Ultrasonic distance sensors are widely used in robotics and automotive applications because of their low cost, robustness and small size. One disadvantage of low frequency piezoelectric transducers operating in air is their small bandwidth. This results in poor spatial resolution when discriminating multiple objects within the directivity of the sensors. One method proposed in the literature is using amplitude modulation. Drawbacks of this method are very long pulse duration and the resulting high effort for matched filtering of the received signals. In order to detect multiple objects, a novel approach is proposed. It is based on time optimal control of the transmitting transducer. The optimal control sequence is determined by quadratic programming. The resulting pulse signal has a considerably shorter decay time compared to a conventional burst excitation. This allows a better resolution for the recognition of objects that are close to each other.