Research On Ultrasonic Range-Finding System With Large Sensing Range

Ultrasonic sensors for range-finding are the basis of many robotic and automaticapplications, such as obstacle avoidance and collision waming systems of cars, self-guidedautonomous vehicles, fieldwork robots and so on. However, there is specified restriction when anairborne ultrasonic transducer is used in field operation since its merit of figure Q is higher (thefrequency bandwidth is relative lower), and it is difficult to improve both of the directivity andlarge sensing range of the airborne ultrasonic transducer. Accordingly, it is still, even now, one ofthe challenging problems in ultrasonic field to develop the high performance ultrasonictransducer and the ultrasonic range-finding system in air.An ultrasonic range-finding system consists of an ultrasonic transducer and a transmitting &receiver electronics and a signal processor. The originality of this paper is to lucubrate thefundamentals of the ultrasonic transducer which converts electrical energy to mechanical energy(sound pressure) and reciprocally, mechanical energy to electrical energy, the detectingarithmetic for the weak sound wave signal, and the implementation procedure of the ultrasonicranging system with large measuring stroke. The main topics of this paper include:(1) In order to design and fabricate the miniature ultrasound receiver, we had pursued thestudy on the Cymbal transducer's dynamic properties of both electricity and mechanics. As aresult, the relationship between the radial displacement and the axial displacement of the Cymbaltransducer, as well as the resonance modal were derived theoretically.(2) According to the physical characteristics of the ultrasound wave and the piezoceramicmaterial, as well as the performance of the ultrasonic transducer, the resonating mode andfrequency of a piezoceramic disc oscillator were selected. By application of the acousticimpedance matching technique to the structure of the transducer, and the optimal matchingtechnique of both mechanical and electrical impedances to the transmitted electronics, we hadsuccessfully enlarged the sensing-range and improved the sensing directivity of the transducer,which is capable of checking multi-way noises.(3) It was proposed originally a new composite ultrasonic transducer combined with thedisc transducer and the Cymbal-type receiver to cope with the Doppler Effect.(4) A novel optimal-design method for the push-pull convertor and its related formula for calculating the efficiency of energy-transforming were proposed originally, and the transmittingcircuit implemented by the proposed method has better efficiency of energy converting.Furthermore, the receiving electronics with a novel time-gain control circuit and highsignal-to-noise ratio (SNR) was designed and implemented to experiment with the transducer.(5) By utilizing the fact that the correlation detection is equivalent to the matchingdetection, a necessary modify formula for determining the time-of-flight (ToF) when usingmatching detection method was presented. A novel method was hereby proposed to improve theprocessing gain and real-time response of the range-finding system, that is, to use matchingdetection method based on binary phase-shift keying (2PSK) signal while the ultrasonictransmitted signal is in form of binary amplitude-shift keying (2ASK), and a fast matchingdetection algorithm was implemented by computing the cross-correlation function with two-stepprocedure for ultrasonic range-finding system.Experimental results show that the effective sensing range of the transducer is greater than32 meters, and the width of beam is less than±5°, which has better performance than that of theexisting ones, for instance, the similar products in Airducer Catalog (AIRMAR Tech. Corp,,U. S. A.). The ultrasonic range-finding system developed in this paper has been applied to someother projects, for instance, which have provided one of the solution of field-object-detection forthe key project of "Study on the navigational control theory and methods for mobile robotics inunknown environment" (supported by National Natural Science Foundation of China, authorizedNo. 60234030) and the project of "Unmanned Campaign Platform" (An Advanced ResearchProject of the 10th Five-year Plan, supported by Equipment Headquarters).It is no doubt that all the techniques adopted in this paper can directly be applied to developsonar systems in water with high cost performance.