Three-dimensional tracking using qualitative bionic sonar

A sonar-driven robot, ROBAT^3D, has been implemented to track an object moving in three dimensions using qualitative interpretation of the sonar signals. ROBAT^3D is equipped with a sonar system consisting of five identical transducers configured in the form of a cross. The center transducer emits an acoustic pulse and the echoes are detected by pairs of receivers that flank the transmitter horizontally and vertically. The vertically-oriented receivers are used to control the pitch while those oriented horizontally control the yaw. ROBAT^3D is driven by four air jets that provide lateral forces that direct the heading toward the object. Two bits of information are extracted from each emission, one for pitch correction and the other for yaw correction. The correction is determined by which sensor in a pair first detects the echo. That sensor actuates an air valve supplying the contralateral jet to correct the heading. The range to the object can be determined from the echo time-of-flight. This simple nonlinear analog control system is very fast and can track an object that has an angular velocity upto π /2 rad /s. A trade-off exists between the size of a limit cycle oscillation and the bandwith of the system, determined by the thrust of the jets and the delay in the sonar sensing.