Active damping of ultrasonic transducers for robotic applications

Ultrasonic ranging in air over short distances offers advantages for robotic applications. Such sensing methods can employ transducers small enough to fit into a robot gripper, thereby providing terminal homing capability. Any such short range time-of-flight systems, however, have to solve the problem of rapid receiver recovery after the transmit pulse. In the present case the problem has been solved by an active damping scheme. The transducer is a capacitive element and is connected across an inductor to form an electrically resonant circuit at the acoustic frequency of interest. The LC tank is in the feedback path of a novel circuit that can be changed continuously from positive to negative feedback conditions. When the feedback is positive oscillations rapidly build up, when negative they just as rapidly die down. At the end of each positive - negative cycle essentially all of both the electrical and mechanical energy has been extracted from the system, which is then ready to receive the echo. In this way ranging is readily achieved down to ∼1", which is adequate for robot gripper applications.