A METHOD FOR ACCURATE DETECTION OF TIME OF ARRIVAL - ANALYSIS AND DESIGN OF AN ULTRASONIC RANGING SYSTEM

Many industrial applications demand accurate ranging operations, for example, robotic end-effector positioning and measurement of vibrations in machine monitoring tasks. For instance, measurement of the position of a robotic end effector in high-accuracy applications demands the following stringent specifications from a ranging system: (1) absolute ranging accuracy of +/- 0.025 mm (+/- 0.001 in.), (2) working range of approximately 2 m (6.56 ft), (3) update rate > 100 Hz, and (4) high reliability. It is shown that an ultrasonic ranging system that meets the above specifications may be feasible. The system model is based on measuring the distance between a transmitter and a receiver. A novel method to detect the instant when the signal arrives at the receiver is described. The method combines envelope peak detection and phase measurement to determine the time of arrival, and it gets close to meeting the accuracy criteria. To verify the analytical predictions, distances of up to 0.9 m were measured using a prototype system. The absolute accuracy of such measurements was +/- 0.150 mm (+/- 0.006 in.). The tests performed indicate that the errors are caused primarily by air turbulence and may be decreased by averaging more samples. In this paper ultrasonic ranging from a transmitter to a receiver in a three-dimensional space setting is addressed.