Analysis of an ultrasonic spatial locating system

• Published in: IEEE transactions on instrumentation and measurement 1976-03, Vol.IM-25 (1), p.43-50
• Main Authors: Moritz, William E., Shreve, Peter L., Mace, Leslie E.
• Format: Article
• Language: English
• Subjects: Accuracy; Linearity; Microphones; Radiation detectors; Random access memory; Sparks
• ISSN: 0018-9456; 1557-9662
• DOI: 10.1109/TIM.1976.6312303

Two-dimensional systems for locating points in a plane are readily available. X-Y digitizers, light pens and cursor controllers are common examples. However, none of these techniques can be easily extended to locating points in three dimensions. Having such a capability would permit tracking points in space as well as determining the relative position and orientation of multiple-point arrays. An ultrasonic spatial locating system has been assembled and evaluated. Based on the transit time of a shock wave produced by a small electric spark, the position of one or more sparks can be determined with respect to a coordinate system. The coordinate system is formed by 3 linear condenser (electret) microphones arranged orthogonally which detect the arrival of the wave front. A microcomputer is incorporated for system control and for calculating the spatial coordinates (X, Y, Z) from the measured transit times. In addition, the computer can be used to perform certain calibration and performance checks to maintain proper system operation. An analysis of the system indicates that it is possible to locate points within a cube 50 cm on a side with an accuracy of better than ±0.6 mm. The acoustic transit time and the ringing of the microphone determine how many samples per second may be taken. Data rates of about 100 per second are well within the capabilities of the system.