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Range Sensing by Multiple-Frequency Acoustic Phase Detection

IP.com Disclosure Number: IPCOM000061510D
Original Publication Date: 1986-Aug-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 83K

Publishing Venue

IBM

Related People

Bjorklund, GC: AUTHOR [+3]

Abstract

A closed-loop real-time sensor for monitoring and controlling the position of a robot arm or the like is disclosed. A broadband microphone or other acoustic generator 1, mounted on a robot arm 2, is excited by a succession of a suitable number, for example, three different electrical oscillation frequencies f1, f2 and f3 from a multiple frequency generator 3. This produces a succession of three different acoustic oscillations which propagate towards a spatially fixed acoustic detector 4. The output of detector 4 is fed to three lock-in amplifiers 5a, 5b, 5c tuned to frequencies f1, f2 and f3, respectively. The quantities to be measured are the phase-angles /1, /2 and /3, respectively, of the signal with respect to the electrical oscillations.

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Range Sensing by Multiple-Frequency Acoustic Phase Detection

A closed-loop real-time sensor for monitoring and controlling the position of a robot arm or the like is disclosed. A broadband microphone or other acoustic generator 1, mounted on a robot arm 2, is excited by a succession of a suitable number, for example, three different electrical oscillation frequencies f1, f2 and f3 from a multiple frequency generator 3. This produces a succession of three different acoustic oscillations which propagate towards a spatially fixed acoustic detector 4. The output of detector 4 is fed to three lock-in amplifiers 5a, 5b, 5c tuned to frequencies f1, f2 and f3, respectively. The quantities to be measured are the phase-angles /1, /2 and /3, respectively, of the signal with respect to the electrical oscillations. The propagation distance x and the phase-angle / (in degrees) is related by the equation x = (/ / 360) g + m g (1) where g is the acoustic wavelength in the air and m is an (unknown) integer which is the same as the number of integral wavelengths in the path-length x. For a single frequency measurement, m is in general unknown (without doing any fringe counting) and hence x cannot be found. Measurements of / for a suitable number of different frequencies can bypass this problem and provide a highly accurate value for x. A numerical example for this multiple frequency acoustic phase detection technique in air for a case of three suitable frequencies is shown in Table 1. Assuming that the phase angles / can be measured to an accuracy of 1OE, the...