Communications – electrical: acoustic wave systems and devices – Echo systems – Distance or direction finding
Patent
1993-12-06
1995-05-23
Pihulic, Daniel T.
Communications, electrical: acoustic wave systems and devices
Echo systems
Distance or direction finding
G01S 1532, G01B 1700
Patent
active
054187583
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a distance measurement system. More particularly, it relates to apparatus and a method for signal processing ultrasonic signals to determine the distance between and displacement of two points in space.
BACKGROUND ART
In various situations it is necessary to measure distances unobtrusively between two points (i.e. there must be no physical members connecting the points), or to measure changes in distances between the two points. It is often necessary for these measurements to be fully automated and to be made continuously or at regular intervals. One particular example where regular unobtrusive distance and displacement measurements are required, is in the underground mining industry. Underground mine shafts are prone to collapse, resulting in significant losses in productivity and possibly lives. Usually collapses of underground shafts are preceded by the convergence of the shaft roof and floor. By detecting this convergence, it is possible to predict impending shaft collapses, and thus allows mining operators to attempt to avoid a possible disaster.
It is preferable that such a divergence detection system should have a high degree of accuracy, reliability and repeatability under conditions which are adverse while being unobtrusive and easily transportable. Existing measurement systems include extensiometers, wire-wound potentiometers and laser interferometers.
Extensiometers and wire-wound potentiometers suffer from a number of limitations. They rely on an obtrusive measurement technique resulting in errors due to mechanical disturbances arising from the general nature of mining operations. They are often used only as temporary apparatus and have limited resolution. For these reasons they cannot be used in many areas where convergence measurements are required. Laser interferometry suffers from the fact that a relatively clean environment is necessary for correct operation. The environment within a mine is in direct conflict with this requirement. Furthermore, its cost make laser systems very undesirable.
The present invention attempts to overcome one or more of the above disadvantages with the use of ultrasonic waves, ultrasound. Ultrasound is comprised of travelling longitudinal mechanical waves at frequencies above those audible to the human ear, normally above twenty kilohertz. When travelling through air, the waves may be described in terms of the variation of air pressure at a particular point. The pressure varies with simple harmonic motion, firstly above and then below the average atmospheric pressure at that point. The reflection of ultrasonic waves from a plain surface is similar to the reflection of light from a non-ideal mirror. That is, the angle of reflection is approximately equal to the angle of incidence. This is especially true at high frequencies. However, as the frequencies decrease, more defraction and dispersion take place.
Distance between and displacement of two points in space can be measured using ultrasound measurements. By comparing distance measurements at different points in time, it is possible to detect relative movement between the points in space. In order to measure the distance between the points, an ultrasonic toneburst can be projected from one of the points using an ultrasonic transducer, the toneburst is reflected by a suitable reflector at the second point and the toneburst then returns to the point of transmission. The transit time of the pulse is proportional to the total distance travelled. It is critical to accurately measure the time between the transmission and reception of the toneburst, in order to provide an accurate measurement of the distance between the two points.
In order to complete the distance measurement it is necessary to have knowledge of the speed of the ultrasonic waves in air. This speed may vary depending on temperature, air pressure, moisture content, etc. If it is known that the speed of sound does not change in the application of the UDMS, then a constant value for the speed of
REFERENCES:
patent: 3458853 (1969-07-01), Daniels et al.
patent: 4313183 (1982-01-01), Saylors
patent: 4543649 (1985-09-01), Head et al.
patent: 4630226 (1986-12-01), Tanaka
patent: 4677599 (1987-06-01), Obayashi et al.
patent: 4831604 (1989-05-01), McKnight et al.
patent: 4933915 (1990-06-01), Bostrom
Connell Wagner (Old) Pty. Ltd.
Pihulic Daniel T.
Stowell Harold L.
University of Technology Sydney
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