Communications – electrical: acoustic wave systems and devices – Echo systems – Distance or direction finding
Patent
1995-09-05
1996-12-24
Lobo, Ian J.
Communications, electrical: acoustic wave systems and devices
Echo systems
Distance or direction finding
367908, G01S 1500, G01S 752, G01F 2328
Patent
active
055879691
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to ultrasonic distance sensors based on the pulse-echo process with increased measurement certainty and improved suppression of interfering echo signals. Significant areas of application are non-contact distance measurement for the positioning of workpieces, collision protection or filling-level metrology.
2. Description of the Prior Art
Ultrasonic sensors are known which determine the distance between the sensor and a sound-reflecting object by measuring the transit time of a sound signal from the sensor to the object and back. In this case, the echo is usually detected in that the exceeding of a prescribed threshold value in the received signal is evaluated. This process for distance measurement usually evaluates the transit time of the first detected echo. Any possibly following echoes from other objects situated within the detection range of the sensor are not, in contrast, further processed. By means of time-window control according to Magori, V.; Walker, H.: Ultrasonic presence Sensors with wide range and high local resolution. IEEE Trans. Ultrasonics, Feroelectrics and Frequency Control, UFFC-34, No. 2, Mar. 1987, p. 202-211, the permissible detection range for echo signals can in this case be varied in the desired manner. In this manner, echoes from objects at differing distances from the sensor can also be detected, in that the evaluation time window is cyclically displaced over the measurement range; in this case, the resolution of the individual echoes and the total duration of measurement increase as the length of the time window decreases.
Processes for the processing of ultrasonic echo signals are moreover known in which the received signal is digitally sampled and stored in a memory; in this case, the received signal can also be the demodulated envelope curve of the echoes (European Application 0 459 336). The signal processing takes place following the recording of the received signal by extraction of the echoes by means of a suitable process, e.g. matched filter+threshold value detection. In this manner, all echoes occurring within one measurement can be detected.
Further, in the process which is described in Advances in Instrumentation and Control, Vol. 46, part 2, 1991, Research Triangle Park, NC, US, Duncan: "Ultrasonics in Solids Level Measurements", pages 1355-1366, the emitted and subsequently received ultrasonic signal is digitized by means of a microprocessor and stored as an envelope curve. The process relates to the measurement of the filling level of a container., To determine the useful echo, the echo profile of the empty container is compared with the echo profile of the filled container. Furthermore, it is possible to recognize the useful echo in that a priori knowledge of the nature of the filling material situated in the container and the echo characteristic thereof are used for the recognition of the useful echo.
Furthermore, processes for the suppression of undesired echoes contained in the received signal, for example due to interfering objects which, in addition to the measured object, are situated within the detection range of the sensor, are known. If the interfering objects are spatially fixed and at the same time the range of movement of the measured object is restricted, then an adequate suppression of interfering echoes can be achieved by appropriate selection of the evaluation time window.
Furthermore, it is known that interfering object echoes can be suppressed in that, in a learning phase in which the measured object is not situated within the pickup range of the sensor, in the first instance all interfering object echoes are detected and filed in a memory (German OS 33 37 690). During the measurement operation, the currently detected echoes are compared with the learned echoes. In the event of an adequate concordance, the echo is classified as an interfering object echo and appropriately suppressed, while the remaining echoes are associated with measured objects.
In German OS 33 37 69
REFERENCES:
patent: 4380807 (1983-04-01), Reynard
patent: 4821569 (1989-04-01), Soltz
patent: 4972386 (1990-11-01), Lau
patent: 4992998 (1991-02-01), Woodward
patent: 5060205 (1991-10-01), Phelan
patent: 5157639 (1992-10-01), Leszczynski
"Ultrasonics in Solids Level Measurement," Duncan, Advances in Instrumentation and Control, vol. 46, Part 2, (1991), pp. 1355-1366.
"Ultrasonic Presence Sensors with Wide Range and High Local Resolution," Magori et al., IEEE Trans. on Ultrason., Ferroelec., and Freq. Cont., vol. UFFC-34, No. 2, Mar. 1987, pp. 202-211.
Eccardt Peter-Christian
Kroemer Nils
Magori Valentin
Vossiek Martin
Lobo Ian J.
Siemens Aktiengesellschaft
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