Communications: electrical – External condition vehicle-mounted indicator or alarm – Transmitter in one vehicle only
Patent
1996-08-14
1997-11-18
Hofsass, Jeffery
Communications: electrical
External condition vehicle-mounted indicator or alarm
Transmitter in one vehicle only
340903, 340943, 340435, 367 87, 367 98, 367909, 364461, G08G 100
Patent
active
056892500
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The invention relates to an ultrasound process and apparatus for detecting obstacles, such as is used, for example, for driverless vehicles which move in lanes of an automated storage system. By means of the process, the vehicles can detect obstacles in the lanes, such as persons situated there, and can stop in time. In such devices, distinguishing between obstacle-caused ultrasound echoes and ultrasound-frequency interference signals can be problematic.
A process of this type is described in European Patent Document EP 0 326 623 A1. In the process described there periodic ultrasound pulses are emitted simultaneously by two transmitters which are situated side by side, and any ultrasound echo which is reflected by an existing obstacle is detected by receivers arranged at the site of the transmitters. The received echo is analyzed in such a manner that the coordinates of an obstacle in the emission direction as well as transversely thereto can be determined from the echo time. In this case, more than two ultrasound transmitters may be provided which will then, in each case, be controlled in pairs for sequentially generating the pulses. Each original pulse may contain one or several interlaced frequencies; and, in addition, the transmitter frequencies may be varied from one scan to the next by way of software algorithms in order to avoid a failure to recognize an obstacle which reflects ultrasound waves of a specific frequency with a phase shift in the proximity of .pi..
An object of the invention is to provide an ultrasound obstacle detecting process of the initially mentioned type by means of which obstacles can be very reliably detected, even if ultrasound-frequency interference signals are present.
This problem is solved by the process according to the invention, in which the respective echogram sensed after each ultrasound pulse emission is subjected to an envelope curve evaluation during which previous measuring cycles are taken into account. For this purpose, amplitudes which are also found at an isochronous point in preceding echograms are intensified while amplitudes which occur only sporadically in successive echograms are attenuated. This technique makes advantageous use of the fact that, in contrast to an actual obstacle echo, spurious echoes (for example, of reflecting surfaces in a marginal area of the actual ultrasound levels or of industrial noise sources) for a specific measuring duration, do not remain coherent with respect to the emitted ultrasound pulses. By means of the evaluation according to the invention, such uncorrelated spurious echoes are suppressed, while the coherent obstacle echoes are intensified, which considerably improves differentiation between spurious echoes and obstacle echoes. From the "analysis echograms" obtained in this manner, an obstacle can be very reliably detected and its position can be determined with high precision relative to the location of the ultrasound transmitter and receiver. In particular, tests have shown that persons wearing clothing having comparatively weak ultrasound reflection characteristics (and who therefore can otherwise be detected by means of ultrasound only with difficulty), can be very reliably recognized as obstacles by means of this method.
A preferred embodiment of the process according to the invention utilizes an advantageous evaluation method in which newly appearing echo envelope curves are taken into account only when a given amplitude threshold value is exceeded, and the amplitudes of the previous analysis echogram are reduced by a given factor when the amplitude of a corresponding subsequently measured isochronous echogram no longer reaches the given threshold value. As a result, within relatively few measuring cycles, coherent obstacle echoes are considerably intensified relative to the incoherent spurious echoes, even if, in the case of an individual measurement, the latter have higher amplitudes than the obstacle echoes.
In a further embodiment of the invention, the areas of the echo
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"Experiments with a Mobile Robot Operating in a Chuttered Unknown Environment," T. Skewis et al., IEEE, May 1992, pp. 1482-1487.
International Search Report dated Feb. 2, 1996.
Edwards, Jr. Timothy
Hofsass Jeffery
Mayser GmbH & Co., Inc.
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