Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
1998-07-28
2001-01-16
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
Reexamination Certificate
active
06173614
ABSTRACT:
TECHNICAL FIELD
The invention relates to a method of measuring the height of the cutting table of an earth processing implement, such as an agricultural implement, relative to a surface of the ground with crops by means of an acoustic transducer arrangement.
BACKGROUND ART
German Offenlegungsschrift No. 4,324,766 discloses a measuring of the height of a cutting table of for instance a combine harvester by means of ultrasound. This known measuring method is encumbered with the draw-back that possible crops on the surface of the ground can cause undesired reflections and attenuation, which to a considerable degree makes the measuring difficult.
BRIEF DESCRIPTION OF THE INVENTION
The object of the invention is to provide a method of measuring the height of a cutting table by means of a sound signal, where the method is not encumbered with the above draw-backs.
A method of the above type is according to the invention characterised in that the sound signal emitted by the transducer arrangement is of a particular character or follows a particular pattern and is preferably a pseudonoise signal covering a predetermined frequency band, said sound signal being compared with the reflected signal in such a manner that said signals are mutually delayed until the comparison has reached an optimum, whereafter the delay represents a measurement of the distance to the surface of the ground.
This comparing technique involves only a measurement of the signals deriving from the reflection from the surface of the ground, whereby it is utilized that the signals received present a pattern identical with the pattern of the transmitted signals. In this manner the picking up of even weak signals has been facilitated, whether these signals are weak or not compared to interference signals.
According to the invention it is possible, if desired, to perform a mathematical filtration of the pseudonoise signal.
The pseudonoise signal can furthermore according to the invention be weighted so as to achieve a uniform energy density across the desired bandwidth.
According to a particularly advantageous embodiment of the invention an array of optionally phase-controlled transducers is used as transmitters. As a result, it is furthermore possible to utilize the data found in the phases for achieving a more accurate measuring of the height than hitherto known.
As an alternative, it is possible to use an array of acoustic transducers as receivers.
According to a particularly advantageous embodiment of the invention the comparison is performed by the correlation coefficient being measured between the signals to be compared, said signals being mutually delayed until said correlation coefficient has reached its maximum.
Moreover, it is according to the invention possible to perform a simultaneous measuring between a transmitter and a plurality of receivers, said measuring signals being analyzed individually before they are evaluated and combined so as to provide the final measuring result. In this manner it is possible to compensate for one or more irrelevant elements, such as stones, interfering with one or more of the transmission paths.
Finally, it is according to the invention possible to alternate between various pseudonoise signals.
The invention relates also to a device for carrying out the method according to the invention for measuring the height of the cutting table of an agricultural implement relative to a surface of the ground with crops by means of an acoustic transducer or a transducer arrangement. The sound signal emitted by the transducer or the transducer arrangement presents according to the invention a characteristic pattern which can be easily distinguished from irrelevant signals. The resulting measuring device is particularly simple.
REFERENCES:
patent: 4738137 (1988-04-01), Sugg et al.
patent: 4910717 (1990-03-01), Terry
patent: 5060205 (1991-10-01), Phelan
patent: 5155983 (1992-10-01), Sheehan et al.
patent: 5365442 (1994-11-01), Schmidt
patent: 5714687 (1998-02-01), Dunegan
patent: 0 511 768 A2 (1992-04-01), None
Hald Jens Arne
Langkjær Carsten
Darby & Darby
Dronningborg Industries A/S
Miller Rose M.
Williams Hezron
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