Communications – electrical: acoustic wave systems and devices – Distance or direction finding – By combining or comparing signals
Reexamination Certificate
2001-09-05
2003-05-27
Lobo, Ian J. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Distance or direction finding
By combining or comparing signals
C367S120000, C187S391000, C187S394000
Reexamination Certificate
active
06570817
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an apparatus for detecting the position of an object which can move along a predefined path. Such apparatus may be used for controlling the position of a lift cage or the like and thus ensuring its positioning at predetermined stops according to floor levels.
BACKGROUND OF THE INVENTION
European Patent No. 694 792 discloses an apparatus of this type for detecting the position of a movable object which has an acoustic signal waveguide which extends along a travel path and has a predetermined, uniform speed of propagation of sound, and has a signal input coupler which is connected to a signal generator and is located on the movable object to couple an acoustic signal into the acoustic signal waveguide. In this case, signal output couplers are arranged at both ends of the acoustic signal waveguide and are each connected to a counter, the two counters being clocked by a clock generator and connected to a subtracter for the output signals from the two counters. The output signal from the subtracter, as a measure of the propagation—time difference of the acoustic signal coupled in from the point at which it is coupled into the signal output couplers, can be processed by an evaluation unit to form a signal which is representative of the instantaneous position of the movable object on the travel path, the signal input coupler operating with a signal spacing which is greater than the propagation time of sound from one end of the travel path to the other. If the movable object is at a standstill, standing waves can form, depending on the position of the object, as the result of reflections of the acoustic signal at the ends of the acoustic signal waveguide, and can lead to measurement problems as a result of fluctuations in amplitude.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an apparatus for detecting the position of an object which can be moved along a prescribed path, with which it is possible to pick up measured values even when the object is at a standstill.
An apparatus for detecting the position of an object moveable along a predetermined travel path in accordance with the present invention comprises an acoustic signal waveguide extending along the travel path and having a predetermined, uniform speed of propagation of sound; a signal input coupler located on the moveable object to couple a clocked acoustic signal into the acoustic signal waveguide, at least one signal output coupler being arranged at one end of the acoustic signal waveguide and being connected to an evaluation unit for determining the propagation-time of the sound signal from a position at which it is coupled in to the at least one signal output coupler and, for generating a signal representative of the instantaneous position of the moveable object on the travel path, wherein the signal input coupler couples in, as acoustic signal, adjacent pulses having a varying time interval.
By varying the time intervals between successive pulses fed into the acoustic signal waveguide, it is possible to pick up valid measured values even in unfavorable stopping positions of the movable object. Since in this case, the standing wave is shifted as the result of variation of the repetition time, and thus evaluation outside the oscillation nodes of the said wave is made possible.
Further objects, embodiments and advantages of the invention will become apparent from the following description and the claims.
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Apparatus for Detecting Position, Hoepken, 09/490,647, filed Jan. 24, 2000 (12 pg).
Apparatus for Detecting Position, Hoepken, 09/489,953, filed Jan. 24, 2000 (14 pg).
Apparatus for Detecting Position, Turk, 09/490,648, filed Jan. 24, 2000 (12 pg).
K. A. Schmersal GmbH & Co.
Lobo Ian J.
Patterson, Thuente Skaar & Christensen
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