Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Distributive type parameters
Reexamination Certificate
2002-05-29
2004-07-20
Le, N. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Distributive type parameters
Reexamination Certificate
active
06765393
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method and to a device for determining the distance to an object.
In this connection, the measuring principle of the stimulation and evaluation of a sympathetic vibration is used: a transmitter transmits a modulated signal, in particular a modulated light signal, along a measured length in the direction of the object. The signal reflected by the object along the measured length or along a part thereof is detected by a receiver and delivered—directly or via further components—to a filter module with defined phase frequency characteristics. The output signal of the filter module is in turn delivered—directly or indirectly—to the transmitter.
A resonant circuit is formed in this manner by the transmitter, by the measured length, by the receiver, by the filter component and, optionally, by further components. The transmitter is integrated in this resonant circuit such that its modulation frequency corresponds to the frequency of resonance of the resonant circuit dependent on the signal transit time over the measured length. The sought distance to the object can thus be calculated by a measurement of the frequency of resonance of the resonant circuit. The prerequisite for the functioning of this measurement principle is the use of a filter module whose phase response for the desired measurement range ensures the occurrence of a resonant condition, that is, the production of a phase shift of a total of 2&pgr; or of 360° or of an integral multiple thereof.
SUMMARY OF THE INVENTION
It is an underlying object of the invention to increase the accuracy of the distance determination for this known measurement principle.
Embodiments of the present invention provide a plurality of phase frequency characteristics, which differ with respect to phase and amount, used to form the resonant circuit and to determine the corresponding frequency of resonance. A comparison value is available by this taking into account of at least one further phase frequency characteristic which can be used in the manner explained in the following to check the determined distance and/or to increase the measurement accuracy.
The frequencies of resonance determined for the different phase frequency characteristics are preferably taken into account for the determination of the sought distance. For this purpose, the different frequencies of resonance—or the respective distances corresponding to these frequencies of resonance—are put in relation to one another. It is in any case important for the results of a plurality of measurements of the frequency of resonance for different phase frequency characteristics to be not further processed independently of one another, but to be combined with one another for the evaluation.
The evaluation of the measured frequencies of resonance is therefore not restricted to the purpose of an exclusive and direct distance determination. The frequencies of resonance determined for the different phase frequency characteristics can in particular be additionally used for an non-ambiguity check, i.e. for a check as to which of the possible resonant conditions is present. The phase information to be evaluated namely repeats for different scanning distances with a certain periodicity. With the known measurement principle, this can result in an incorrect determination of the sought distance under unfavorable conditions, that is, when the correct resonant condition was not used as the basis for the evaluation of the measured frequency of resonance.
In contrast to this, a check can be made in embodiments of the invention due to the taking into account of different phase frequency characteristics as to which integral multiple of 2&pgr; or of 360° is present. An extension of the range of non-ambiguity is thereby achieved.
A possible procedure for this non-ambiguity check comprises comparing the frequencies of resonance determined for the different phase frequency characteristics with one another or with at least one reference value, or of determining and comparing with one another a plurality of different phase frequency characteristics and in particular also distances corresponding to different resonant conditions. It is of advantage for such a comparison evaluation if the underlying distance of the object is unchanged or if any change in distance in the meantime is known and taken into account as well.
Alternatively or in addition to this non-ambiguity check, the measurement accuracy can be increased in that the different phase frequency characteristics, or the frequencies of resonance determined from these, are used to determine the parasitic phase shift, that is, that phase shift which is caused by components other than by the filter component explained.
As already explained, the resonant circuit can include further components, for example an amplifier, a band pass filter or a phase correction circuit. These components can change their contribution to the phase shift along the resonant circuit, for example due to temperature effects or aging effects, in a manner which cannot be predicted with sufficient accuracy by one-time reference measurements. Inaccuracies in the distance determination result if the portion of the measured phase shift which is due to the signal development along the actual measured length is no longer trackable.
To compensate for such errors and for further systematic errors, the plurality of frequencies of resonance corresponding to the different phase frequency characteristics can be used to determine the parasitic phase shift. This determination of the parasitic phase shift can take place individually for each distance measurement or the result can be compared with earlier results. To obtain the highest possible accuracy here, the distance of the object should remain as unchanged as possible, or any possibly known change in distance should also be taken into account, during the measurement of the different frequencies of resonance.
At least the different phase frequency characteristics, which correspond to the determined frequencies of resonance, and a suitable resonant condition can be taken into account for the explained determination of the parasitic phase shift.
An evaluation unit can be provided within the apparatus for the carrying out of the explained non-ambiguity check and/or for the explained determination of the parasitic phase shift.
The different phase frequency characteristics can differ with respect to their respective center frequency and/or to their gradient in the region of their different or same center frequency. It is, however, preferred for the transmission areas corresponding to the different phase frequency characteristics and respectively restricted by the 3 dB limit frequencies to overlap.
It is furthermore preferred if the phase shift caused by the phase frequency characteristic of the filter component dominates over the parasitic phase shift in the area of frequency of resonance of interest for the distance determination, in particular with the center frequency. The phase shift effected by the filter component can in particular be at least one and a half times larger than or twice as large as the parasitic phase shift.
It is furthermore of advantage if at least one phase frequency characteristic used for the determination of the distance is selected such that the corresponding frequency of resonance lies in a frequency range within which the frequency of resonance can be determined with particularly high measurement accuracy. The further frequencies of resonance can be selected such that the further evaluations, for example the non-ambiguity check or the determination of the parasitic phase shift, can take place particularly simply or with a particularly high accuracy.
As explained, it is of advantage if the different frequencies of resonance are determined for the respective same distance of the object. It is preferred for this purpose if the frequencies of resonance of the resonant circuit are determined simultaneously or at least at short time intervals to one another.
The constructional e
Pastor Sebastian
Pierenkemper Hans-Werner
He Amy
Le N.
Sick AG
Townsend and Townsend / and Crew LLP
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