Data processing: measuring – calibrating – or testing – Measurement system – Orientation or position
Reexamination Certificate
2003-05-19
2004-11-16
Pretlow, Demetrius R. (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system
Orientation or position
Reexamination Certificate
active
06820030
ABSTRACT:
BACKGROUND OF THE INVENTION
The current invention relates to a method and a device for determining an angle of rotation or a path.
SUMMARY OF THE INVENTION
In various applications, particularly in devices intended to aid in determining the angular position of a rotatable shaft, it is desirable to know the precise angular position of the shaft. This requirement can be fulfilled, for example, with the aid of analog angle sensors, for example potentiometers, which after being turned on, immediately output the current angular position value in the form of a voltage in every position.
If devices of this kind are used for angular measurement of angular ranges greater than 360°, the problem arises that it is no longer possible to determine which rotation the shaft is currently in. In order to evaluate angular ranges that are greater than 360°, however, incremental measuring transmitters can be used, in which the angular position is determined through forward and backward counting of pulses.
Such incremental measuring transmitters, however, cannot execute absolute angle measurement because it is only possible to count increments that have passed by a receiver.
In some technical measuring tasks, the use of incremental measuring transmitters generates phase measurement values; the values that are actually to be measured, such as an angle, a path, or a distance, must be determined from these phase measurement values. In order to increase the range of unambiguity (corresponding to a phase range from 0-2&pgr;) it is possible to use at least one other measurement conduit with a different phase slope and to derive a greater unambiguity range from a suitable combination of measurement values.
Examples of this include distance measurement using RADAR or modulated laser light. In these instances, N measurements are executed at different frequencies f
1
, . . . f
N
. At the reception point, the signals reflected from a target at a distance x have the following phase shifts (c=the speed of light):
α
i
=
2
·
π
·
f
i
·
2
·
x
c
The phase shifts are thus proportional to the value that is to be measured and proportional to the frequency used. However, the actual measurement values of the phases always lie in the range from 0 to 2&pgr;, i.e. are always determined, with the sole exception of integral multiples of 2&pgr;.
Another example that should be mentioned is an optical angular sensor. In this case, a scan of N optical line gratings is executed, where N tracks with optical line gratings are placed on a disk or a cylinder. There are n
i
periods or lines in one rotation. If the phase positions of the tracks are measured in relation to a fixed measurement window with the aid of optoelectronic detectors, this yields the following phase lengths:
&agr;
i
=(
n
i
·&phgr;) modulo (2&pgr;).
The phases are thus proportional to the rotation angle &phgr; and the periodicities. Here, too, the actual measurement values of the phases always lie in the range from 0 to 2&pgr;.
Finally, multiple wave interferometry should also be mentioned. Here, too, for example paths x are measured through the use of at least two different light wavelengths &lgr;
i
, which yields an increased unambiguity range of
Λ
=
λ
2
·
λ
1
λ
2
-
λ
1
.
Here, too, an appropriate dimensioning yields a phase path of the kind indicated above.
The evaluation of the signals obtained with methods of this kind, i.e. the determination of x and &phgr;, is carried out using vernier methods.
In the classic vernier method, the difference is calculated between two phase signals, where for the case in which this difference is less than zero, 2&pgr; is added. This method has significant limitations since measurement errors in the phases have full impact on the end result. Furthermore, a method of this kind functions only if the two periodicities under consideration differ by precisely 1.
DE-OS 195 06 938 has disclosed a modified vernier method in which the value of a variable to be measured is determined from two phase signals through weighted addition and through the further addition of an angle range-dependent constant. This method excels in its capacity for significantly reducing measurement errors in the phase signals. For this method, too, however, it is necessary that the two periodicities under consideration differ by precisely 1.
Finally, DE-P 1004260 has disclosed a method for determining a rotation angle or distance through the evaluation of phase measurement values. In this method, the phase values that are measured in an N-dimensional space are mapped as N−1 new signals S
i
by means of a linear transformation A. These signals S
i
are transformed with the aid of a quantizing mechanism into corresponding integral values W
i
and are converted by means of a linear mapping C into N real values Z
i
. Weighted phase measurement values &agr;
i
modulo 2&pgr; are added to these values, yielding N estimates for the angle &pgr; to be measured. The N estimates are corrected if need be at their discontinuity points and are added up in a weighted fashion taking their phase angles into account.
The object of the invention is to supply, through the simplest means possible, measurement values for distances x and angles &phgr; on the basis of at least two phase measurement values. It should as a result no longer be necessary to abide by the requirement in the conventional method that the two periodicities must differ by precisely 1.
The invention provides for a particularly simple method, which can reliably determine measurement values that are to be determined, e.g. an angle &phgr; or a path or distance x. By contrast with conventional methods, there is a large degree of freedom in the selection of periodicities for the determination of at least two phase signals. The weighting of the individual measurement values or estimates in the manner that is provided according to the invention has turned out to be particularly easy to execute, computationally speaking.
According to a first embodiment of the method according to the invention, for the case in which two phase values &agr;
1
, &agr;
2
are supplied, the working value k, which is used in the process of determining a rotation angle or a path, is calculated by rounding the term:
[
α
1
·
n
2
-
α
2
·
n
1
2
·
π
]
.
In this case, two phase values &agr;
1
, &agr;
2
are evaluated, which are respectively obtained from sensors or measuring transmitters that each have n
1
and n
2
periods. Computationally speaking, it is easy to carry out the generation and use of such a working value based on two phase values. In this instance, the rounding is the replacement of the calculated value with the nearest smaller or larger whole number. The deviation of the calculated term from the nearest whole number is a measure of the achievable precision of the method.
A scaling relation between the periodicities n
1
, n
2
is suitably selected to be an equation with the form
k
2
·n
1
−k
1
·n
2
=1
Of the infinite number of solution pairs k
1
, k
2
, the one with the smallest numerical values is advantageously used.
According to a particularly preferable embodiment of the method according to the invention, the at least two scaled estimates are calculated in the form
Φ
s
i
2
·
π
=
α
i
2
·
π
+
k
·
k
i
n
i
,
where i=1, 2 . . . N, and k=the working value.
It is also preferable that the weighted summation of the at least two scaled estimates for obtaining a determined estimate &PHgr;
meas
be carried out in the form
Φ
meas
2
·
π
=
∑
i
=
1
N
[
Φ
s
i
2
·
π
·
g
i
]
mod
(
1
)
where the g
i
's (i=1, 2 . . . N) represent the weighting factors for which &Sgr;g
i
=1.
The calculated sum must be taken as modulo 1 (i.e. only the number of decimals need be taken into consideration). It turns out that the resul
Marx Klaus
Steinlechner Siegbert
Wenzler Axel
Pretlow Demetrius R.
Striker Michael J.
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