Data processing: measuring – calibrating – or testing – Calibration or correction system – Position measurement
Reexamination Certificate
2000-04-07
2002-07-09
Hilten, John S. (Department: 2863)
Data processing: measuring, calibrating, or testing
Calibration or correction system
Position measurement
C702S095000, C702S094000
Reexamination Certificate
active
06418388
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an arrangement for offset compensation of two orthogonal sensor signals S(x) and S(y), which are supplied by two sensors (
2
,
3
) and are preferably designed for angle measurements, the offset compensation taking place in dependence on the geometric arrangement of Free pairs of test values P
1
(x
1
, y
1
), P
2
(x
2
, y
2
) and P
3
(x
3
, y
3
) of the sensor signals S(x) and S(y) in a system of coordinates, the center of a circle on which the three pairs of test values P
1
(x
1
, y
1
), P
2
(x
2
, y
2
) and P
3
(x
3
, y
3
) are situated in the system of coordinates having center coordinates &Dgr;x and &Dgr;y relative to die origin of the system of coordinates.
Many known measuring systems determine the test quantity to be measured from two test signals x and y which are mutually orthogonal, i.e. show a mutual phase shift of 90°. The one measuring channel thus generates a test quantity proportional to the sine of the quantity to be ascertained and the other a signal proportional to the cosine of said quantity. Such an arrangement renders possible, for example, the calculation of an angle in angle measurement systems. A change in the value of the signal amplitude is unimportant here as long as this amplitude changes in an identical fashion with temperature or owing to other influences in both channels, Nevertheless, so-called offsets adversely affect the measuring accuracy. These offsets may be regarded as superimposed DC voltage or current signals, which are to be reduced to a minimum. The offset compensation in the manufacture of the sensors is an intricate matter and is avoided. Instead, it is attempted to carry out an offset compensation in the application surroundings.
U.S. Pat. No. 5,297,063 discloses an arrangement for this purpose which carries out an on-line compensation of the offsets in that the center is calculated of a circle on which three test value pairs are situated. This circle center can be calculated from known geometric relations. A disadvantage of this arrangement is that the procedure is comparatively complicated and that a microprocessor is required.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an arrangement with an offset compensation which is as simple as possible.
According to the invention, this object is achieved in that correction means are provided which carry out a sign determination of the values &Dgr;x and &Dgr;y of the center coordinates of the circle on which the three pairs of test values P
1
(x
1
, y
1
), P
2
(x
2
, y
2
) and P
3
(x
3
, y
3
) are situated in a repetitive cycle in each measuring cycle, while in each measuring cycle at least one of the pairs of test values differs from the pair of test values used in the preceding measuring cycle, and which means generate correction signals Kx and Ky with which the sensor signals S(x) and S(y) are complemented, in that the correction means in every measuring cycle increase or decrease the offset correction signal Kx by a correction value KWx compared with the offset correction signal Kx of the previous measuring cycle in dependence on the sign of the center coordinate &Dgr;x , and in that the correction means in every measuring cycle in a similar manner increase or decrease the offset correction signal Ky by a correction value KWy compared with the offset correction signal Ky of the previous measuring cycle in dependence on the sign of the center coordinate &Dgr;y.
The arrangement according to the invention bases its operation on the geometric relationships, i.e. that the three pairs of test values derived from the test signals S(x) and S(y) lie on a circle whose center characterizes the offsets &Dgr;x and &Dgr;y of the two sensor signals S(x) and S(y). The arrangement according to the invention does not carry out an exact calculation of the offsets &Dgr;x and &Dgr;y, so as to keep the expenditure as small as possible. Instead, only the signs of the values of &Dgr;x and &Dgr;y are determined, which is substantially easier to do and which nevertheless allows for a very good correction. This is achieved in that a correction is carried out in each measuring cycle for three pairs of test values each time, so that the amount of correction required for the values &Dgr;x and &Dgr;y becomes smaller at each correction operation and &Dgr;x and &Dgr;y are adjusted to as small values as possible, depending on the chosen step size of the change, whereby an optimized offset compensation is obtained.
Correction means are for this purpose provided in the arrangement which carry out a sign determination of the values of &Dgr;x and &Dgr;y in a cyclical manner. &Dgr;x and &Dgr;y here form the center coordinates of that circle on which the three test value pairs P
1
(x
1
, y
1
), P
2
(x
2
, y
2
) and P
3
(x
3
, y
3
) are situated, which pairs should have been previously determined, and one test value pair at least should be different from the test value pair used in the previous measuring cycle.
The correction means further generate offset correction signals Kx and Ky which are superimposed on the sensor signals S(x) and S(y). The sensor signals S(x) and S(y) are thus corrected by means of the offset correction signals Kx and Ky, so that an offset compensation of these signals is achieved.
This is done in the same manner for the two offset correction signals, but independently of one another. First the said sign of the center coordinate &Dgr;x is thus determined for the purpose of the offset correction signal Kx in each measuring cycle for the three pairs of test value P
1
(x
1
, y
1
), P
2
(x
2
, y
2
) and P
3
(x
3
, y
3
). Depending on this sign, the offset correction signal kx is then increased or decreased by a correction value KWx, depending on the sign which was determined. The offset correction signal Kx starts from that of the preceding cycle, i.e. the offset correction signal Kx is increased or decreased by the correction value KWx in each cycle in dependence on the value of the center coordinate &Dgr;x determined in that cycle. In this manner the offset correction signal Kx is increased or decreased in each cycle such that the value of the center coordinate &Dgr;x decreases continually and approaches a minimum, the value of which depends on the value of the chosen correction value KWx. This is an iterative process in which an offset compensation takes place in several measuring steps, i.e. several measuring cycle periods, which process is close to optimal and nevertheless requires very little expenditure, because a determination of the sign of the values of &Dgr;x is sufficient.
The procedure for obtaining the offset compensation for the signal S(y) corresponds to the procedure described with reference to the sensor signal S(x); however, the offset compensation for both signals is carried out mutually independently.
The change in the value of the offset correction signal Kx by the correction value KWx applied in each cycle may advantageously be inexpensively provided by means of two integrators. The integrators then merely receive a signal in each cycle indicating whether a change in the offset correction signals by an upward correction value or by a downward correction value is to be applied, whereupon the previously integrated values forming the offset correction signals of the previous cycle are increased or decreased by the new correction value.
The correction values KWx and KWy may have programmable levels, as is provided for in a further embodiment of the invention as defined in claim
3
. The value may then be differently programmed, for example, in dependence on the field of application.
If the correction values KWx and KWy have the same value in every cycle, then a correction of the offset compensation can only be applied by that value in each cycle. If a faster offset compensation is desired or required in certain cases, it is advantageous not to choose the values of KWx and KWy to be constant but to make them dependent on the sign found for the two center coordinates &Dgr;x and &Dgr;y in the previous cycle and on
Biren Steven R.
Hilten John S.
Koninklijke Philips Electronics , N.V.
Washburn Douglas N
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