Electricity: measuring and testing – Electrical speed measuring – Including speed analog electrical signal generator
Reexamination Certificate
1999-10-25
2001-06-05
Oda, Christine (Department: 2862)
Electricity: measuring and testing
Electrical speed measuring
Including speed analog electrical signal generator
C324S207200, C324S207250, C340S672000
Reexamination Certificate
active
06242905
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a method of identifying the direction of rotation of a wheel using Hall probes which are disposed about the circumference of the wheel, via evaluation signals phase-shifted relative to one another.
In a large number of cases, it is desirable to detect not only the position and speed of a rotating wheel, for example a gearwheel, but also the direction of rotation of the wheel. In general, a sensor that is capable of establishing the position, speed and direction of rotation of a wheel is thus sought.
For detecting the position and speed of a gearwheel, there is already a differential dynamic Hall sensor which measures the difference field between two spatially offset Hall probes and gives especially good results if the phase angle between the two signals produced by the two Hall probes is 180°. This is because, in this case, one Hall probe lies over a tooth of the gearwheel, while the other Hall probe lies over a gap between two teeth of the gearwheel. With such a differential dynamic Hall sensor, however, it is not possible to identify the direction of rotation of the gearwheel.
This is because in order to identify the direction of rotation of a gearwheel as well, yet another item of phase information is necessary, and this can be made available by two Hall sensors offset by 90° relative to one another.
German Utility Model DE 89 09 677 U1 discloses a device for identifying rotation in which digital signal sequences are respectively derived from at least three Hall probes by at least two differential Hall ICs. For accurate rotational speed identification, with a view to higher resolution, the frequency of the output signal can be doubled relative to that of only one single differential Hall IC. By phase comparison, it is in principle also possible to identify the direction of rotation.
Published, Non-Prosecuted German Patent Application DE 41 04 902 A1 discloses a method and a configuration for identifying a direction of motion, in particular a direction of rotation. To that end, two signals, phase shifted by 90°, which are derived from two receivers disposed offset in the direction of motion of a signal source, are formed by adding and subtracting the output signals. From the sign of the 90° phase shift between the sum and difference signals, the direction of rotation can be uniquely determined. This method is, however, highly sensitive to DC magnetic fields. There is therefore an offset in the sum signal relative to the difference signal, which is twice as great as the DC magnetic field, with the result that reliable further processing of these signals entails serious difficulties.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for identifying the direction of rotation of a wheel using Hall probes which overcomes the above-mentioned disadvantages of the prior art methods of this general type, which allows reliable identification of the direction of rotation without having to demand exact coordination between the tooth spacing and the Hall probe spacing. In particular, the method is intended to be insensitive to DC magnetic fields.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of identifying a direction of rotation of a wheel, which includes:
disposing Hall probes including a first Hall probe, a second Hall probe and a third Hall probe in succession in a circumferential direction about the wheel, the second Hall probe is disposed between the first Hall probe and the third Hall probe, the first through third Hall probes generating output signals phase-shifted relative to one another;
deriving a first evaluation signal and a second evaluation signal from the output signals of the Hall probes, an output signal of the third Hall probe being subtracted from an output signal of the first Hall probe to obtain the first evaluation signal, and the output signal of the first Hall probe being added to the output signal of the third Hall probe resulting in a summed value and two times an output signal of the second Hall probe being subtracted from the summed value to obtain the second evaluation signal;
sampling one of the first evaluation signal and the second evaluation signal at predetermined sample times resulting in a tested evaluation signal being sampled and the other of the first evaluation signal and the second evaluation signal being a sampling evaluation signal defining the predetermined sample times; and
deriving a trend or sign of the tested evaluation signal being sampled, the trend or sign having a direction of rotation definitively assigned to it with reference to the tested evaluation signal sampled at a respective sample time.
In order to implement the method, a first, a second and a third Hall probe are disposed in such a way that the second Hall probe is positioned between the first and third Hall probes. Two evaluation signals, shifted by 90°, are obtained from the output signals of the first to third Hall probes, there preferably being a change in sign of the second evaluation signal in relation to the first evaluation signal when the direction of rotation changes.
The second Hall probe advantageously lies exactly mid-way between the first and third Hall probes, since the oscillation amplitudes of the evaluation signals are then at a maximum.
The method therefore requires only three Hall probes, which can be fitted in one Hall sensor. Using this sensor, the direction of rotation, for example of a gearwheel, can be determined reliably from a change in a sign of the second evaluation signal.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for identifying the direction of rotation of a wheel using Hall probes, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
REFERENCES:
patent: 5241267 (1993-08-01), Gleixner
patent: 5489844 (1996-02-01), Preston
patent: 8909677 (1990-06-01), None
patent: 4104902A1 (1992-08-01), None
patent: 61-160011 (1986-07-01), None
patent: 5-288763A (1993-11-01), None
patent: 08110348A (1996-04-01), None
Andersen Henry S.
Greenber Laurence A.
Lerner Herbert L.
Oda Christine
Siemens Aktiengesellschaft
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