Electricity: measuring and testing – Magnetic – Displacement
Patent
1998-02-09
2000-10-10
Patidar, Jay
Electricity: measuring and testing
Magnetic
Displacement
32420725, G01B 714, G01B 730
Patent
active
061305359
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a measuring device for the contactless determination of a rotary angle. A measuring device is known form FR-OS 90 15 223, wherein a stator and a rotor are moved in relation to each other. There is a narrow air gap between the stator, which respectively is made of a magnetically conducting material, and the rotor. A first ring-shaped permanent magnet is arranged over a length of 180.degree. in the rotor and is radially polarized. A second ring-shaped. permanent magnet of opposite polarization is located in the remaining area of the stator, also amounting to 180.degree.. The stator furthermore has two air gaps located diametrically opposite each other. A Hall sensor is arranged in at least one of these air gaps. The strength of the magnetic field extending through the Hall sensor changes with a rotary movement of the rotor in relation to the stator. But the linear measuring range of the measuring signal generated in this manner is limited to .+-.75.degree.. This linear measuring range furthermore has a change of the sign. It would be possible in an elaborate manner to remove this sign change with the aid of an electrical circuit.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a measuring device for contactless determination of rotary angle, in which an additional magnet is arranged in a magnetic field of the at least one ring magnet and has a magnetic flux extending through an element which is sensitive to a magnetic field and providing a parallel displacement of a measuring curve.
The measuring device in accordance with the invention for the contactless determination of a rotary angle has the advantage, that a linear measuring range of more than .+-.110.degree. is possible, without a sign change in the measuring voltage occurring in the linear measuring range. This sign change-free linear measuring range is possible in both directions of rotation of the measuring device, that is in a positive or negative direction of rotation. By means of this, two linear measuring ranges are also obtained. With the aid of the additional magnets it is possible in a simple manner to achieve a sign change-free linear measuring range by the vertical displacement of the measurement curve. The vertical displacement of the measurement curve can be controlled in a simple manner by means of the strength and the polarization direction of the additional magnet. The direction of displacement is a function of the direction of magnetization of the additional magnet. The created magnetic bias of the magnetic field-sensitive element, and thus the displacement of the measurement curve, is independent of the angle of rotation. Furthermore, the magnetic bias when the rotor is turned, i.e. during the measurement itself, is constant.
BRIEF DESCRIPTION OF THE DRAWINGS
Exemplary embodiments of the invention are represented in the drawings and will be explained in more detail in the following description.
A longitudinal section through a first exemplary embodiment with two ring magnets is represented in FIG. 1,
in FIG. 2 an exemplary embodiment of the measuring device with only one ring magnet,
in FIGS. 3 a third exemplary embodiment with a slit passing through the stator.
FIG. 4 shows the course of the measurement curve, i.e. of the induction B over the angle of rotation a with and without an additional magnet.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A stator is identified by 10 in FIG. 1 and is surrounded by a rotor 11. There is an air gap 12 between the stator 10 and the rotor 11, which should be as narrow as possible and in actuality is approximately 0.5 mm. The stator 10 and the rotor 11 are made of a magnetically conductive material of high permeability and low magnetic hysteresis. In the present case this can be soft iron, for example. The stator 10 furthermore has two slit-like air gaps 14, 15, which are located diametrically opposite each other, wherein at least one Hall element 16, by means of which the relative movements of the ro
REFERENCES:
patent: 4829248 (1989-05-01), Loubier
patent: 5444369 (1995-08-01), Luetzow
patent: 5869962 (1999-02-01), Kasumi et al.
Bielert Friedrich
Herden Werner
Patidar Jay
Robert & Bosch GmbH
Striker Michael J.
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