Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1999-01-14
2001-08-14
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207220, C324S207250
Reexamination Certificate
active
06275025
ABSTRACT:
A FIELD OF THE INVENTION
The invention relates to a magnetic position sensor in which at least two stator elements are arranged in a magnetic field and a magnetic field probe is located in the air gap between the stator elements, a means further including that follows the movement of an object being arranged parallel to the plane spanned by the stator elements.
BACKGROUND OF THE INVENTION
WO 92/10722 discloses a Hall-effect angle sensor which is able to output angle-proportional signals. The angle is acquired by means of a Hall probe which is located in an air gap formed between two semicylindrical or shell-shaped stator halves.
A rotor comprises two disk-type magnets which are magnetized in an alternating direction and are mounted over a return path disk. The rotor is located before the two stator halves in the axial direction. In this case, the magnetization direction of the magnets is perpendicular to the axis of rotation.
The magnetic flux which issues from the north pole of the disk-type magnet is distributed depending on the angular position of the stator halves with respect to the magnet halves before it enters the south pole of the magnet.
If the north/south axis of the magnet is parallel to the air gap, then approximately half of the magnetic flux will flow through each of the two stator halves. Virtually no flux passes through the air gap in this case. The measurement induction tends to zero.
If the north/south axis of the magnet is perpendicular to the air gap, then virtually the entire magnetic flux first of all enters one stator half, crosses the air gap, enters the second stator half and from there the south pole of the magnet. Consequently, the Hall probe records a measurement induction maximum.
Since the magnetic flux takes a path along which, in addition to the measurement air gap, it must also twice traverse the air gap between magnet and stator halves in the axial direction, fluctuations in this air gap, for example in the form of mechanical axial play, produce a great change in the measured value.
Consequently, the invention is based on the object of specifying a magnetic position sensor which is insensitive to displacements in the movable means in a direction other than the measurement direction.
SUMMARY OF THE INVENTION
According to the invention, the object is achieved by the fact that the means connected to the movable object is of two-part design, each soft-magnetic part having at least one segment and the soft-magnetic elements being connected to one another rigidly in a manner displaced relative to one another, with the result that the segment of the first element is located opposite a segment gap in the second element, the stator elements being arranged between the soft-magnetic elements and a magnet that generates the magnetic field perpendicular to the plane spanned by the stator elements being arranged between the soft-magnetic elements.
This asymmetrical structure of the means connected to the movable object results in generation of a magnetic compensating flux via the measurement air gap.
In a refinement, the means connected to the movable object is a rotor which is arranged in the axial direction with respect to the stator elements.
The rotor is of two-part design, each soft-magnetic rotor element having at least one circle segment, and the rotor elements being connected to one another rigidly in a manner rotated relative to one another, with the result that the circle segment of the first rotor element is located opposite a segment gap in the second rotor element, the rotor elements being arranged between the stator elements and a magnet that generates the magnetic field in the axial direction being arranged both between the rotor elements and the stator elements.
The advantage of the invention is that the rigid two-part rotor configuration prevents the effects of axial play on the sensor signal, since the two air gaps occurring between rotor and stator are simultaneously changed in opposite directions and, consequently, the sum of the air gaps is always constant.
In an advantageous manner, the sum of the two air gaps which are formed in the axial direction between the rotor elements and a respective stator element is small compared with the axial extent of the magnet, as a result of which the magnetic flux through the stator is supported.
In a refinement, the stator elements are likewise of circle segment-like design.
The outer radius of the circle segment of at least one rotor element approximately corresponds to the outer radius of the circle segment-like stator element. The rotor elements are characterized by two radii, the first radius approximately corresponding to the outer radius of a stator element and the second radius approximately corresponding to the radius of the magnet.
In this case, the magnetic field probe is arranged radially with respect to the rotary spindle of the sensor in the air gap between two stator elements.
In a development, the outer radius of the circle segment of at least one rotor element is less than the outer radius of a stator element. This enables the arrangement of the magnetic field probe axially with respect to the axis of rotation of the shaft of the sensor in the air gap between the two stator elements. The advantage of this arrangement is that the magnet can now be dimensioned optimally since the axial spacing between the two rotor parts can be varied freely.
A simplification in the assembly of the overall sensor is achieved if the circle segment of the first rotor element has a smaller angle than the segment gap between two stator segments.
The asymmetrical configuration of the rotor disk results in the magnetic flux being guided in a targeted manner via the two stator halves.
Since the angular dependence of the flux guidance is achieved not by way of the contour or magnetization of the magnet but by the asymmetrical configuration of the rotor, the requirements on the magnet are minimal.
The magnet merely has to generate an axially directed field. This field can optionally be generated by a rotatably mounted permanent magnet or a magnet which is positionally fixed with reference to the stator and, in this case, can be designed either as a permanent magnet or as an electromagnet.
In a development, the magnet is designed as a permanently magnetic ring magnet.
The ring magnet can be mounted in a particularly simple manner in the sensor if it is directly connected to the two stator halves in a positionally fixed manner.
In another refinement, the magnet is fastened on a continuous rotor shaft by being fitted onto said shaft.
In a further design, the two rotor disks are rigidly coupled by means of a nonmagnetic sleeve, a respective rotor disk being fixedly arranged on a part of a rotor shaft, which is divided into two.
In this case, the stator elements are arranged coaxially around the axis of rotation of the rotor shaft.
REFERENCES:
patent: 4204158 (1980-05-01), Ricouard et al.
patent: 4307544 (1994-09-01), None
patent: 0578299 (1994-01-01), None
patent: 0611911 (1994-08-01), None
patent: 2388248 (1978-11-01), None
patent: WO9210722 (1992-06-01), None
Mannesmann VDO AG
Mayer Brown & Platt
Snow Walter E.
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