The invention relates to a magnet interconnection, in particular an encoder magnet for a magnetic field sensitive sensor, a position sensor, or an angle sensor.
Magnetic field sensitive sensors react to a magnet field of an encoder magnet that is arranged movable relative to an actual sensor, wherein the encoder magnet is typically configured as a permanent magnet or includes a permanent magnet. In exceptional embodiments it can also be an electromagnet.
Thus, only a portion of the magnetic field generated by the encoder magnet, namely only the magnetic use field emitted in use direction towards the sensor element is being utilized, whereas the magnetic field of the encoder magnet emitted in all other directions, thus the scatter directions, is not required but to the contrary, depending on its orientation and range, it can also affect the measuring result negatively.
Thus, it is insignificant as a matter of principle, whether the measurement value is in a rotation position, this means the sensor measures an angle, or the measurement value is a lateral position, this means the sensor measures a distance.
For an angle sensor, e.g. the direction of the magnetic field of the encoder magnet is determined touch free through one or plural Hall sensor or also through XMR sensors.
In linear sensors a position or movement of an encoder magnet relative to a reference position is determined touch free. Thus, the magnetic field can be determined directly through one or plural Hall sensors or XMR sensors, or indirectly e.g. through the saturation of magnetic cores (permanent-magnetic linear contactless displacement sensor—PLCD)
It is also feasible that the permanent magnet generates a pulse through its magnetic field, wherein the pulse is subsequently detected through an additional sensor element like it is the case e.g. for magnetostrictive position sensors.
In a position sensor of this type an encoder magnet, which can be mounted e.g. at a movable machine element, causes a magneto-elastic density wave, (MEDW) which propagates in a wave conductor arranged in the sensor. A time difference between the creation of the MEDW and its detection at one end of the wave conductor is used as a measurement value for determining a position.
The exact function of a position sensor of this type is sufficiently known, thus a detailed description can be omitted.
It is particular for all sensors actuated by permanent magnets and of particular interest for the present invention that the sensor characteristics are substantially determined by the type of the magnetic field of the encoder magnet (position magnet), this means not only through the maximum field strength and primary orientation, but also through its local shape and propagation.
Thus a position magnet with high field strength can have e.g. a greater distance between the position magnet and the sensor, than for a magnet with low field strength.
On the other hand side, a magnet whose field strength very limited in particular locations, can lead to a better position resolution for the sensor.
For example when an application requires plural position magnets at a sensor, a position magnet with a field strength that is very much reduced at particular locations is advantageous, since this indirectly determines the minimum distance between two adjacent position magnets.
For some types of sensors, in particular the direction of magnetization of the encoder magnet is relevant for the sensor principle, e.g. for angle sensors.
For other types of sensors, the dependency from the magnetization directions can rather be detrimental, since this can lead to sensor malfunctions when a user mixes them up. In situations like that, a symmetric design of the encoder magnet is preferred.
According to a particular configuration of the position sensor magnets can be used, whose magnetic orientations are aligned parallel to the sensor (so called axial orientation), or which are e.g. also aligned perpendicular to the axis of the sensor (radial orientation). Magnetic sensors are also provided in rod form, wherein the position magnet can have a locally variable orientation, and wherein the orientation is aligned radially to the sensor (so called radial orientation.
In order to improve the characteristics of position magnets for magnetic position sensors numerous proposals were made.
Von Stoll et al. propose e.g. in U.S. Pat. No. 5,514,961 to use an axially oriented ring magnet for a rod shaped sensor, wherein a steel ring is attached at the face of the magnet.
The steel ring is made from simple magnetizable steel which conducts the flux lines at one end of the magnetic ring as a flux conductor.
The flux lines at this location impact the sensor rod in a concentrated manner at a steeper angle and lead to a stronger and more defined magnetic pulse which provides a better function for the sensor.
The disadvantage of an axial magnet, however, is that the propagation of the magnetic field is not independent from the installed position of the magnet and thus the properties of the sensor depend on how the position magnet is oriented. Thus, the position magnet is not universally usable.
Another disadvantage is that the field strength of an axial magnet based on its orientation has a high percentage of flux lines parallel to the sensor rod which leads to a strong remote effect when the magnet is oriented incorrectly.
A remote effect of this type of the position magnet can e.g. degrade the sensor properties when the position magnet is proximal to the detector at an end of a magetostrictive wave conductor.
Another proposal is disclosed by von Sprecher et al. in U.S. Pat. No. 6,271,660 which discloses a particular arrangement to increase the use signal of the magnet.
This document uses a position magnet whose magnetic orientation is directed towards the position sensor (perpendicular/radial orientation) and combine the magnet with two additional magnets which are arranged in the same direction (also radial) parallel to the first magnet but which have opposite orientation so that the north pole of one magnet is placed adjacent to the south pole of the other magnet (anti-polar arrangement).
This arrangement facilitates to superimpose the sensor signals of the particular magnets in a magnetostrictive sensor so that the extremes of the signal are reinforced and thus the rate of change of the sensor signal is increased. However, no controlled superposition of opposite magnetic fields is provided.
This facilitates a greater distance between a magnet and a sensor. However, an arrangement of this type causes a greater width of the magnet since the width of the magnets should be substantially identical for an optimum superposition of the particular pulses.
The distance of the particular magnets is determined by the run-time of the MEDW in the wave conductor.
Additionally a non-magnetic gap has to be provided between the particular magnets since otherwise the anti-polar magnets would magnetically short one another which would cause a reduction of the available field strength.
Additionally the effect of unilateral field strength amplification was used first by J. C. Mallinson (J. C. Mallinson, One-Sided Fluxes A Magnetic Curiosity, JEEE Transactions on Magnets, 9,678-682, 1973).
A combination of magnets with a magnetization that is respectively offset by 90° is also known in the art as Halbach-Array and was used for guiding particle beams (K Halbach, Nuclear Instruments and Methods, 169, 1, 1980).
Subsequently Halbach arrays were used in particular for generating strong magnetic fields. Also using cylindrical shapes or spherical shapes is known in the art in order to generate substantially increased field strengths in the center of the cylinder or the sphere.
Thus it is the object of the present invention to provide a cost-effective and compact magnet interconnection, in particular for an encoder magnet for a magnetic field sensitive sensor which provides the following:
This object is achieved through the features of claims 1 and 10. Advantageous embodiments can be derived from the dependent claims.
The mutually interfering interconnection magnets with their deviating pole orientations which, however, do not add up to form a simple magnetic loop cause mutual interference of the magnetic field lines of the particular interconnection magnets in a manner so that the field strength of the magnetic interconnection in the desired direction of use is increased. As a consequence thereof, or even as one of the desired main effects also the scatter field in the scatter directions that are not being used shall be reduced.
This object can be achieved on the one hand side through a different actual arrangement of the pole orientations within the interconnection element as a function of the type of magnetic field sensitive sensor that shall be operated with the interconnection element, e.g. a position sensor that extends in one direction in which the useable magnetic field shall be oriented exactly transversely if possible or radially with respect to the longitudinal orientation of the sensor element, or an angle sensor in which the resulting magnetic field shall rotate the typically flat angle sensor in its plane, thus e.g. parallel to the tangential direction of the rotation axis of the angle sensor.
The actual configuration furthermore depends on whether the magnetic interconnection exclusively includes interconnection magnets or also interconnection elements which are no magnets themselves, wherein in turn a differentiation has to be made between magnetizable and known magnetizable elements of the interconnection. The magnetizable elements of the interconnection, e.g. soft iron focus the magnetic flux which is provided at this location anyhow and prevent further scattering of the magnetic flux, but do not change its orientation since the elements of the interconnection are only magnetized by the magnetic flux which is provided at this location anyhow.
Non-magnetizable elements of the interconnection, however, are being used merely as spacers between the interconnection magnets and form the magnetic field of the magnetic interconnection primarily with respect to its spatial dimension through the defined gap, however, they do not qualitatively change the field, thus e.g. with respect to its flow directions at respective locations.
The desired mutual interference of the configuration of the magnetic fields of the interconnection magnets thus is typically the greatest when e.g. for a symmetric arrangement of the interconnection elements at least the center elements, e.g. three elements are interconnection magnets, while the elements of the interconnection which join on the outside can be magnetizable or non-magnetizable elements of the interconnection, thus no interconnection magnets.
Mutual influencing of the magnetic fields as recited supra is e.g. facilitated in that, typically in top view of the plane in which the pole orientations of the interconnection magnets are arranged, the pole orientations in longitudinal direction of the magnetic interconnection change from one interconnection magnet to another respectively in the same direction, in particular respectively by 90°.
Overall, and in particular in view of this pattern, the interconnection magnets are preferably arranged in series, preferably in a straight line behind one another, wherein an uneven number of interconnection elements and in particular a symmetric configuration with respect to the center interconnection element has proven advantageous for most applications.
In order for the interconnection elements to permanently remain in their relative positions which is difficult to accomplish for magnets with different pole orientations which do not complement each other to form a magnetic rail due to the repulsive forces, the interconnection magnets can be glued together, e.g. in that they are inserted into a respective retaining device and subsequently completely incased into plastic material or loosely inserted adjacent to one another in a respective housing that encloses them in a form-locking manner which secures them in a particular position relative to one another. Also gluing the elements of the interconnection together is only possible at the mutual contact surfaces of the elements of the interconnection through a respective device. Theoretically also form locked connections of the elements of the interconnection relative to one another can be selected which, however, typically greatly increases manufacturing complexity.
A typical arrangement of the elements of the interconnection in which a resulting field line orientation in the center interconnection element is achieved transversely to the longitudinal direction of the element of the interconnection is characterized in that the interconnection magnets that are arranged on both sides of the center interconnection element have a pole orientation that extends in longitudinal direction of the magnetic interconnection but with pole orientations opposite to one another.
Thus, when the center element of the interconnection is not a magnet this causes a strong magnetic field that extends in all transversal directions relative to the longitudinal direction of the magnetic interconnection. However, when the center element of the interconnection is also a magnet whose pole orientation is oriented in a particular direction that is transversal to the longitudinal direction of the magnetic interconnection the magnetic field in this particular pole orientation is amplified and widened, in the opposite directions it is weakened and narrowed.
A configuration of the magnet interconnection of this type is e.g. particularly suitable for an encoder magnet arrangement at a magnetic field sensitive distance sensor, whose sensor element is e.g. a wave conductor in which the magnetic interconnection is moved with its longitudinal direction parallel to the longitudinal extension of the sensor element and moved along the sensor element.
Another typical configuration of the magnetic interconnection with at least three interconnection elements is characterized in that the interconnection magnets which join in outward direction on both sides of the center element of the interconnection are arranged with pole orientations parallel to one another and transversal to the longitudinal direction of the magnetic interconnection, but in turn with pole orientations that are opposite to one another. This creates a resultant magnetic field which has an orientation parallel to the longitudinal orientation of the magnetic interconnection at the level of the center element of the interconnection, however, it has the same strength and circumferential direction and in longitudinal direction at all locations.
Thus, when the center element of the interconnection is additionally also an interconnection magnet whose pole orientation, however, extends in the longitudinal direction of the magnetic compound, the resulting magnetic field at the level of the center element of the interconnection is thus amplified on one side of the circumference and spatially widened in radial direction and on the other side however weakened and spatially contracted.
Additional shaping of the magnetic field can be provided in that the magnetic interconnection includes flux conductor elements made from magnetizable material on all sides that differ from the direction of use, thus in all scatter directions, wherein the flux conductor elements focus the magnetic flux closely to the magnetic interconnection in the scatter directions and reduce the expansion of the magnetic flux in the scatter directions.
A magnetic interconnection with an even number of interconnection elements can also be produced according to these principles, wherein the magnetic interconnection includes e.g. only two interconnection magnets which, however, yields a non-symmetrical magnetic field which e.g. expands in a relatively wide manner in one scatter direction. In case this is not detrimental for the planned application, the complexity of fabrication and thus also the cost for producing the interconnection element can be reduced.
Embodiments of the invention are subsequently described in more detail in an exemplary manner with reference to drawing figures, wherein:
a illustrates a particular rod magnet 2 in which the magnetic field lines 6 internally extend from the south pole to the north pole as usual and additionally run back in a curved arc accordingly outside of the magnet from the north pole to the south pole so that respectively closed magnetic field lines are created, wherein the distance of the magnetic field lines from one another in the illustration is the smaller, the greater the magnetic field strength is at the respective location.
For a rod magnet this yields a torus shaped magnetic field about the pole orientation 6 of the magnet 2.
b illustrates a ring magnet 2′ in which the device 6′ extends at all locations parallel to the longitudinal direction 10 of the symmetry axis through the center of the ring magnet 2′.
Thus, significantly higher field strength and thus more closely adjacent field lines 8′ are achieved in the portions remote from the ring magnet 2′ in the interior free space of the ring magnet, then radially outside of the ring magnet. Contrary thereto the pole orientation 6′ extends in the ring shaped magnet 2″ according to
This creates a magnetic field in which the field lines 8″ are formed as a double torus, whose two halves are arranged symmetrical to a transversal plane 10′ orthogonal to the longitudinal direction 10 extending through the center of the ring magnet 2′.
The concentration of the field lines in the interior free space of the annular magnet 2″ thus is very small, while high field strength is provided on the longitudinal axis 10 axially outside of the portion of the magnet 2, 2″.
The known embodiments are being used in order to optionally achieve high or low field strength in the gap within the ring magnet or axially offset there from.
It is evident that all pole orientations are thus arranged in the same direction, either parallel to one another or opposite to one another.
The
a in turn illustrates two particular rod magnets 2a, b with their respective torus shaped field lines 8a, 8b and pole orientations 6a, 6b, wherein the rod magnets are illustrated remote from one another so that they do not interfere with other, wherein the pole orientations 6a, 6b intersect at right angles.
When the particular rod magnets 2a, b are moved closer together according to
In the direction of the resulting vector sum from the two particular pole orientations 6a, b of the interconnection magnets 2a, b a strong field strength is created in the summation direction oriented away from the interconnection magnet 4a, b, the use direction 7, on the other hand a very weak magnetic field is created in the direction oriented towards the magnetic interconnection 4.
In the use-direction 7, thus already an amplification of the magnetic field has been achieved, however, the scatter field in all other directions and thus in all directions about the longitudinal direction 10, the direction of the sequence of the particular interconnection elements 1a, b behind one another, is still very large, in particular it has the same size in all directions.
According to
Thus a magnetic interconnection 4 of this type is particularly well suitable for an encoder magnet 3 for a position sensor 11 whose sensor element is typically straight and elongated and in which the magnetic interconnection 4 is arranged so that its use-direction 7 extends in a radial direction and transversal to the extension of the position sensor 11.
The pole orientations 6b, 6c of the two interconnection magnets 2b, 2c connected laterally thereto are oriented transversal to the longitudinal direction 10 and thus parallel to the transversal plane 10′ of the magnet interconnection 4, which in turn yields an arrangement that is symmetrical to the center plane 10′, however the pole orientations 6b, 6c of the two outer interconnection magnets 2b, 2c are oriented opposite to one another.
This yields a magnetic field in which a strong partial torus that is arranged on the transversal plane 10′ is configured as a magnetic field on one side of the longitudinal direction 10, while only a very weak residual torus that is closely adjacent to the magnet interconnection remains on the opposite side. On the face sides of the magnetic interconnection 4 a respective scatter field is configured as a partial torus, wherein the faces are symmetrical to one another about the transversal plane 10′.
This yields a strong magnetic field in a use direction 7, wherein the use direction is parallel with but opposite to the pole orientation of the center interconnection element 2a and wherein the strong magnetic field is arranged remote from the magnetic interconnection 4 on one side of the longitudinal direction 10 and is in particular configured for arranging an angle sensor 12 in this portion whose measurement axis 12′ about which the angular position of the magnetic field shall be measure by the angle sensor 12 intersects the pole plane of the magnetic interconnection remote from the longitudinal direction 10 of the magnetic interconnection 4, wherein the measurement axis intersects the pole plane in particular in a perpendicular manner, wherein the pole plane is defined by the pole orientations 6a-c of the interconnection magnets 2a-c of the magnet interconnection 4.
The magnet interconnections 4 of
a illustrates a variation of the solution according to
b illustrates a variation of the embodiment of
c illustrates a solution with different dimensions for the two lateral interconnect magnets 5b, c which can be required in particular applications for non-symmetrical configurations of the magnetic field.
d illustrates an important additional variant in which the pole orientations 6b, c for the basic solution according to
Thus, a comparison of the field lines of
However, the magnetic field is configured with the same strength in use-direction 7.
Simultaneously, however, the extension of the magnetic interconnection is much smaller in the solution according to
a only illustrates the center interconnection element 4a of an interconnect magnet 5a, while the two interconnection elements 4b, c connected on the outside are made from magnetizable material but are not permanent magnets themselves.
Accordingly a magnetic field is generated that is rotation symmetrical to the longitudinal direction 10.
b however corresponds to the solution according to
In the solution according to
In
The embodiments of
Number | Date | Country | Kind |
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102010010388.8 | Mar 2010 | DE | national |