FIELD OF THE INVENTION

The present invention is generally related to the field of position sensors using a magnetic induction.

BACKGROUND OF THE INVENTION

Apparatuses for measuring a magnetic field property of a magnetic field are often referred to as magnetic field sensors or magnetic sensors. These kinds of sensors have a broad field of use. Often, these kinds of sensors are used in combination with magnetized objects or objects which influence a magnetic field in one way or another. Thereby, the magnetic sensors measure at least one property of the magnetic field either emanated by the object, i.e. originating from the object itself, or influenced by the object. Based on the measured at least one magnetic field property the position of the object is determined, thereby more than one measured at least one magnetic field property may be combined or processed to determine the position of the object. Therefore, these sensors are also often called position sensors. The most common position sensors are thereby linear and angular position sensors. A linear position sensor determines the position of the object on a linear path relative to the sensor whereas an angular sensor determines the angular orientation of such an object in the vicinity of the sensor. Furthermore, the sensors are also capable of determining a change in the position of the object, for example a motion of the object on a linear path or its rotation.

The position sensors can either perform direct or indirect measurements of the at least one property of the encountered magnetic field to determine the linear and/or angular position of the object. The measured property of the magnetic field allows quantifying the magnetic field, for example in terms of the magnetic field strength, its direction or the magnetic flux etc. and as such allows a determination of the position of the object, which either emanates the magnetic field or affects the magnetic field. For a direct measurement, for example, the magnetic field strength of the magnetic field encountered can be measured, whereas for an indirect measurement the magnetic flux can be measured by measuring a quantifiable property induced by the magnetic flux, for example an induced current or voltage.

Position sensors using direct measurements often times employ Hall elements, in order to measure the magnetic field strength of the encountered magnetic field and then determine the angular and/or linear position of the object based on the measured magnetic field strength.

Position sensors using indirect measurements often times employ inductive sensor elements, for example coils, in order to measure a property induced by the encountered magnetic field and then determine based on the measured induced property the angular and/or linear position of the object, which in this context is also often referred to as target. Inductive sensors rely on the physical effect of electromagnetic induction, wherein an electric field is generated in a coil by changes in a magnetic flux density. This arrangement enables the formation of a no-contact sensor, whereby a maintenance-free sensor can be produced. The magnetic field which induces the measured property can thereby either originate from the target, for example by eddy currents induced in the target itself, or can originate from a coil generating a magnetic field, which then couples via the target to at least one receiving coil.

Inductive position sensors have a long track record for reliable operation in difficult conditions. Consequently, they are often chosen for safety related, safety critical or high reliability applications, like e.g. in the automotive sector. Inductive magnetic sensors are not affected by static disturbing magnetic fields (static stray fields) from surrounding components, devices, apparatuses, or the environment in general. Nevertheless, these inductive magnetic sensors are still sensitive to alternating disturbing magnetic fields (alternating stray fields).

In recent years there is a growing trend towards miniaturisation of inductive sensors. This implies that if performance has to remain unchanged, the alignment tolerances between the coils constituting the sensor should scale as well. In particular, inductive sensors based on separate coils for transmission and reception of the inductive signals are very sensitive to coil alignment, as the relative position between transmit and receive coils greatly affects the direct coupling between them. This unwanted signal can be very strong if not managed correctly. This direct coupling is nothing else but the mutual inductance between the transmit and receive coils in the absence of a target device.

The manufacturing tolerances cannot always be reduced when the coils are made smaller. For example, for PCB (printed circuit board) based sensors there are clearly limits to the reduction of these tolerances. This means that the direct coupling between transmit and receive coils can become uncontrolled and introduce offsets much stronger than the signal amplitude.

Prior art rotary inductive sensors are often based on large coils. Given the relatively big dimensions of such sensors, misalignment between coils due for example to misalignment between the planes of the printed circuit board (PCB) containing the coils, is then no issue. However, use of such large coils cannot be maintained given the current trend towards miniaturisation. In that case a misalignment of for example 100 μm would have an impact which cannot be neglected anymore.

In U.S. Pat. No. 6,255,810 an inductive angle sensor is disclosed having two LC oscillators of an approximately identical design. By inductively coupling the oscillators, the oscillators synchronize themselves with respect to frequency and phase relationship so that undesirable mutual interference is prevented.

There is a need for inductive position sensors with a design suitable for miniaturization.

SUMMARY OF THE INVENTION

It is an object of embodiments of the present invention to provide for an inductive position sensor wherein coils are applied which are designed to have a substantially reduced sensitivity to manufacturing tolerances. It is a further object to provide an inductive position sensor wherein coils are applied wherein offset between calculated angular position and mechanical angular position is kept reduced.

The above objective is accomplished by the solution according to the present invention.

In a first aspect the invention relates to an inductive position sensor configured to determine a position of a target device, comprising at least two coils for determining said position, wherein at least two of the at least two coils for determining said position at least partially overlap, wherein at least one coil of the at least two at least partially overlapping coils is a transmitter coil and at least one of the at least two coils is a receiver coil and wherein at least one of the at least two coils has N2+Rportions substantially equally distributed over N substantially parallel planes, N being an integer larger than or equal to two and R an integer larger than or equal to zero, and whereby for each of said at least two coils said portions distributed over said N substantially parallel planes are substantially identical, so that mutual inductance between said at least two coils is substantially unaffected by misalignments between said N substantially parallel planes. The coils may actually be any inductive element, for example a wire, a wire in the shape of a coil, a wire in the shape of a spiral, or a wire in the shape of a helix, a loop, a multi turn loop, a solenoid, an inductor, or an array.

The proposed solution indeed allows for keeping the mutual inductance variation unaffected or almost unaffected. This is due to the design wherein the coils at least partial overlap, the coils having substantially identical portions substantially equally distributed over two or more parallel planes. Thanks to the specific arrangement proposed in this invention an increase in mutual inductance in one part of the inductive sensor is always compensated by a corresponding decrease in another part. Otherwise stated, the mutual inductance change, when the planes are translated one to another, between the portion of the first coil in the first plane and the portion of the second coil in the second plane should be substantially opposite to the mutual inductance change between the portion of the first coil in the second plane and the portion of the second coil in the first plane. Substantially opposite should be interpreted as that at least to a first order both mutual inductances have the same but opposite change. Moreover, due to the segmentation into N2+Rportions equally distributed over the various parallel planes in at least one of the coils acting as receive coil, it is ensured that on average a tilt in the receive coil is kept reduced. In this way angular errors are reduced or even avoided. Preferably all coils acting as receive coil are segmented into N2+Rportions.

In some embodiments of the present invention, the coils are considered to be substantially identical when the geometry of a coil can be obtained by plane symmetry and/or translations and/or rotations. It is important to mention that due to the presence of feeding vias and readout signals, some asymmetries are required for practical reasons, thereby introducing some asymmetry. Such vias and feeding lines should not be considered and therefore substantially identical coils might have discrepancies, in particular in their extremities. In alternative embodiments of the invention, the coils wire thickness and width may vary between identical coils up to 10% or up to 50% or up to 100% locally or in their full, although in some other embodiments the coils wires may have identical width and thickness.

In some embodiments of the present invention, coils are stated to be substantially equally distributed in a given number of planes if the length of the wires constituting the coils are of substantially the same length, or the length of the wires in the planes are in a range of +/−20% of the average length of the coils in each plane, or the length of the wires in the planes are in a range of +/−10% of the average length of the coils. It is important to mention that due to the presence of feeding vias and readout signals, some discrepancies between planes are required for practical reasons, so introducing some asymmetry in the lengths between planes. Such vias and feeding lines should not be considered when computing the length of a coil within a plane and therefore substantially equally distributed coils might have discrepancies, in particular in their extremities and/or top and bottom planes.

In a preferred embodiment one of the overlapping coils at least partially overlaps with all other coils of said at least two overlapping coils.

In an advantageous embodiment vias connecting for each coil the various portions of the plurality of portions distributed on said N substantially parallel planes are substantially in a set of M symmetry planes of the configuration formed by the at least two coils, whereby the M symmetry planes are orthogonal to the parallel planes.

In a preferred embodiment the number N of substantially equal planes equals two.

Preferably the portions of the at least two coils are substantially identical in size and/or in shape.

In embodiments of the invention the at least two coils are arranged to be connected to a feeding wire.

Advantageously, at least one coil is a transmitter coil and at least one coil is a receiver coil.

In a specific embodiment the inductive position sensor comprises six coils arranged to act as receiver coil and each comprising N1+Rportions in each plane.

In one embodiment each of the N substantially parallel planes is comprised in a printed circuit board or in a redistribution layer or in a leadframe.

In embodiments of the invention the inductive position sensor as previously described, is comprised in a package wherein the at least two coils are smaller than 10 mm×10 mm.

In embodiments of the invention all coils acting as a receiver coil have N2+Rportions.

In another aspect the invention relates to a system comprising an inductive position sensor as previously described and a target device arranged to rotate around a centre of geometry of the inductive position sensor.

In another aspect the invention relates to a method for an inductive position sensor configured to determine a position of a target device and comprising at least two at least partially overlapping coils each having a plurality of portions. At least one coil of the at least two coils is a transmitter coil and at least one coil is a receiver coil. At least one of the at least two coils has N2+Rportions, N being an integer larger than or equal to two and R an integer larger than or equal to zero. The method comprises distributing the portions substantially equally over N substantially, whereby for each of the at least two coils the portions distributed over the N substantially parallel planes are substantially identical and whereby the at least two coils are inside a package comprising the inductive position sensor. Preferably the package with the inductive position sensor also comprises a determination unit. Further the package may comprise a lead frame and passive capacitors for electromagnetic compatibility.

The method may also comprise a step of moulding the at least two at least partially overlapping coils and the determination unit in a single mould compound. Said mould compound may comprise a lead-frame partially extending outside said mould compound and may also comprise some integrated capacitor inside said mould compound.

For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

The above and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.

