EP2370790A1

EP2370790A1 - Magnetic encoder

Info

Publication number: EP2370790A1
Application number: EP09764496A
Authority: EP
Inventors: Heinrich Acker
Original assignee: Continental Teves AG and Co OHG
Current assignee: Continental Teves AG and Co OHG
Priority date: 2008-12-01
Filing date: 2009-12-01
Publication date: 2011-10-05
Also published as: US20110304324A1; DE102008059774A1; CN102227614A; WO2010063712A1; KR20110106329A

Abstract

The invention relates to a magnetic encoder comprising at least one encoder track (1, 3) having one or more pole pairs, the magnetization directions (2) of subsections within at least one of the poles (1, 3) being substantially characterized by a continuous and/or monotonic variation along the encoder track (1, 3).

Description

Magnetic encoder

The invention relates to a magnetic encoder according to O-berbegriff of claim 1, a method for producing a magnetic encoder according to the preamble of claim 8 and the use of the magnetic encoder in motor vehicle sensor assemblies.

Magnetic encoders are known, which are used in sensor arrangements for the direct or indirect measurement of variables such as angle of rotation, length or speed. These magnetic encoders are normally of permanent and hard magnetic design and have an encoder track with a plurality of pole pairs, the magnetic field of these poles being detected by one or more magnetic field sensor elements.

The information provided by the encoder about the measurand may generally be coded in the field direction and / or in the field strength. An evaluation of the field direction has the advantage that it is largely independent of temperature, while all permanent magnets show a temperature-dependent field strength. The magnetic field sensor elements also operate temperature-dependent. With regard to the measuring tasks, a distinction must be made between switching applications (state change when crossing a threshold of the measured variable) and measurements in the narrower sense. With regard to the use of such measurements in the strict sense, which can generally be characterized by the fact that a uniform sensitivity, resolution and accuracy in the determination of the measured variable is required over the measuring range, the magnetic encoders discussed and proposed here are preferably provided.

From the above requirement for uniform training and effect in connection with the measurement of the field direction, it follows that the field direction should change as linearly as possible with the measured variable. Any deviation from this causes an error or at least a correction effort in the measuring system. The usual design of encoders with respect to their calculation and magnetization relates to encoders with poles in the form of blocks, each pole corresponding to a zone with substantially homogeneous magnetization in terms of direction and intensity. With reference to FIGS. 1 and 2, such conventional magnetic encoder are illustrated.

A disadvantage of this block-like magnetization consists in the strong cross-sensitivity with respect to the reading distance or the normal distance of the magnetic field sensor element from the encoder track or the encoder surface. The function measured variable = f (field direction) is influenced by the fact that at a small distance in relation to the pole length, the magnetic field has magnetization direction changes only in the vicinity of the boundaries between the poles. At a large distance, on the other hand, by superimposing the field of several poles, one obtains a reasonably uniform rotation over the Value range of the measured variable or along the encoder track, as it is metrologically desired.

For the design of sensor arrangements for field direction measurements with the known block-like magnetized encoders, the following requirements or rules of thumb must be satisfied: The reading distance or the air gap between the encoder surface or encoder track and magnetic field sensor element should correspond to at least half the pole length of the encoder. The material thickness of the encoder should also be at least half the pole length.

However, these requirements conflict with the following restrictions:

Each encoder generates the highest field strength directly on its surface. There, the field direction is also the most precise embossed by the encoder, because external interference fields have a smaller share of the total field - at a distance of half the pole length, the field strength is already much lower and thus the susceptibility higher.

With a relatively large reading distance, for example the above-mentioned air gap of at least half a pole length, a part of the encoder material is used solely to generate a sufficiently strong field so that the magnetic field sensor element can still detect the magnetic field of the poles.

Encoders with a high material thickness, such as for example with a thickness of at least half a pole length, can be relatively poorly magnetized completely. The higher the requirements for the sensor arrangement, the stronger the target conflict with respect to the reading distance becomes: greater distance means a gain in linearity, but a loss of field strength and thus a deterioration of the signal-to-noise ratio or signal-to-noise ratio at the magnetic field sensor element.

The object of the invention is to propose a magnetic encoder which at least partially overcomes or at least reduces the above requirements and / or restrictions.

This object is achieved by the magnetic encoder according to claim 1 and the method according to claim 8.

The invention is preferably based on the idea of proposing a magnetic encoder with at least one encoder track, which comprises one or more pole pairs, wherein at least one pole has at least one magnetization which comprises monotone and / or continuously changing magnetization directions along the encoder track. These magnetization directions are assigned in particular to adjacent subareas of the pole along the encoder track.

As a result, a substantially linear relationship between field angle or detectable magnetic field and measured variable or relative position between encoder and a magnetic field sensor element already exists on the surface of the encoder. For this reason, when using the magnetic encoder according to the invention in a sensor array for Feldwinkel- / Feldrichtungserfassung the reading distance or air gap between the encoder and magnetic field sensor element can be kept relatively low, that is much smaller than half a pole length. In addition, therefore, only a relatively small proportion of Rialstärke des Encoders needed, which allows a cost reduction and the immunity to interference and the signal-to-noise ratio of the sensor array is also improved by the now applicable small air gap length.

The encoder track preferably runs along a measuring direction or a magnetically impressed scale of the encoder and / or is expediently composed of the successive poles.

The magnetic encoder is expediently designed as a permanent magnet made of hard magnetic material.

The magnetization direction preferably relates to the course direction of the encoder track, that is to say the magnetization direction is always related in particular to a tangent to the encoder track that is applied in the respective subarea.

The poles of the magnetic encoder are preferably not block-like and / or homogeneously magnetized.

The magnetization directions of the subareas within two successive pole lengths along the encoder track are preferably so pronounced that these magnetization directions essentially represent a rotation through 360 °.

The respective changes of the magnetization directions, in particular of all magnetization directions, of adjacent subareas of one or more or all poles along the encoder track are preferably substantially continuous. It is preferred that the respective change in the magnetization directions of adjacent subareas of one or more or all poles along the encoder track is substantially linear with respect to the corresponding path length change along the encoder track.

A subregion is preferably understood to mean a region of the one or more or all poles, which is formed infinitely narrow, in particular strip-shaped, along the encoder track.

It is preferred that at least within the subregions in a middle segment of a pole, which includes 50% of this length with respect to the pole length along the encoder track and bounded by two edge segments of this pole comprising 25% of the pole length on both sides, the magnetization directions of these subregions in the middle Segment of this pole substantially a rotation of at least 45 °, in particular at least 70 °, more preferably from 90 ° ± 5 °, imaging and / or that the magnetization directions of the two outermost portions of the middle segment of this Pols at least 45 °, in particular at least 70 °, particularly preferably of 90 ° ± 5 °, are mutually pronounced or rotated against each other, wherein the magnetization directions are always based on the respective course direction of the encoder track. Most preferably, the magnetization directions of these subregions form a rotation of substantially 90 ° in the middle segment of this pole. The encoder track is expediently curved, in particular ring-shaped, formed or alternatively preferably formed substantially straight.

The encoder track and / or the encoder are preferably formed substantially corresponding to one of the following geometric shapes: ring, ring segment, flat cylinder, cuboid, long cuboid, flat, disc-shaped cuboid, cylinder, long cylinder or half cylinder, divided along the longitudinal axis.

It is preferred that the method be further developed by mechanically moving the raw coder past the field magnet in a rotational movement along the magnetization path and to move the field-generating means in rotation about its own axis in superposition.

The magnetizing web is expediently understood to mean a web along the encoder track to be magnetized.

The field-generating means is preferably designed as a permanent magnet or alternatively preferably as a coil or coil arrangement, in particular as a superconducting coil or coil arrangement.

The raw coder is preferably formed at least partially from ferrite.

The method for producing a magnetic encoder is expediently carried out by means of a magnetization device which has two drives or drive means, one of which is the movement of the raw encoder or the field generating means along the magnetization path and the other causes and enables the rotational movement of the field generating means about its own axis. In particular, the drives are designed as stepper motors. The magnetization device is expediently designed for prototype production, whereby in each case no special or only for magnetizing a special encoder designed tool must be used to magnetize different encoders, such as differently designed raw encoders and / or different magnetization patterns.

It is appropriate that the field generating means is rotatably suspended with respect to an axis and in this respect can be rotated so that the field direction changes. The unmagnetized encoder or raw encoder is fastened in a holder in which it can be moved in the same direction as in a finished sensor arrangement in a rotational or translatory manner with respect to the direction of the pole change and the measured variable. Now, the raw encoder and the field generating means are moved so that an angle of the field generating means belongs to each value of the measured quantity, just as in the finished sensor arrangement. If the field generating means is in the immediate vicinity of the encoder surface, the encoder is magnetized in the required manner.

The invention also relates to the use of the magnetic encoder in automotive sensor assemblies, particularly in rotary sensor assemblies.

The magnetic encoder is preferred for use in sensor Soranordnungen provided which are used as path and / or position and / or angle and / or speed sensor arrangements in the automotive sector, in automation technology or in robotics. In particular, the use is provided in steering angle sensor assemblies in motor vehicles.

Further preferred embodiments will become apparent from the subclaims and the following descriptions of exemplary embodiments with reference to figures.

It show in a schematic representation

1 shows an exemplary, annular, magnetic encoder according to the prior art,

2 shows an embodiment of a conventional rod-shaped encoder,

3 shows an exemplary annular encoder with magnetization directions rotating continuously along the encoder track,

4 shows an embodiment of a rod-shaped, straight encoder with magnetization directions continuously rotating along the encoder track,

5 shows an exemplary graph of the magnetization direction as a function of the normalized path length along the encoder track in relation to an encoder with block-like magnetization and to an encoder with an encoder track along the encoder track. continuously rotating magnetization directions, and

Fig. 6 is an exemplary magnetization device.

Fig. 1 shows an annular encoder with six poles and Fig. 2 is a linear or straight encoder with six poles, both formed in a conventional manner. The magnetization directions 2 of individual portions of the poles 1 are shown by arrows. The poles 1 are magnetized homogeneous or block-like. The encoders therefore have an alternating north-south magnetization. The stringing together of the poles forms, for example, the encoder track.

An unrepresented magnetic field sensor element detects the block-like or box-profile-like magnetizations of the poles via their homogeneous magnetic field in the near range or at a relatively small air gap. Only with a relatively large air gap, the magnetic field sensor element can perform an angle measurement in which the detected angle of the magnetic field along the encoder track rotates reasonably evenly, as superimpose the magnetic fields of the adjacent and surrounding poles at a relatively large distance from the encoder track. However, this requires a relatively strong magnetic field of the encoder.

In Fig. 3 is an exemplary annular encoder with along the encoder track continuously rotating magnetization directions 2, which are isolated or exemplified as arrows illustrated. The encoder track runs thereby exemplarily along the dashed center line 3 of the ring or is by the juxtaposition the pole 1 formed. The magnetization of the encoder and of the poles 1 is designed such that the respective changes in the magnetization directions 2 of adjacent partial regions of the poles 1 along the encoder track are linear and continuous to the path along the encoder track or to the path along the dashed center line 3. Therefore, an unillustrated magnetic field sensor element can detect a uniformly rotating magnetic field along the encoder track even at a relatively small air gap and independently of the air gap length, whereby a radial angle measurement is substantially independent of the air gap length possible.

Based on the pole 4, the magnetization of the poles 1 will be explained in more detail by way of example. Pol 4 can be subdivided into a middle segment 5 with 50% of the pole length and two border segments 6 delimiting this middle segment 5, each with 25% of the pole length. Within this middle segment 5, the magnetization directions 2 of the partial regions form a rotation of substantially 90 °, which is realized in a real encoder by manufacturing inaccuracies, for example as a rotation of 90 ° ± 5 °. In other words, the magnetization directions 2 of the two outermost subregions 7 of the middle segment 5 of this pole 4 are mutually pronounced against one another by substantially 90 ° or 90 ° ± 5 °.

By way of example, the subregions are actually formed infinitely narrow along the encoder track, which, however, can not be represented concretely. 4 shows an embodiment of a straight encoder with a magnetization, as explained with reference to FIG. 3. It likewise has corresponding poles 1 and magnetization directions 2 of partial regions whose rotational profile along the encoder track can be seen in detail on the basis of an exemplary pole 4. This pole 4 is likewise subdivided into a corresponding middle segment 5 and two edge segments 6.

In FIG. 5, for clarity, the field direction Φ in degrees is plotted against the normalized encoder track length L / L _max , ie the measured variable or the field line profile detected by a magnetic field sensor element along the encoder track of a sensor arrangement (not shown). The solid curve represents a block-like magnetized encoder according to the prior art, measured directly on the surface, with the idealization of block-like poles of FIG. 2. The dashed curve represents the same encoder at the same distance, but taking into account in the Reality always present transition zone between the poles. The dotted curve represents the field direction curve of an exemplary inventive encoder according to FIG. 4 with respect to a relatively freely selectable air gap. This dotted curve likewise represents the field line profile of a conventional block-type magnetized encoder detectable by a magnetic field sensor element in an idealization and at a relatively large air gap if the above rules of thumb regarding the encoder design are met.

In Fig. 6 is an exemplary magnetizing apparatus for producing a magnetic encoder with along the Encoder track continuously rotating magnetization directions shown. Rozencoder 8 and the unmagnetisierte encoder is mounted about its center 11 so that it is rotationally movable in the direction of the associated arrow. Field generating means 9, designed as an example according to the invention as a rod-shaped permanent magnet, is rotatably mounted with respect to the axis 10.

For magnetization, both motions are carried out coordinated with each other so that each region of the raw encoder 8, when rotated by 11, reaches a point below the field-generating means 9 at a time when the field-generating means 9 is in the proper angular position. After a complete revolution of the encoder whose magnetization, for example according to FIG. 3, completed. Field tool 9 performs exactly three revolutions during one 360 ° revolution of the encoder. By means of this method, it is easy to realize different encoders of different pole numbers with the same structure. Only the gear ratio or the relative angular velocity of the drives need to be changed, e.g. easy to achieve with stepper motors.

In one embodiment, not shown, the field generating means is additionally arranged displaceable or mounted with respect to its axis, whereby an adjustment in terms of Rozencoderdurchmessers is easy to carry out.

Claims

claims

1. Magnetic encoder with at least one encoder track

(1, 3), comprising one or more pairs of poles, characterized in that the magnetization directions (2) of subregions within at least one of the poles (1,4) along the encoder track (1, 3) substantially continuously and / or monotonically changing pronounced are.

2. Magnetic encoder according to claim 1, characterized in that the magnetization directions (2) of the subregions within two consecutive pole lengths along the encoder track (1, 3) are so pronounced that these magnetization directions (2) substantially a rotation through 360 ° depict.

3. Magnetic encoder according to claim 1 or 2, characterized in that the respective changes of the magnetization directions (2) of adjacent portions of one or more poles (1, 4) along the encoder track (1, 3) are substantially continuously extending.

4. Magnetic encoder according to at least one of claims 1 to 3, characterized in that the respective change in the magnetization directions (2) of adjacent portions of one or more poles (1, 4) along the encoder track (1, 3) substantially linear to a corresponding one Path length change along the encoder track (1, 3) is pronounced.

5. Magnetic encoder according to at least one of claims 1 to 4, characterized in that the partial regions of the one or more poles (1, 4) infinitesimally narrow along the encoder track (1, 3) are formed.

6. Magnetic encoder according to at least one of claims 1 to 5, characterized in that at least within the subregions in a middle segment (5) of a pole (4), which with respect to the pole length along the encoder track (1, 3) 50% of this length The magnetization directions (2) of these subregions in the central segment (5) of this pole substantially rotate at least 45 °, in particular at least 70 °, and / or that the magnetization directions (2) of the two outermost subregions (7) of the middle segment (5) of this pole are at least 45 °, in particular at least 70 °, mutually or rotated against each other, the magnetization directions always being pronounced are related to the respective course of the encoder track.

Magnetic encoder according to claim 1, wherein the encoder track is curved, in particular ring-shaped, or substantially straight.

8. A method for producing a magnetic encoder, in particular a magnetic encoder according to any one of claims 1 to 7, wherein a raw encoder (8), which at least partially magnetizable ausge- is the magnetic field of a field generating agent

(9), characterized in that the field generating means (9) is rotatably mounted, wherein the raw encoder (8) is magnetized by the field generating means (9) and / or the raw encoder (8) at a defined distance relative to each other for generating an encoder track (1, 3) is / are moved on a defined magnetization path and the field-generating means (9) is thereby rotated around itself in a defined manner.

9. The method according to claim 8, characterized in that the raw encoder (8) in a rotational movement along the magnetization path on the field generating means (9) is moved mechanically guided past and the field generating means (9) to superimpose about its own axis

(10) is moved in rotation.

10. Use of the magnetic encoder according to at least one of claims 1 to 7 in motor vehicle sensor arrangements, in particular in rotation angle sensor arrangements.