Abstract
Encoders for bearing units are disclosed. In one example, an encoder includes a magnet part connected to a support part. The magnet part may have a U-shaped cross section formed by a plurality of magnets, wherein the plurality of magnets are situated in alternation with alternating magnetizations. An approximately homogeneous magnetic field may form in a cavity formed by the U-shaped cross section. A signal amplitude of the magnetization along an encoder circumference (U) and within the cavity may be nearly independent of a position of a magnetic-field-measuring sensor.
Claims
1. An encoder for bearing units, comprising: a magnet part connected to a support part; the magnet part having a U-shaped cross section formed by a plurality of magnets, wherein the plurality of magnets are situated in alternation with alternating magnetizations; wherein an approximately homogeneous magnetic field forms in a cavity formed by the U-shaped cross section; and wherein a signal amplitude of the magnetization along an encoder circumference (U) and within the cavity is nearly independent of a position of a magnetic-field-measuring sensor.
2. The encoder as claimed in claim 1, wherein the magnets comprise a first portion having a first L-shaped cross section and a second portion having a second L-shaped cross section, and wherein the first and second portions are differently magnetized.
3. The encoder as claimed in claim 1, wherein the magnet part is composed of a compound consisting of a support matrix and a magnetic filler, wherein the support matrix is composed of an elastomer, a thermoplastic polymer, or a thermosetting plastic, and wherein the magnetic filler contains hard ferrite, iron, rare earth, or a combination thereof.
4. The encoder as claimed in claim 1, wherein the magnet part rests against a leg of the support part in a planar manner.
5. A bearing unit comprising a sensor and an encoder as claimed in claim 1, wherein the sensor is situated in the cavity formed by the U-shaped cross section.
6. The bearing unit as claimed in claim 5, wherein a conversion of the magnetic field into an electrical signal is based on the principle of the magnetoresistive effect, the Hall effect, the use of field plates, the magnetoelastic effect, or the use of saturated core magnetometers.
7. The bearing unit as claimed in claim 5, wherein a signal evaluation in the sensor utilizes not only a zero crossing but also multiple switching thresholds, in order to increase a resultant resolution of output pulses for a speed detection.
8. The bearing unit as claimed in claim 5, wherein the sensor comprises multiple magnetic-field-measuring elements, wherein the sensor is designed for detecting not only a speed of rotation but also a direction of rotation.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The disclosure will now be described by way of example with reference to figures. Therein:
[0032] FIG. 1 shows a schematic view of a known encoder comprising a sensor,
[0033] FIG. 2 shows a section A-A through the encoder from FIG. 1,
[0034] FIG. 3 shows a schematic representation of magnetic field lines around the circumference of the encoder from FIG. 1,
[0035] FIG. 4 shows a signal strength-distance graph with respect to FIG. 2,
[0036] FIG. 5 shows a schematic view of an encoder according to the disclosure, comprising a sensor,
[0037] FIG. 6 shows a section B-B through the encoder from FIG. 5,
[0038] FIG. 7 shows a schematic representation of the magnetic field lines with respect to FIG. 6,
[0039] FIG. 8 shows a distance-signal strength graph with respect to FIG. 6,
[0040] FIG. 9 shows a graph for illustrating the signal evaluation in the case of a known bearing unit, and
[0041] FIG. 10 shows a graph for illustrating the signal evaluation in the case of the bearing unit according to the disclosure.
DETAILED DESCRIPTION
[0042] FIG. 1 shows the schematic view of a known encoder 100 comprising a sensor 16. The encoder 100 is installed in a bearing unit (not shown). The encoder 100 comprises a magnet part 5 connected to a support part 2. The magnet part 5 has a plurality of differently magnetized areas. The areas are designed as segments which are situated next to each other and have alternating magnetizations, wherein two areas form magnets 6, 7 in each case, which, in totality, form the magnet part 5.
[0043] As shown in section A-A according to FIG. 2, the magnets 6, 7 have an approximately rectangular cross section. A sensor 16 is situated at a distance 14 from the surface of the magnet 6 or the magnet part 5.
[0044] FIG. 3 shows the schematic representation of magnetic field lines around the circumference of the encoder from FIG. 1 along a circumferential portion U.
[0045] FIG. 4 shows the distance-signal strength graph with respect to FIG. 2. The distance 14 of the sensor to a magnet is plotted on the x-axis. A signal strength/amplitude of the encoder magnetic field detected by the sensor is plotted on the y-axis. The smaller images show the associated signal curves during rotation of the encoder; the magnetic signals have a sinusoidal shape along the circumference. The particular amplitudes are labeled with the points 21, 22, 23 in the distance-signal strength graph. The line 20 shown follows a function which is defined by the points 21, 22, 23. The signal strength is dependent on a distance 14 (according to FIG. 2) of the sensor 16 to the magnet part 5 of the encoder 1. That is, the further away the sensor 16 is from the magnet part 5, the lesser the signal strength is.
[0046] In technical applications, the resultant distance 14 is subject to very great tolerance influences. A resultant minimum signal is therefore correspondingly low. Therefore, only a reversal of the magnetic polarity (polarity reversal), e.g., the zero crossing in the signal, can be utilized for detecting the movement. Intermediate stages in the signal cannot be reliably evaluated, since the range of variation in the signal intensity is too great.
[0047] FIG. 5 shows the schematic view of an encoder 1 according to the disclosure, comprising a sensor 16. The encoder 1 is installed in a bearing unit (not shown). The encoder 1 comprises a magnet part 5 connected to a support part 2. The magnet part 5 comprises a plurality of magnets 6, 7. The magnets 6, 7 are situated annularly, one behind the other, with alternating magnetizations and form the magnet part 5. The magnet part 5 is designed to be annular in this case. The poles of the magnets 6, 7 of the magnet part 5 are situated in such a way that a positive pole of one magnet 6 always abuts a negative pole of another magnet 7, and vice versa.
[0048] As shown in section B-B according to FIG. 6, the magnets 6, 7 have a U-shaped cross section. The magnets 6, 7 are designed as horseshoe magnets. The magnets 6, 7 comprise a first portion 9 having a first L-shaped cross section and a second portion 10 having a second L-shaped cross section. The two portions 9, 10 are differently magnetized. The support part 2 comprises a first leg 3 and a second leg 4. One leg of each of the two portions 9, 10 rests against the leg 3 of the support part 2 in a planar manner. In this case, a contact surface 8 is formed between the leg 3 of the support part 2 and the legs of the two portions 9, 10. A sensor 16 is situated within the U-shaped cross section at a distance 13 from the surface of the magnet 6 or the magnet part 5.
[0049] FIG. 7 shows a schematic representation of the magnetic field lines with respect to FIG. 6. An approximately homogeneous magnetic field 15 is formed in a cavity 12 formed by the U-shaped cross section. Due to the provision of the U-shaped cross section, an approximately homogeneous magnetic field can be easily generated in the cavity 12 which is formed by the U-shaped cross section of the magnets 6, 7.
[0050] FIG. 8 shows the distance-signal strength graph with respect to FIG. 6. The distance 13 (according to FIG. 6) of the sensor to a magnet is plotted on the x-axis. A signal strength of the sensor is plotted on the y-axis. The line 30 shown follows a function which is defined by the points 31, 32, 33. The signal strength is nearly independent of a distance 13 (according to FIG. 6) of the sensor 16 to the magnet part 5 of the encoder 1.
[0051] This yields a resultant greater minimum signal. This signal can be utilized in a downstream signal processing step, in order to detect movement of the encoder, in that further switching levels, e.g., not only the zero crossing, are introduced.
[0052] A conversion of the magnetic field into an electrical signal is based on the principle of the magnetoresistive effect, the Hall effect, the use of field plates, the magnetoelastic effect, or the use of saturated core magnetometers (Foerster probe/fluxgate).
[0053] FIG. 9 shows the graph for illustrating the signal evaluation in the case of a known bearing unit. Strong fluctuations of the signal strength (magnetic field) are apparent. A reliable switching is possible only at the zero crossing 40. Resulting therefrom is a digital output signal having one pulse sequence 50 per pole pair.
[0054] FIG. 10 shows a graph for illustrating the signal evaluation in the case of the bearing unit according to the disclosure. Lesser fluctuations of the signal strength (magnetic field) are apparent. A reliable switching is possible not only at the zero crossing, but also at other levels 60. Resulting therefrom is a digital output signal having two pulse sequences 70 per pole pair.
LIST OF REFERENCE SIGNS
[0055] 1 encoder
[0056] 2 support part
[0057] 3 leg
[0058] 4 leg
[0059] 5 magnet part
[0060] 6 magnet
[0061] 7 magnet
[0062] 8 base
[0063] 9 portion
[0064] 10 portion
[0065] 11 snap hook
[0066] 12 cavity
[0067] 13 distance
[0068] 14 distance
[0069] 15 magnetic field
[0070] 16 sensor
[0071] 20 line
[0072] 21 point
[0073] 22 point
[0074] 23 point
[0075] 30 line
[0076] 31 point
[0077] 32 point
[0078] 33 point
[0079] 40 zero crossing
[0080] 50 pulse sequence
[0081] 60 level
[0082] 70 pulse sequence
[0083] 100 encoder
[0084] U circumference
