DE29923913U1 - Improvements to a magnetic field sensor working with a magnetic field probe - Google Patents

Description

1999G03605 DEOl

Description

Improvements to a magnetic field sensor using a magnetic field probe
5

The present innovation relates to improvements to a magnetic field sensor operating with a magnetic field probe, in particular with a Hall probe, which is preferably used to detect magnetic flux changes in/on an object and in particular as a sensor for measuring the speed and/or angular position of rotors and the like.

In a magnetic field sensor with, for example, a Hall probe, means are provided for generating a permanent and/or electromagnetic magnetic field. This field is generated using a permanent magnet or a current-fed magnetic coil. The Hall sensor is arranged between these on the one hand and the wheel, for example for the specific application, on the other. This is a Hall sensor of a conventional type with, for example, a semiconductor element. The tire surface of the wheel runs past the preferably stationary arrangement of permanent magnet/magnetic coil and Hall sensor at a predeterminable distance. As a rule, a marking element, e.g. a series of teeth, holes or other markings, is provided on this tire surface, which have properties that differ from their neighboring surroundings in terms of permeability. For example, these can be teeth made of magnetically permeable material or on the surface of the treadmill there is a band made of material with magnetic properties, in which there are recesses distributed in the direction of travel, in which the medium present there (e.g. air) has no or other properties that respond to a magnetic field. The number of effective markings passing the Hall sensor per unit of time, which cause a corresponding electrical signal in the Hall sensor, can be used to determine the speed or revolutions per unit of time.

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safety of the wheel. If two Hall sensors with separate signal detection are arranged next to each other in the direction of rotation, the direction of rotation of the wheel can also be determined, namely from the temporal sequence of the electrical signals generated in one and the other of the Hall sensors.

Such magnetic field sensors with Hall probes, which are at least known in principle, only work optimally if there is not too great a distance between the permanent magnet or magnetic coil and the Hall sensor on the one hand and the tire surface or markings on the wheel on the other.

Although there are other technical solutions that can be used to carry out reliable measurements even when the distance between the sensor and the impeller is greater, these solutions generally require more technical effort compared to an arrangement as described above. ■
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The purpose of the present innovation is to find or specify measures for an arrangement such as that described above and similar ones, with which larger distances between the impeller and the measuring arrangement of the type described can also be provided and nevertheless an exact measurement of the speed and/or current angular position and/or direction of rotation of the impeller can be achieved, for example at a close distance.

This problem is solved by the measures of patent claim 1 and further embodiments of the innovation emerge from the subclaims.

The innovation is based on the idea of a solution to provide additional flux feedback for the magnetic field of the permanent magnet in the described or a similar arrangement of permanent magnet or magnetic coil with Hall probe.

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or the electromagnetic coil, with which signals with a higher signal level can be obtained that occur and are to be evaluated due to flux density changes that are based on the rotation of the impeller prepared as described above. This flux feedback used in accordance with the innovation also has the further advantage that the stray field in relation to the sensor arrangement is drastically reduced and thus the electromagnetic compatibility (EMC) is also increased or improved. Further explanations of the innovation are described using the figures belonging to the disclosure content of this application.

Figure 1 shows in plan view (a) and two side views (b

and c) a first embodiment.

Figure 2 also shows a modified second embodiment.
Figure 3 also shows another modified third

From execution form.

Figure 4 shows an embodiment with varied flow guidance.

Figure 5 shows a view of an embodiment with a different flow path and

Figure β also shows another embodiment with a varied combination of magnet and flux guide. 25

The above-listed embodiments are equipped with permanent magnets. Electromagnets can also be used instead. However, the use of permanent magnets is preferred. These embodiments are also designed as differential sensors with two Hall sensors arranged adjacent to each other in the direction of travel of the wheel or the markings, with which, in a manner known per se, forward and reverse running and angular position can be quantitatively recorded in addition to the speed. It should be noted that the figures do not exclusively correspond to the rules of a workshop drawing, in particular

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especially with regard to the cuts and penetrations shown.

Figure 1 shows, with representation a, a plan view (sectioned according to section a-a in representation b) of an embodiment with, for example, a perforated band 11 with marking elements on the tire surface of the (not shown) wheel. It should be noted - valid for the entire application - that the terms used here, such as wheel, perforated band, recess, volume fraction, etc., are to be understood as respective exemplary embodiments. Instead of the wheel and/or the perforated band, a different carrier can also be provided for the markings. These markings do not have to be exclusively recesses, volume fractions, etc. on/in the carrier. This carrier can also be a linearly extending band or similar object (as shown in the figures) that runs along the sensor and whose linear speed is to be measured.

The Hall sensors and their positioning are designated with 21 and 22.

The marking elements 12 denote volume portions in the perforated tape 11, e.g. holes or cutouts provided, in which any medium present differs from the material of the perforated tape 11 in terms of its magnetic effect. For example, the material of the perforated tape 11 is paramagnetic or ferromagnetic and the material in the volume portion/cutout 12 is air. Conversely, the volume portions 12 can be magnetic and the material of the tape 11 is weakly or better non-magnetic.

In the side view b of Figure 1, which belongs to the plan view a and is cut according to section b-b in view a, the same details are designated with the same reference numerals. 33 designates a permanent magnet and 34 the associated

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1 shows a flux return according to the innovation, which together form a (so -called) E-shaped yoke 3. 35 designates the magnetic flux which is based on the presence of the permanent magnet 33 and runs in the flux return 34 and in the perforated strip 11. This flux return 34 causes a closed magnetic flux in relation to the permanent magnet 33 with the direction or course shown by the arrows indicated. In view b of Figure 1, only the Hall sensor 21 can be seen. From the second side view c of Figure 1 (see section cc in plan view A of Figure 1) it can be seen how the permanent magnet 33, the flux return 34 and the sensors 21 and 22 are arranged in relation to one another.

Neighboring markings or volume regions 12 are separated from one another by an intermediate surface region 112 of the surface of the perforated strip.

As can be seen from Figure 1, the Hall sensor 21 is located just above the material of the perforated strip 11 and the Hall sensor 22 is located above a recess 12 of the perforated strip 11. With this positioning, the Hall sensor 21 delivers a (larger) electrical signal because the magnetic flux 35 is better closed with the aid of the flux return 34 via the magnetic material of the perforated strip 11 than is the case for the area with the recess 12 for the position of the sensor 22.

Although, as can be seen from the illustration of the figure, there is a greater distance di, d2 between the Hall sensor 21 and the material of the perforated strip 11, this signal of the Hall sensor 21 is enlarged compared to known arrangements due to the innovative presence of the flux feedback 34 in accordance with the task of the innovation and is therefore easier to evaluate.

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From the above explanations it is clear that the respective air gaps di + d^ or d2 + d3 (see the figure) for the magnetic flux 35 (in the respective leg of the flux return 34) are small, compared to the respective much larger path portion wi or w ₂ (see again the figure), in which the (respective portion of the) magnetic flux there runs through non-magnetic material in the volume portion or in the recess 12.

Figure 2 shows, again in views a, b and c, an embodiment that is varied compared to Figure 1, with permanent magnets 133 and 133 ^λ instead of the only permanent magnet 33 of Figure 1. In accordance with this variation, views a and b of Figure 2 differ from those of Figure 1. It is clear from Figure 2 how the permanent magnets 133 and 133' extend in the longitudinal direction of the perforated strip, positioned above it, over the surface portion 12. The legs of the E-shaped yoke 3 of the flux return according to the innovation are designated 134, 134' and 134''.

Figure 3 shows, in the same way as Figures 1 and 2, with the same or similar reference numerals, a third variant with permanent magnets 233 and 233' in the position shown. The flux return of the yoke 3 is designated 234.

What these three embodiments have in common is that the permanent magnet 33 or the permanent magnet pairs 133, 133' and 233 and 233' extend equally over the areas of the two sensors 21 and 22. For the magnetic flux of the permanent magnet 33 of Figure 1 or the permanent magnet pairs 133, 233 of Figures 2 and 3, as a result of the flux return 35 provided in accordance with the innovation, there is a gap in the area of the perforated strip 11 outside a non-magnetically effective volume portion 12 thereof, ie in the area 112 and that of the sensor 21, which is only defined by the distances di or d ₂ and d3.

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An interrupted, i.e. largely closed, path for the magnetic flux 35 through permeable material is present. In the area of a volume portion 12 or the sensor 22 of Figures 1 to 3, however, the flux-weakening path portions W ₁ and W 2 are effective, which are caused by the non-magnetic volume portion 12. (If the magnetic effectiveness of the volume portion 12 and the material of the perforated strip 11 are swapped, these conditions and effects are reversed accordingly.)

Figure 4 shows an embodiment of the innovation in which the yoke 3' is designed with extended outer legs for the flux return 434 so as to laterally encompass the perforated strip 11. In this embodiment too, in the sense of the description for Figures 1 to 3, a high magnetic flux return is ensured for the area 112 between two volume portions 12 and, in contrast to this, as shown in Figure 4b, the flux-weakening path portions wi and W2 are present in the area of the volume portion 12 for the sensor 22.

Figure 5 shows two 90° side views a and b of a design with differential Hall sensors 21, 22 and with the yoke 3' with flux feedback 434 and permanent magnet 33. Instead of a perforated strip 11 (as in Figure 4), a rack 111 is shown here (in Figure 5a in side view). The representation of the rack also represents the image of the development of the circumference of a gear wheel. The two outer legs of the yoke 3' extend to the side of the rack 111 so far that the teeth 411, but only these, reach into the area of the magnetic flux 35 between the ends of the yoke 3'. Between the teeth 411 are the tooth gaps 412, which correspond to the (non-magnetic) volume portions or recesses 12 described above. It is clear that in the embodiment according to Figure 5, there is also a high magnetic flux feedback for the sensor 21, which is opposite a tooth 411. The opposite is the case for the sensor 22, which is opposite a tooth gap 412.

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Figure 6 shows a further modified embodiment of the principle of the innovation, in which the U-shaped yoke 3'' with the magnet 33 and the legs of the U-shape as a flux return 534 is again opposite a rack. Here, too, this can be a gear wheel that is unwound as
In the space between the one
Leg 534 and a tooth 411 and a tooth gap 412
are the two sensors 21 and 22, of which only the
Sensor 21 is opposite a tooth. For this sensor 21, the magnetic flux 35 and thus the signal is significantly higher than
This is the case for the sensor 22 with the magnetic flux weakening through the tooth gap 412.

Claims (10)

1. Magnetic field sensor for measuring magnetic flux changes on/in an object by means of a differential magnetic field probe ( 21 , 22 ) which is provided in the magnetic flux ( 35 ) of an arrangement with a permanent/electromagnet, characterized in that a flux return ( 34 ) made of magnetic material in the form of a yoke ( 3 ) with a magnet ( 33 ) contained therein is provided for the magnetic flux ( 35 ) to be closed across the object, wherein this flux return ( 34 ) is arranged and designed in the magnetic field sensor in such a way that an air gap (d ₁ , d ₂ , d ₃ ) for the magnetic flux ( 35 ) that is larger than is structurally unavoidable is avoided. 2. Magnetic field sensor according to claim 1, characterized in that the differential magnetic field probe comprises two Hall probes ( 21 , 22 ). 3. Magnetic field sensor according to claim 1 or 2, characterized in that the flux return ( 34 ) and the magnet ( 33 ) together form an E-shaped yoke ( 3 ) and the magnet ( 33 ) forms at least a portion of the middle leg of the E-shape. ( Fig. 1) 4. Magnetic field sensor according to claim 1 or 2, characterized in that the flux return ( 134 , 134 ', 134 ") and two magnets ( 133 , 133 ') together form an E-shaped yoke ( 3 ) and one of the magnets forms at least a portion of the respective rear part of the E-shape of the yoke between two adjacent legs. ( Fig. 2) 5. Magnetic field sensor according to claim 1 or 2, characterized in that the flux return ( 234 ) and two magnets ( 233 , 233 ') together form an E-shaped yoke ( 3 ) and each of the magnets forms at least a portion of one of the outer legs of the E-shape. ( Fig. 3) 6. Magnetic field sensor according to one of claims 3, 4 or 5, characterized in that the outer legs of the E-shaped yoke ( 3 ') are extended in such a way that they are designed to laterally surround the object ( 11 , 111 ). ( Fig. 4, 5) 7. Magnetic field sensor according to one of claims 1 to 6, characterized by arrangement in a device for measuring the rotational speed of an object ( 11 , 111 ). 8. Magnetic field sensor according to one of claims 1 to 6, characterized by arrangement in a device for measuring linear movement of an object ( 11 , 111 ). 9. Device with a magnetic field sensor according to one of claims 1 to 8, characterized by probe measurement on a perforated strip ( 11 ) of the object. 10. Device with a magnetic field sensor according to one of claims 1 to 8, characterized by probe measurement on a gear or a rack ( 111 ) of the object.