DE3302084A1 - Inductive rotation sensor - Google Patents

Abstract

An inductive rotation sensor is described, consisting of a rotor (1) having Wiegand wires (5) distributed on its circumference, and of a stator (3) in which four magnetic pole pairs (6 to 9) are arranged juxtaposed with alternating polarity, which excite the Wiegand wires (5) passing by, asymmetrically. The Wiegand pulses are picked off by an electrical winding (20) which is arranged in the stator (3) between the two inner magnets (6, 7). <IMAGE>

Description

Description :.

The starting point of the invention is an inductive rotary encoder with the features specified in the preamble of claim 1. Such a rotary encoder is known from DE-OS 21 57 286. It has a rotor that serves as the axis of rotation parallel Wiegand wires, which with each other are arranged equally spaced on a cylindrical surface.

Wiegand wires are homogeneous, ferromagnetic wires (e.g. made of an alloy of Iron and nickel, preferably 48% iron and 52% nickel, or an alloy of iron and cobalt, or au :; an alloy of iron with cobalt and nickel, or of an alloy of cobalt with iron and vanadium, preferably 52% cobalt, 38% iron and 10% vanadium), which, as a result of a special mechanical and thermal treatment, have a soft magnetic core and a hard magnetic core Have a cladding, i.e. the cladding has a higher coercive force than the core. Wiegand wires . typically have a length of 10 to 50 mm, preferably 20 to 30 mm. Teaches a Wiegand wire the direction of magnetization of the soft magnetic core with the direction of magnetization of the hard magnetic core Jacket coincides, in an external magnetic field, the direction of which coincides with the direction of the wire axis, the direction of magnetization of the Wiegand wire is opposite, then when one is exceeded Field strength of approx. 16 A / cm reverses the direction of magnetization of the soft core of the Wiegand wire. These Reversal is also known as reset. at

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When the direction of the external magnetic field is reversed again, the direction of magnetization of the core is reversed Exceeding a critical field strength of the external magnetic field (which is called the ignition field strength) again so that the core and the jacket are magnetized in parallel again. This reversal of the direction of magnetization takes place very quickly and goes with a correspondingly strong change in the magnetic flux of force per unit of time (Wiegand effect). These A change in the flow of force can occur in an induction winding, which is referred to as a sensor winding short and very high (depending on the number of turns and load resistance of the induction coil up to approx. 12 Volt high) voltage impulse (Wiegand impulse).

When the core is reset, a pulse is generated in the sensor winding, albeit with a substantial amount lower amplitude and with the opposite sign than in the case of folding over from the antiparallel in the parallel direction of magnetization.

Is the Wiegand wire in a magnetic field, the direction of which is reversed from time to time and so soft What is strong is that it first re-magnetizes the core and then also the cladding and in each case down to the magnetic one Can bring saturation, then Wiegand pulses occur as a result of the flipping of the magnetization direction of the soft magnetic core alternating with positive and negative polarity and one speaks of symmetrical Excitation of the Wiegand wire. Field strengths are required for this from approx. - (80 to 120 A / cm) to + (80 to 120 A / cm).

The magnetic reversal of the jacket also occurs suddenly and also leads to a pulse in the Sensor winding, however, the impulse is much smaller than that induced when the core is flipped over Pulse.

However, if one chooses one as the external magnetic field, which is only able to move the soft core, but not the hard cladding in its direction of magnetization to reverse, then the high Wiegand impulses occur only with constant polarity and one speaks of asymmetrical excitation of the Wiegand wire. This requires a field strength of in one direction at least 16 A / cm (for resetting the Wiegand wire) and a field strength in the opposite direction from approx. 80 to 120 A / cm.

It is characteristic of the Wiegand effect that the pulses generated by it are largely independent of the rate of change in amplitude and width of the external magnetic field and have a high signal-to-noise ratio.

Other structures are also suitable for the invention bistable magnetic elements, if they have two magnetically coupled areas of different hardness (coercive force) and in Similar to Wiegand wires by induced, rapid flipping of the soft magnetic area can be used to generate pulses. For example, from DE-PS 25 14 131 is a bistable magnetic switch core in the form of a

Known wire, which consists of a hard magnetic core (e.g. made of nickel-cobalt), from a deposited on it electrically conductive intermediate layer (e.g. made of copper) and a soft magnetic layer deposited on it Layer (e.g. made of nickel-iron). Another variant also uses a core from one Magnetically non-conductive metallic inner conductor (e.g. made of beryllium copper) on which then the hard magnetic layer, then the intermediate layer and then the soft magnetic layer can be deposited. This well-known bistable magnetic switch core However, it generates lower switching pulses than a Wiegand wire.

The jacket surface of the rotor according to DS-OS 21 57 there is a stator opposite, which has two pairs of magnetic poles arranged approximately coplanar with the axis of rotation has, which are formed by two antiparallel to each other lying horseshoe magnets, the PoI surfaces face the outer surface of the rotor.

The horseshoe magnets are chosen so strong and so tight arranged on the rotor that they symmetrically excite the Wiegand wires moved past them during the rotor rotation .

The antiparallel orientation of the horseshoe magnets creates a static magnetic field, which in a between the pairs of magnetic poles has a zero crossing associated with a reversal of direction of the has magnetic field strength .; this area is hereinafter also referred to as the neutral zone of the magnetic field

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designated. The Wiegand wires cross the neutral zone and this causes their abrupt reversal of magnetization, which each time with a brief change; Force flow is linked, which in an el ^ k tr Lr. without winding, hereinafter also referred to as sensor winding, generates an electrical voltage pulse, precisely the Wiegnnd pulse, provided the changing force flow. ^J. dur ¹ II the winding hLnd goes through.

The symmetrical excitation allows from the Pnlrtril.it. the Wiegand impulses to recognize the direction of rotation of the rotor, because this is reversed. a reversal of the direction of rotation also around.

In order to have high Wiegand pulses in the sensor winding care must be taken to ensure that the occurring when magnetizing the Wiegand wires The change in force flux is as strong as possible in the sensor winding has an effect, i.e. at the moment of the reversal of the magnet there should be as close a coupling as possible between the respective Wiegand wire and the sensor winding. According to DE-OS? 1 S7 '-'86, the gen therefore in the neutral zone and ir-.t. wound on a ferromagnetic core, both of which are linden as close as possible to the jacket Π ächp 'of the rotor :; -and near are brought up to the ends of the Wiegand wires. Further It is important that the Wiegand wires are always at exactly the same point in front of the stator in their magnet.

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fold direction. Um d ier, / grant 1 one, r.o I 1 I 'Mi:; I the Wiegand wires when crossing the neutral zone

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move in a magnetic field with the greatest possible field strength gradient. This is also important when one a high angular resolution (smallest Central angle that two Wiegand wires are allowed to have so that the Wiegand impulses emanating from them still exist separately identifiable) wants to achieve. This enables a steep field strength ■ curve in the neutral zone try to achieve that the two magnetic pole pairs that are coplanar with the rotor axis are as possible close together. Any approximation of the magnetic pole pairs are in the present case, however Limits are set because they weaken each other due to their anti-parallel orientation, i.e. the Strength of the magnetic field generated by the Wiegand wires traverse decreases as these magnetic poles approach each other. But it must be guaranteed that the field strength necessary for the continued excitation of the Wiegand wires is maintained in any case. in the The case of DE-OS 21 57 286 is at least 80 A / cm for the symmetrical excitation of the Wiegand wires. Around. high and stable Wiegand impulses (i.e. the same amplitude as possible) are to be obtained but still strive for higher field strengths, which the Wiegand wires after each reversal of the direction of magnetization saturate again.

In the case of the rotary encoder known from DE-OS 21 57 286, therefore, in addition to the two, they are oriented anti-parallel Magnetic pole pairs at some distance from them (each about 120 ° angular distance based on the rotor axis) two more further, also stationary magnets are provided, which are antiparallel to each other, but i.w. parallel to associated with them adjacent to the sensor winding

Magnetic pole pairs are oriented, and which serve solely to guide the Wiegand wires before and after they are flipped over to bring the direction of magnetization into a state of high magnetic saturation, what with the closely adjacent inner magnetic pole pairs assigned to the sensor winding because of their mutual influence not possible.

The invention is based on the object of improving an inductive rotary encoder of the type mentioned at the outset in such a way that that while maintaining the dependence of the polarity of the Wiegand pulses on the direction of rotation of the rotor to achieve high and stable impulses as well as an improved angular resolution the inner magnetic pole pair 'each other can be further approximated.

This is achieved by a rotary encoder with the features listed in claim 1. Advantageous further training of the invention are the subject of the sub-claims.

According to the invention, the two inner magnetic pole pairs of the stator can be arranged so closely adjacent that as a result of their mutual influence that of them The magnetic field generated is no longer sufficient, the direction of magnetization of the Wiegand wires. Completely, i.e., both in the hard shell and in the soft core, to reverse, but still enough to make one To reset Wiegand wire magnetically, i.e. the direction of magnetization of the soft magnetic core of

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the parallel to the anti-parallel orientation based on the hard magnetic sheath of the Wiegand wire to reverse. To do this, you only need about a fifth of the amount required for the simultaneous remagnetization of the hard magnetic jacket required ^ field strength, and this clearly shows how much closer than in the rotary encoder known from DE-OS 21 57 286, the inner magnetic pole pairs are arranged to one another can be. This is also necessary in the case of asymmetrical excitation after the occurrence of a Wiegand impulse Renewed saturation of the respective Wiegand wire is caused by the two adjacent inner magnetic pole pairs further two magnetic pole pairs, which are also referred to below as outer magnetic pole pairs. The outer Magnetic pole pairs are i.w. antiparallel to each other and to the respectively adjacent inner magnetic pole pair oriented.

The advantages of the invention over a rotary encoder according to DE-OS 21 57 286 are that by the Closely moving the inner pairs of magnetic poles together, the point at which the Wiegand wires fold over and generate the characteristic Wiegand impulse, is very precisely and closely defined; this allows on the one hand a high angular resolution of the rotary encoder, on the other hand the sensor winding can be at this point be coupled very closely, either by arranging them directly next to them, and / or by arranging the winding on a ferromagnetic core, the ends of which are up immediately in front of the point in the area of the neutral zone

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leads where the passing Wiegand wires create the Wiegand pulse. This will result in high and stable Wiegand impulses, on top of that simply because of the choice of asymmetrical excitation are significantly higher than in the case of the DE-OS 21 57 286. It is the merit of the inventor. to have recognized that all of these advantages are achieved let, if one - starting from a rotary encoder known from DE-OS 21 57 286 - only the Reverses the polarity of the two outer magnets used for saturation. These only when viewed expost ostensibly simple reversal, however, fundamentally changes the functional principle of the rotary encoder and in an extremely advantageous manner.

■ The two outer pairs of magnetic poles, which serve to saturate the Wiegand wires, should preferably be used be moved close to the two inner magnetic pole pairs. "As close as possible" is to be understood as that the distance between the outer magnetic pole pairs and the inner magnetic pole pairs is still so great and their mutual The weakening is so small that the field strength generated by the two outer magnets Magnetic fields are so great that the Wiegand wires passing by them saturate them to a high degree for which the Wiegand wires should be exposed to a field strength of around 120 A / cm or more. It has been shown that the four magnetic pole pairs taken together can be closer together than this is the case with a rotary encoder according to DE-03 21 57 286

it is possible. The latter leads to a further advantage of the invention:

After a reversal of the direction of rotation of the rotor, those Wiegand wires which the have passed the neutral zone with the generation of a Wiegand pulse, but from the outer magnetic pole pairs have not yet been brought back into saturation when crossing the neutral zone again do not generate a Wiegand impulse, i.e. the rotor has when the direction of rotation is reversed, there is a certain dead angle that corresponds to the distance between the outer magnetic pole pairs of the neutral zone between the inner magnetic pole pairs depends, and this dead angle can in the invention Due to the more compact stator, the rotary encoder should be smaller than a comparable rotary encoder according to FIG DE-OS 21 57 286.

A cylinder geometry is preferably selected for the rotary encoder according to the invention (claim 2), i.e. the Wiegand wires should be parallel to each other on a cylinder surface with the rotor axis as the cylinder axis, e.g. in grooves on a cylindrical peripheral surface of the rotor and the magnetic poles should - with a coplanar or approximately coplanar orientation with respect to the rotor axis - lie as close as possible in front of this cylinder surface. But also in others Geometries, the invention can be implemented. So the Wiegand wires can be used instead of on a cylindrical surface Arrange on a conical surface parallel to the surface lines and match the arrangement of the magnet

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pole pairs on it so that the magnetic pole pairs lying next to each other in the direction of rotation to each of them closest surface line of the conical surface oriented parallel or approximately parallel are. A progressive enlargement of half the opening angle of the cone jacket up to 90 ° one to a corresponding disk geometry for the rotor, in which the Wiegand wires as well as them opposing magnetic pole pairs are oriented radially. As with a departure from the cylinder geometry the structure of the magnetic fields and their mutual influence and their mutual influence on the Wiegand wires are becoming increasingly confusing, the only thing you will notice in practice is the cylinder geometry deviate in exceptional cases.

As magnets, it is advantageous to use bar magnets, the length of which should not be greater than that of the Wiegand wires and which should be parallel or approximately parallel to the closest Wiegand wire.

The use of more than four magnetic pole pairs in the rotary encoder according to the invention while maintaining the asymmetrical excitation of the Wiegand wires is possible, although in any case not advantageous if it does so the blind spot of the rotor is increased.

An embodiment of the invention is shown schematically in the accompanying drawings.

Figure 1 shows the cross section LI qemäß Fiq. '* ■ by a rotary encoder,

Figure 2 shows the basic course of the magnetic Field strength to which each Wiegand wire is exposed during one revolution of the rotor, and

Figure 3 shows the along the line III-III in Fig. laid section through the rotary encoder.

The rotary encoder consists of a rotor 1 with a cylindrical outer surface 2, which is opposite a stator 3 at a small radial distance. The rotor 1 is made of aluminum or another non-magnetic material and is rotatable about the cylinder axis H. Equidistant grooves parallel to the axis 4 are incorporated into the outer surface 2 of the rotor 1, in each of which there is a Wiegand wire 5, which is embedded in synthetic resin, for example, and thereby fixed, just below the outer surface 2.

The surface of the stator 3 facing the rotor 1 is part of a cylinder jacket surface with the axis H as the cylinder axis. It doesn't have to be like that, it's important. that the stator 3 is as close as possible to the outer surface 2 of the rotor so that the magnetic influence of the Wiegand wires by the magnets 6, 7, 8 and 9 housed in the stator 3 is as intense as possible. It follows from this requirement that, in the case of small rotors, the shape of the stator corresponds more closely to the curvature of the rotor

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must than with large rotors, especially since the dimensions of the stator in the circumferential direction (λ of the rotor below dom Point of view of arranging the magnets 6 to 9 as close together as possible, mostly regardless of the 5- rotor diameter is.

The four magnets 6-9 are high-performance bar magnets, e.g. from cobalt samarium, which run parallel to the axis' [•. You are in the stator 1 in a passage Material that allows the flow of magnetic force, e.g. in a synthetic resin, embedded and lying close below the surface 10 of the stator, which faces the rotor 1. Between the two inner magnets 6 and 7 is on a ferromagnetic core 19, dessin Ends facing the rotor 1, an electrical winding 20, which typically has a few thousand turns, preferably parallel to the magnets 6 and 7 arranged.

The four magnets 6 to 9 are approximately equally strong, but arranged next to one another with alternating polarity. A Wiegand wire 5, which approaches the first outer magnet 8 when the rotor rotates in the direction of arrow 11, crosses its magnetic field, which is so strong that it aligns the hard jacket and the soft core in a corresponding orientation and saturates them magnetically able (at 1? in Fig. 2). Then the Wiegand wire b approaches the first inner magnet 6, which is oriented anti-parallel to the magnet 8. It follows that at point 13 the direction of the magnetic field is reversed. To the

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positive peak value 12 of the field strength is followed by a negative peak value 14, its absolute value because of the attenuation by the neighboring magnets 8 and 7 is less than the positive peak value 12, but is still sufficient to determine the direction of magnetization of the soft magnetic core of the Wiegand wire 5 to reverse, i.e. to reset the Wiegand wire magnetically (for which a field strength of 20 to 30 A / cm chooses).

Since the second inner magnet 7 is oriented antiparallel to the first inner magnet 6, the Wiegand wire traverses it 5 as the rotor 1 continues to rotate, a neutral zone again (spatial zero crossing of the field strength at point 15) and shortly after the zero crossing, namely at a field strength of approx. 8 A / cm, "ignites" the Wiegand wire 5, i.e. the soft magnetic core folds over again and orientates itself parallel to the hard magnetic shell. The associated short-term change in the magnetic flux is induced in the winding 20, which is also referred to as the sensor winding, an electrical voltage pulse - just the Wiegand pulse - which by means of a pulse processing circuit registered or otherwise processed. Near the second inner magnet 7 through — the Wiegand wire 5 again crosses a positive field strength peak value, the value of which corresponds to Absolute value of the previous negative peak value 14 approximately coincides. The positive peak 16 is not enough to put the Wiegand wire 5 high into the

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bring magnetic saturation as the first external magnet 8 does; but this is the field strength curve very steep on both sides of the zero crossing 15, so that the place at which the Wiegand wires 5 ignite, varies extremely little.

Since the second outer magnet 9 is antiparallel to the second inner magnet 7 is oriented, the Wiegand wire 5 traverses another coming from the magnet 7 Zero crossing 17 of the field strength and then a negative peak value 18 of the field strength, its absolute value coincides approximately with the peak value 12 and both the core and the shell of the Wiegand wire 5 can be folded down magnetically before after the completion of a rotor revolution in the magnetic field of the magnet 8, fold both the shell and the core of the Wiegand wire 5 over again. These two The latter total reorientation of the Wiegand wire is not used for signaling. she but could also be in windings, which would be arranged close to the outer magnets 8 and 9. Wiegand impulses induce, albeit weaker and less stable than in the central winding 20.

If the direction of rotation is reversed, those described will run. Operations the other way around and those in the winding 20 resulting voltage pulses have a corresponding reverse polarity and the point at which the respective Wiegand wire 5 ignites, - lies i.w. in the same small distance to the left (in the sense of Fig. 2) from the NuIl-

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passage 15 as in the first described direction of rotation to the right of this zero passage 15.

The dead angle of the encoder that becomes noticeable when the direction of rotation is reversed, in which none Wiegand pulses are received is at most the same the DrehwinkeidCt? between the mean zero crossing 15 and one of the outer magnets 8 and 9. In fact, the blind spot is smaller because a Wiegand wire, which had just ignited before reaching the peak value 18 (with direction of rotation according to arrow 11) or of the peak value 12 is saturated so far with the opposite direction of rotation by the magnet 9 or 8 that it can deliver a usable Wiegand pulse after reversing the direction of rotation.

Claims (3)

PATE N-TA N-VV / SjLTg '. ... - ww ν ** ^ w DR. HUDOLF SAUER Bfrp £ \ v | NG.'HELMUT HUBBUCH DfPL.-PHYS. ULRICH TWELMEIER WFSTLlCHE 2B - 31 (AM L EOPOLOPLAl / I D-7530 PFORZHEIM iwestmbm »«! ti ((I 11 3 I t HI 2? 90. '10 THLEOnAMMF PATMARK January 12, 1983 III / Be DODUCO KG Dr. Eugen Dürrwächter, 7530 Pforzheim "Inductive Rotary Encoder" .Patent claims Inductive rotary encoder, consisting of a rotor, which a sequence of Wiegand wires or the like. carries bistable elements, which are spaced next to each other on a surface of revolution, the axis of which is the axis of rotation of the rotor, and are arranged coplanar with the axis of rotation, and .from a neighboring surface of this revolution Stator with 'one electrical winding and with four coplanar or nearly coplanar with the axis of rotation of the Rotors and arranged at a distance next to each other in the direction of rotation, opposite the Wiegand wires Magnetic pole pairs, the static magnetic field of which moves past them when the rotor rotates Wiegand wires penetrated in their longitudinal direction and of which two closely adjacent pairs of magnetic poles are antiparallel oriented and arranged between the two other magnetic pole pairs, characterized in that for the purpose of asymmetrical excitation of the Wiegand wires (5) these the other two magnetic pole pairs (8,9) in turn to the inner magnetic pole pairs (6,7) adjacent to them. are oriented antiparallel. 2. Rotary encoder according to claim 1, characterized in that that the surface of revolution (2) a Cylinder surface is.
10 3. Rotary encoder according to claim 1 or 2, characterized in that the magnetic pole pairs (6 to 9) are formed by the ends of bar magnets which are parallel or approximately parallel to the straight Wiegand wires (5) adjacent to them . COPY