GB2150366A - Pulse generator with magnetic polarisation reversal - Google Patents

Abstract

A pulse generator is described in which electric signals are induced, by reversal of magnetisation of a Wiegand wire (6), in a pick-up coil (7) which coaxially encloses the Wiegand wire (6) and in which the reversal of magnetisation is effected at the Wiegand wire (6) by the close relative movement of a plurality of magnetic poles (10, 11) with differing polarity. The Wiegand wire (6) is oriented relative to the magnetic poles (10, 11), which are being moved past it, in such a manner that one of its two ends is exposed to the magnetic field of these magnetic poles (10, 11) to a greater extent than the other end. For compensating the signal induced, additionally to the Wiegand signal, in the pick-up coil (7) by the magnetic poles (10, 11), a compensating coil (12) is provided which coaxially surrounds the Wiegand wire (6), is connected in series with the pick-up coil (7) and is exposed to the magnetic field of the magnetic poles (10, 11) in the vicinity of the pick-up coil (7) in a winding direction which is opposite to that of the pick-up coil (7). An optional guide plate (8) is used for signal amplification in coils (7) and (12). In the embodiment of Figure 2a the poles (10, 11) are mounted on a rotor (2), but a linearly moving pole arrangement may be used also. <IMAGE>

Description

SPECIFICATION Magnetic transmitter of jumps in polarisation Prior art The invention relates to a magnetic transmitter of jumps in polarisation of the generic type claimed in the main claim.

A magnetic transmitter of jumps in polarisation of this type is already known from German Offenlegungsschrift 3,140,302. This transmitter has the disadvantage that, as a result of the magnetic poles moving past the pick-up coil, a conventional induced signal is generated in this coil, in addition to the Wiegand signal, the amplitude of which increases with increasing relative velocity between the magnetic poles and the Wiegand wire and causes interference during the further processing of the output signal.

From German Offenlegungsschrift 2,654,755 and from the corresponding U.S. Patent 4,150,314 a magnetic transmitter of jumps in polarisation is also known in which, as a result of the reversal of magnetisation in a Wiegand wire, electric signals are induced in a pick-up coil by moving a plurality of magnetic poles with differing polarity past the Wiegand wire. In this arrangement, the conventional induced signal, which is generated in the pick-up coil additionally to the Wiegand signal also in this case, is compensated by a compensating coil which is coaxially enclosed by the pick-up coil.

In this arrangement, however, the Wiegand wire is arranged outside the common axis of the two coils and clamped between the windings of these coils so that the sensor arrangement is unsymmetrical.

The consequence of this is that, although the conventional induced signal caused by the magnetic poles moving past is removed from the signal obtained, this latter signal is sensitive to the coils being twisted around their common axis which produces problems during the assembly of the sensor arrangement and requires considerable adjusting work. In addition, problems occur in the resolution of the signals when the magnetic poles of differing polarity are moved past the Wiegand wire at a small distance, which is of disadvantage in many cases of application, particularly in the motor vehicle, where the magnetic poles are preferably arranged on a rotating disc.

Advantages of the invention In comparison, the magnetic transmitter of jumps in polarisation according to the invention, having the characterising features of the main claim, has the advantage that the conventional induced signal generated in the pick-up coil additionally to the Wiegand signal is compensated by the compensating coil without the output signal obtained being sensitive to twisting of the two coils around their common axis so that the assembly of the sensor arrangement is simplified and the range of applications is expanded. Claim 2 has the further advantage that the pulses induced in the pickup coil are amplified. The features of Claim 3 make it possible to reduce the number of turns of the compensating coil which reduces the dimensions of the sensor arrangement.

Drawing An illustrative embodiment of the invention is explained in greater detail in the description which follows and shown in the drawing, in which: Figures la, b and c show the top view, section and detail of a magnetic transmitter of jumps in polarisation (angle and revolution transmitter) known from German Offenlegungsschrift 3,140,302, Figure id shows the output signal picked up at the ends of the winding of the pick-up coil according to Figures la, b and c, Figure 2a shows a diagrammatic representation of an illustrative embodiment of a magnetic transmitter of jumps in polarisation according to the invention, and Figure 2b shows the signal picked up at the outer ends of the series circuit consisting of pickup coil and compensating coil in the illustrative embodiment of Figure 2a.

Description of the illustrative embodiments In Figures la, band c, a transmitter of jumps in polarisation is shown which can be used for measuring revolutions, particularly for measuring especially low revolutions such as are required, for example, in anti-locking braking systems when the vehicle wheels have almost reached standstill or the locking condition. On a shaft 1, a rotor 2 is mounted fixedly which is provided with a toroidal permanent magnet 3. The permanent magnet 3 is associated with polarisation guide plates 4 which are provided with a plurality of claw poles 5, for example 100 claw poles. The claw poles 5 are magnetised via the polarisation guide plates 4 in such a manner that adjacent claw poles 5 have differing magnetic poles.In this arrangement, the claw poles 5 overlap in the axial direction of the rotor as can be seen in Figure ib. This produces a field pattern which is homogeneous in the axial direction and curved in the plane of the rotor 2. The curvature of the field pattern in the plane of the rotor 2 can be seen in Figure ic.

Opposite to the claw poles, a Wiegand wire 6 surrounded by a pick-up coil 7 is located radially with respect to the rotor 2 and mounted fixedly on a stator, not shown. At its end facing the rotor 2, the Wiegand wire 6 penetrates a strip-shaped or circular guide plate 8.

As can be seen from Figure Ic, the adjacent claw poles 5, 5' the outward-pointing ends of which have differing polarities, generate a magnetic field which is sharply curved in the plane of the rotor 2.

When the rotor 2 rotates, the claw poles 5, therefore, generate at the location, shown in Figure ic by a dot-dashed line, of the guide plate 8 a magnetic field which alternates in its intensity and direction. This is because, whilst the guide plate 8 is predominantly exposed to a magnetic field component which is radially oriented with respect to the rotor axis in the immediate vicinity of a claw pole 5, 5', it is predominantly exposed to a tangential magnetic field componet, acting radially on the Wiegand wire 6, between the claw poles 5, 5'.

Physically, this produces, between the claw poles 5, 5', Bloch wall detachments in the wire 6 in the area surrounded by the guide plate 8. As the wire 6 and the guide plate 8 continue to move relative to the claw poles 5, 5', the field lines emerging radially from the claw poles 5, 5' and acting via the guide plate 8 in an axial direction (with respect to the wire axis) on the wire 6 then predominate. This component, which acts axially in the wire 6, now results in the Bloch walls being moved so that the effect of magnetisation reversal has a progressive effect over the length of the wire. In this connection, it must be noted that the major magnetic action in this respect is produced by the piece surrounded by the guide plate 8 of the wire 6, producing a very precise time dependence of the magnetisation reversal process on the relative movement between rotor 2 and wire 6.

In this arrangement, the guide plate 8 is used only for amplifying the pulses induced in the pickup coil 7. In principle, therefore, the arrangement described is capable of operating also without the guide plate 8.

In Figure 2a, an illustrative embodiment constructed in accordance with the invention is shown which is preferably used for measuring low revolutions, according to the illustrative embodiment of Figures 1a, b and c. Deviating from the illustrative embodiment of Figures 1a, b and c, the magnetic poles in the illustrative embodiment of Figure 2a are formed by magnets 10, 11 which are preferably permanent magnets and which are distributed over the periphery of the rotor 2. They consist of individual magnets or of magnetic strips, which are remagnetised with several poles, preferably permanent magnets bonded with plastic.

The magnetic transmitter of jumps in polarisation according to the invention of Figure 2a differs from that of Figures 1a, b and c in that, for compensating the signal induced additionally to the Wiegand signal in the pick-up coil 7 by the magnetic poles, a compensating coil 12 is provided which coaxially surrounds the Wiegand wire 6. The compensating coil 12 is connected in series with the pick-up coil 7 in a manner not shown in the drawing and is exposed to the magnetic field of the magnets 10, 11 with a winding direction which is opposite to that of the pick-up coil. As can be seen from Figure 2a, the compensating coil 12 is wound onto the guide plate 8. In the area outside the guide plate 8, the Wiegand wire 6 is sheathed by a small protective tube 13 of glass.

In Figure 2b, the signal picked up at the outer ends of the series circuit consisting of pick-up coil 7 and compensating coil 12 in the illustrative embodiment of Figure 2a is shown. It can be clearly seen that the sinusoidal component of the signal shown in Figure 1d is eliminated by the action of the compensating coil 12.

In the arrangement according to the invention, shown in Figure 2a, the guide plate 8 is used for amplifying the signals induced in the pick-up coil 7 and in the compensating coil 12. In principle, therefore, the arrangement described is capable of operating also without the guide plate 8.

In addition, it is important to note that the arrangement described with the aid of Figure 2a, comprising stator and rotor, is intended merely as an example. Naturally, the arrangement according to the invention can also be used in arrangements in which magnetic poles and wire perform a different form of movement or approach with respect to each other, for example in linear form. Furthermore, instead of an arrangement 6,7,12,8; 10,11, several arrangements can also be used for obtaining pulses which are offset in time or several arrangements of magnetic poles can act on a pick-up element which is provided with a compensating coil.

A known soft magnetic material, for example iron or soft ferrite, can be used as the material for the guide plate 8.

Claims (4)

1. Magnetic transmitter of jumps in polarisation in which electric signals are induced by reversal of magnetisation in a Wiegand wire (6) in at least one pick-up coil (7) which coaxially surrounds the Wiegand wire (6) and in which transmitter the reversal of magnetisation is caused at the Wiegand wire (6) by the close relative movement of a plurality of magnetic poles (10, 11) having differing polarities, the Wiegand wire (6) being oriented relative to the magnetic poles (10, 11), which are being moved past it, in such a manner that one of its two ends is exposed to a greater extent than the other end to the magnetic field of these magnetic poles (10, 11), characterised in that, for compensating the signal induced, additionally to the Wiegand signal, in the pick-up coil (7) by the magnetic poles (10, 11), a compensating coil (12) is provided which also coaxially surrounds the Wiegand wire (6) and is connected in series with the pick-up coil (7) and which is exposed to the magnetic field of the magnetic poles (10, 11) in the vicinity of the pick-up coil (7) with the opposite direction of winding.

2. Transmitter of jumps in polarisation according to Claim 1, characterised in that the Wiegand wire (6), at its end which is exposed to a greater extent to the magnetic field, is provided with a guide plate (8) which is penetrated by the Wiegand wire (6).

3. Transmitter of jumps in polarisation according to Claim 2, characterised in that the compensating coil (12) encloses the guide plate (8).

4. A magnetic transmitter of jumps in polarisation substantially as herein described with reference to Figures 2a and 2b of the accompanying drawings.