DE9004531U1 - Inductive position sensor - Google Patents

Description

PAPST-MOTORS .(JmbH;£ Cg. KG DE-907 G

7742 St. Georgen 20. 04. 1990

011-MH

Inductive position sensor 13:49 04/19/90

The invention relates to a sensor for detecting lengths or positions or for detecting angular positions. The basis of the measuring method is the influence of inductances with a ferromagnetic core or ferromagnetic magnetic circuit components by one or more magnets, preferably permanent magnets.

Methods of this type are known from e.g. EU-025 1785 A2 and DE- 27 52 880 Al and other publications, and allow a resolution of about 10 deg. el, which corresponds to a physical angular resolution of about 1 ... 2 deg.

corresponds.

The methods mentioned are relatively robust, as they are insensitive to contamination and can be used over a relatively wide temperature range. However, the angular resolution still leaves something to be desired, even when using special evaluation methods for precision measurements.

It is therefore an object of the present invention to provide a robust, cost-effective position or angle sensor with high resolution.

This problem is solved by the characterizing part of claim 1 and the remaining claims.

The basic idea of the invention is the realization that position determination using magnetically influenced inductances is not limited to

PAPST-MOTORS <s»bH '-■& Co KG DE-907 G

7742 St. Georgen 20. 04. 1990

011-MH

Inductances that are usually produced by winding a suitable ferromagnetic core or the combination of a wound coil and an associated ferromagnetic magnetic partial circuit, but instead of such inductances, a conductor track structure in the form of a meander can be used. This has the decisive advantage that the effective pole pitch of the sensor stator and rotor can now be kept about an order of magnitude smaller than was previously possible. At the same time, the manufacturing costs of such sensors can be reduced because the cost-critical winding of inductances is no longer necessary. In addition, the flat design of the sensor according to the invention also opens up the possibility of saving on construction volume. The production costs of the sensor according to the invention are also low because only a simple sheet is used for the ferromagnetic part of the inductance, which is preferably made of an amorphous metal. These materials are also called metallic glass, and are known under the trade names Vitrovac, Metglass, etc.

Details relating to the invention are described in detail using the drawings and the associated explanations.

It shows :

Fig. 1 a basic arrangement of conductor track, magnetic return and permanent magnet

PAPST-MOTOREN J3mbH: Sc CQ-KG. . _· DE-907 G 7742 St. Georgen 20. 04. 1990

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Fig. 3 two conductor tracks3JT 3 £ ¹¹ ^t pair of connecting terminals 2>f, It and ( S3 !>*»-) - The conductor tracks have a geometric phase offset from one another and each consist of two meander-shaped sections.

Fig. 4 a conductor track with an irregular meander structure for generating an index pulse to mark a reference position.

On the circuit board substrate 14 there are one or more meander-shaped conductor tracks 15, which are preferably applied using conventional printed technology, but can of course also be applied using known screen printing technology or can be applied as a wire in a likewise known manner, etc.

Below the conductor track(s) 15 there is a layer of appropriately selected thickness made of ferromagnetic material 19/, preferably one with high magnetic permeability and rather medium to low saturation behavior, e.g. the so-called mu-metal or amorphous metals, which are also referred to as metallic glasses and are known, for example, under the trade names Vitrovac and Metglass. Between the ferromagnetic layer and the conductor track there can also be an additional or alternative layer.

PAPST MOTORS .<§pibH & Co KG ~ DE-907 G

7742 St. Georgen 20. 04. 1990

011-MH

Insulating layer 18. The conductor track 15 is

powered via the connection/contact points 16 and 17,

preferably in pulses to create strong magnetic fields

through the conductor track without thermally overloading the conductor track material.

In the immediate vicinity of the conductor track there is a movable multi-pole magnet, preferably a permanent magnet, with at least one north pole 12 and one south pole 13. The magnetic field of this magnet extends through the conductor track to the ferromagnetic layer 19. Depending on the position of the poles above the conductor track and the direction of the current flow through it, a local saturation of the ferromagnetic layer 19 can be reached quickly or more slowly. This has a direct influence on the time constant of the current flow behavior of the conductor track and thus provides information about the position of the magnet with respect to a displacement in a plane that is parallel to the planes of the layers 14, 18, 19 mentioned.

In order to obtain a more precise position statement, it is useful to use more than one meandering conductor track. In particular, using three such conductor track arrangements, which have a phase offset from one another, a position statement can be made that is around 10 deg. el. or better and thus enables a resolution in the range of a few hundredths of a millimeter for standard conductor track dimensions. It is clear that the accuracy or reliability of the measurement can be further increased if a large number of such phase-shifted conductor tracks are used.

PAPST-MOTOREN GmbH &uacgr; Cc KG 7742 St. Georgen

DE-907 G

20. 04. 1990 Oil-MH

A space-saving arrangement for attaching several conductor tracks is shown in Fig. 2, with the contact points 21,22; 23,24; and 25,26.

In another arrangement according to Fig. 3, two phase-shifted meander structures are used, each of which is composed of two individual meander pieces and is supplied with current via the contacts 31, 32 and 33, 34 respectively.

become.

The magnetic field of the externally arranged magnet

is drawn superimposed and

can either strengthen or weaken the current-induced magnetic field, simultaneously for all north and south poles.

If a maximum effect is achieved in one conductor loop

present, no effect will be recorded due to the phase shift shown in Fig. 3, since the local premagnetizations caused by the permanent magnet cancel each other out on average.

When using additional conductor loops, instead of the phase shift of 180 deg. shown in Fig. 3, a phase shift of 360 deg. / η will have to be selected, where η is the number of conductor loops.

As can be seen from Fig. 3, a change in the inductance of the combination of conductor track and ferromagnetic layer occurs when, in one case, the conductor track is energized against the existing magnetic field and no or only delayed saturation of the ferromagnetic material is achieved, while in the other case, saturation is reached relatively quickly and a further increase in the current is essentially influenced by the air inductance of the conductor track. Depending on the position of the linearly or rotationally movable magnet, the

PAPST-MOTORS GmbH & Co KG 7742 St. Georgen

DE-907 G

20. 04. 1990 011-MH

assigned inductance of the conductor track can take on different values. It goes without saying that this behavior is current-dependent, however, and a certain minimum current must be provided to achieve the effect. Accordingly, in a simple version, one or more conductor tracks can only be supplied with unipolar current, which reduces the costs of the connected electronics. As a rule, however, bipolar current supply to the existing conductor track structures is advantageous.

The current supply and subsequent evaluation of the current flow is best carried out under the control of a microprocessor or controller, but can also be carried out in other ways. The task of such a computing unit is to use recorded measurement values of the current flow to determine the correct position of the movable magnet using a more or less complex pattern recognition or evaluation.

Since the position information repeats itself cyclically every 360 degrees, additional information for determining the absolute position of the sensor is advantageous.

This can be achieved, for example, by using several staggered sensors with different resolutions.

In another embodiment, an index pulse generator is used for this purpose, the mode of operation of which can be seen in Fig. 4: If the meander is given a varying length of the individual turns and the associated magnet has a corresponding local magnetization, the geometric configuration can be designed in such a way that only at a single, preferred position a more difficult or easier magnetization of the ferromagnetic material

PAPST MOTORS 'GlHbH "S CO-KG' -■ DE-907 G

7742 St. Georgen 20. 04. 1990

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is possible, in particular the ratio of the facilitated to the difficult current requirement for the saturation magnetization has an extreme value at this point.

Claims (1)

D-7742 St. Georgen 19. 06. 1990 G 90 04 531.9 ⁰ ^" ¹⁰¹ - 1 Claims : Sensor, in particular for rotary movements, with at least one variable inductance and with ferromagnetic magnetic circuit components, characterized in that that the inductance is made in the form of one or more meandering windings made of electrically conductive material, the size of the inductance is increased by flat ferromagnetic magnetic circuit components with a small layer thickness, the inductance is installed near or opposite a multi-pole permanent magnet and is energized during a rotary position measurement. Sensor according to claim 1, characterized in that the windings are made in the form of one or more meanders in the form of a printed circuit or meander-shaped wires. Sensor according to one or more of the preceding claims, characterized in that the ferromagnetic magnetic circuit components of the meandering inductance(s) consist of comparatively thin sheet metal. Sensor according to one or more of the preceding claims, characterized in that the essentially planar inductance(s) and planar magnetic circuit components as well as an intermediate insulating layer are laminated together are. PAPST-MOTORS GmbH & Co KG DE-907 G 7742 St. Georgen 19. 06. 1990 G 90 04 531.9 011-MH - z- Sensor according to one or more of the preceding claims, characterized in that/3 the distance between individual poles of a permanent magnet and the ferromagnetic material is chosen such that this material is pre-magnetized at least in individual places. Sensor according to one or more of the preceding claims, characterized in that Sheets with high magnetic permeability are used as material for the ferromagnetic magnetic circuit components, in particular iron/nickel-containing metals and so-called amorphous metals (also called metallic glasses). Sensor according to one or more of the preceding claims, characterized in that/3 the meandering shape of the inductance(s) extends linearly or is in the form of a circular arc. Sensor according to one or more of the preceding claims, characterized in that the inductance is composed of several components that have a meandering or linear shape. PAPST-MOTORS GmbH & Co KG DE-907 G 7742 St. Georgen 19. 06. 1990 G 90 04 531.9 011-MH Sensor according to one or more of the preceding claims, characterized in that/3 the meandering inductance(s) have one or more geometric phase offset(s). Sensor according to one or more of the preceding claims, characterized in that each of the inductors can be switched to either a positive power supply or a negative power supply via an electronic switch. Sensor according to one or more of the preceding claims, characterized in that/3 an index meander and an associated index magnetization is present Sensor according to one or more of the preceding claims, characterized in that/3 there are several sets of meander tracks that differ in the accuracy of the position resolution and that enable absolute position determination over a mechanical angle of rotation of 360 deg.