EP0839315A1

EP0839315A1 - Hall-effect contactless position sensor

Info

Publication number: EP0839315A1
Application number: EP97924082A
Authority: EP
Inventors: Jean-Christophe Guyot; Jean-Yves Frere
Original assignee: Airbus Group SAS
Current assignee: Aerospatiale Matra
Priority date: 1996-05-15
Filing date: 1997-05-13
Publication date: 1998-05-06
Also published as: JPH11509638A; WO1997043603A1; CA2227032A1; FR2748805A1; FR2748805B1; US6060880A

Abstract

A contactless position sensor including a Hall-effect cell (10) and a magnetic circuit consisting of a permanent magnet (18) and two pole pieces (20, 22). The magnet (18) and the cell (10) are arranged side by side between the pole pieces (20, 22), and said pole pieces comprise active surfaces (32, 34) at the opposite end from the cell relative to the magnet. This arrangement directly produces an output signal (Va-Vb) proportional to the distance (e) between the active surfaces (32, 34) and the target (38).

Description

CONTACTLESS POSITION SENSOR, HALL EFFECT.

DESCRIPTION

Technical area

The invention relates to a contactless position sensor using a Hall effect cell and a specific magnetic circuit making it possible to directly obtain an output signal whose value varies linearly with the distance separating the sensor from a magnetic target placed opposite of the last.

Such a sensor can be used for any non-contact distance measurement, as long as the target is made of a soft ferromagnetic material. Thus, this sensor is independent of the size of the target and can be used both when it is stationary and when it is in motion. The position sensor according to the invention therefore does not require any modification of the target whose position it is desired to know.

State of the art

There are many types of non-contact position sensors, which are based on different physical principles, among which mention may be made, only by way of examples, of optics, ultrasound, eddy currents, etc.

The choice of a particular sensor is generally made according to the nature of the material constituting the target and taking into account the particular conditions under which the measurement must be made, such as the dimensions of the target, its fixed or mobile nature. , space available, etc. The numerous contactless position sensors currently existing are either bulky devices or requiring a specific environment which makes them unsuitable for many applications (optical, ultrasonic sensors, etc.), or sensors which are not bulky but whose signal output must be subject to electronic processing later in order to be usable (eddy current sensors, etc.).

Statement of the invention

The subject of the invention is precisely a contactless position sensor whose original design allows it to present a reduced bulk and to deliver output signals directly proportional to the distance separating the sensor from the target.

According to the invention, this result is obtained by means of a contactless position sensor using a Hall effect cell and a specific magnetic circuit composed of a magnet and two pole pieces.

More specifically, a Hall effect position sensor is proposed in accordance with the invention, characterized in that it comprises a magnet and a Hall effect cell placed side by side between two pole pieces comprising, at the opposite of the Hall effect cell with respect to the magnet, active surfaces capable of being placed at a distance e from a target made of magnetic material, so that a magnetic flux created by the magnet either channeled by the pole pieces to be distributed, on the one hand, in the target and, on the other hand, through the cell to Hall effect and that the latter then directly delivers an output signal (Va-Vb) proportional to the distance e.

In a preferred embodiment of the invention, the magnet is a permanent magnet which delivers a constant magnetic field Ha oriented in a given direction, the active surfaces of the pole pieces being placed in the extension of one of the other and oriented parallel to this direction, and the Hall effect cell being oriented so as to detect a magnetic induction B oriented parallel to said direction.

In the preferred embodiment of the invention, the pole pieces have two planar and parallel faces opposite, in contact with two opposite faces, planar and parallel, of the magnet and spaced apart by the same spacing L with respect to two opposite, plane and parallel faces of the Hall effect cell. The relationship :

Sa + Sec ,, Sent «——

L 2e is then satisfied, Sa, Sec and Sent designating the respective sections of the magnet, of the effect cell

Hall and air gap separating the active surfaces from the target. Preferably, the active surfaces of the pole pieces have shapes complementary to those of a surface facing the target. These active surfaces can thus be flat surfaces or concave cylindrical surfaces, depending on whether the surface facing the target is itself plane or cylindrical.

According to specific provisions and solely by way of example, the sensor can present ter a circular or rectangular section in a plane parallel to the direction of the magnetic field delivered by the permanent magnet.

Brief description of the drawings

We will now describe, by way of nonlimiting examples, various preferred embodiments of the invention, with reference to the appended drawings, in which:

- Figure 1 is a perspective view schematically showing a Hall effect cell;

- Figure 2 is a curve which represents the characteristic Va - Vb = f (B) of a Hall effect cell, for different values of the bias current i. crossing it;

- Figure 3 is a sectional view schematically showing a Hall effect position sensor according to the invention; - Figure 4 is a view showing the magnetic circuit of the sensor of Figure 3;

- Figure 5 is a view showing the simplified magnetic diagram of the sensor according to the invention; - Figure 6 is a perspective view of a first embodiment of the Hall effect position sensor according to the invention;

- Figure 7 is a perspective view showing another embodiment of the Hall effect position sensor; and

- Figure 8 is a top view illus¬ trant a third embodiment of the Hall effect position sensor according to the invention. Detailed presentation of different embodiments

With reference to FIG. 1, it is recalled that a Hall effect cell consists of a parallelepiped plate 10 of an electrically conductive material, crossed in the direction of its length by a bias current i_ and placed in a field magnetic induction B which crosses the plate in the direction of its thickness. Under these conditions, the Hall effect consists of the appearance of a potential difference (Va - Vb), called Hall voltage, between the opposite faces of the plate. This Hall voltage is proportional to the magnetic induction B and to the bias current i_ which passes through it. We can therefore write:

Va - Vb = k.i.B (1),

where k represents the Hall constant of the cell. In practice, the plate 10 has at its ends two opposite connections allowing it to be connected to a current source which delivers the bias current i_ passing through the plate. The plate 10 also has on its faces two other opposite connections serving to connect it to a voltage measuring device such as a voltmeter, which measures the Hall voltage (Va - Vb).

As illustrated in FIG. 2 and in accordance with relation (1), the characteristic of a Hall effect cell, ie the curve giving the Hall voltage (Va - Vb) as a function of the magnetic induction B, can be modified at will by varying the bias current i. So, we FIG. 2 shows the characteristics of the same Hall effect cell for values of the bias current progressively increasing from a value iΛ to a value .i4. After this reminder, a Hall effect position sensor according to the invention will now be described with reference to FIG. 3.

As already indicated before, such a sensor essentially consists of a Hall effect cell and a specific magnetic circuit whose original design allows direct output signals to be obtained which vary linearly in function. the distance from the sensor to the target.

More precisely, a Hall effect cell 10 is recognized in FIG. 3 such as that the principle of which has just been recalled with reference to FIG. 1. The reference 12 designates the different electrical conductors by which this cell 10 is connected to the current source (not shown) allowing it to apply the bias current i_, for example in a direction perpendicular to the plane of the figure, as well as to the apparatus, (not shown) used to measure the Hall voltage (Va - Vb) between the planar faces 14 and 16, parallel and opposite, of cell 10.

The magnetic circuit associated with this Hall effect cell comprises a permanent magnet 18 and two pole pieces 20 and 22 made of a magnetic material. More specifically, the permanent magnet 18 is a magnet of parallelepiped shape which delivers a constant magnetic field Ha between two planar faces 24 and 26 parallel and opposite, the spacing of which defines the thickness of the permanent magnet 18.

As illustrated in FIG. 3, the Hall effect cell 10 and the permanent magnet 18 are arranged side by side and slightly apart from one another. In addition, the cell 10 and the permanent magnet 18 present a common plane of symmetry, so that the faces 14 and 16 of the cell 10 as well as the faces 24 and 26 of the permanent magnet 18 are parallel between they. It can also be seen in FIG. 3 that the thickness of the Hall effect cell 10 is substantially less than that of the permanent magnet 18.

The pole pieces 20 and 22 are placed on either side of the permanent magnet 18, so as to be supported respectively against the faces 24 and 26 of the latter by planar faces opposite 28 and 30 As will be seen in more detail below, the pole pieces 20 and 22 may moreover have different geometries without departing from the scope of the invention.

By observing FIG. 3, it can be seen that the pole pieces 20 and 22 extend beyond the permanent magnet 18 in a direction opposite to the cell 10 relative to this magnet, to end with surfaces active 32 and 34. These active surfaces 32 and 34 constitute the detection part of the position sensor according to the invention, therefore, the use of the sensor results in placing these surfaces 32 and 34 in front of a surface 36 of a target 38 whose position is desired.

More specifically, the active surfaces 32 and 34 of the pole pieces 20 and 22 are placed in the extension of one another and they are oriented tees parallel to the direction of the magnetic field Ha delivered by the permanent magnet 18. As will be seen below, these surfaces 32 and 34 preferably have a shape complementary to that of the surface 36 of the target 38. This characteristic makes it possible to have a substantially uniform distance or spacing e_ between the active surfaces 32 and 34 of the pole pieces and the surface 36 of the target 38.

Opposite these active surfaces 32 and 34 relative to the permanent magnet 18, the polar pieces 20 and 22 have extensions 20a, 22a, the dimensioning of which is such that the Hall effect cell 10 is placed in all between the flat faces 28 and 30 of the pole pieces 20 and 32. In view of the relative dimensions of the cell 10 and of the magnet 18 mentioned previously, the faces 14 and 16 of the cell 10 are separated from the respective faces 28 and 30 of the pole pieces 20 and 22 by the same ecarte¬ ment. As illustrated schematically in dotted lines in FIG. 3, the magnetic flux created by the magnet 18 is channeled by the pole pieces 20 and 22 and is distributed on one side in the target 38 and on the other through cell 10 forming the Hall effect probe, in the form of a leakage flow. The magnetic flux which crosses the cell is designated by the reference φ l and that which crosses the target is designated by the reference φ 2.

The amount of flux φ 2 which passes through the target 38 depends on the distance e between the active surfaces 32, 34 of the sensor and the surface 36 of the target. The more this distance e decreases, the more the flux φ 2 increases lie, and vice versa. Since the total magnetic flux created by the permanent magnet 18 is constant and equal to the sum of the fluxes φ l and φl, the variations in the flux φ 2 depending on the distance e_ result in inverse variations in the flux φ l which crosses Hall effect cell 10.

In addition, the magnetic flux φ l which crosses the Hall effect cell and the magnetic induction B in which this cell is placed are connected by the relation:

φ l ≈ B.Scel (2),

where Scel designates the cross section of the magnetic flux φ l, that is to say the section of the cell 10 parallel to the faces 14 and 16.

The section S being constant, the magnetic induction B in which the effect cell is located

Hall is directly proportional to the magnetic flux φ l and, therefore, inversely proportional to the magnetic flux φ 2.

The relation linking the distance e_ to the flux φ l which crosses the Hall effect cell is given by the equations representative of the magnetic circuit formed by the sensor illustrated in FIG. 3. This magnetic circuit is represented in detail in FIG. 4. More precisely , in the latter figure, the reference Ra designates the reluctance of the magnet, while the references Rc and R'c designate the reluctance of the pole pieces 20 and 22, respectively on the side of the target 38 and on the side of the Hall effect cell. The reluctance of the target is designated by the reference Rcible, while the reluctance equivalents due respectively to the sensor / target air gap and to the air gap between the pole pieces on the side of the Hall effect cell are designated respectively by the references Re and Rec. Finally, the reference Ha. This represents the equivalent electromotive force of the permanent magnet 18, Ha corresponding to the magnetic field created by the magnet at its operating point, while La denotes the thickness of the magnet between its faces 24 and 26.

In the magnetic circuit of FIG. 4, the reluctances Rc, R'c and Rcible of the magnetic parts are negligible compared to those of the air gaps. Consequently, the magnetic circuit of FIG. 4 can be reduced to the simplified circuit of FIG. 5, in which only the reluctance Ra of the magnet remains, and the equivalent reluctances Re and Rec corresponding respectively to the sensor / target air gap and at the air gap of the Hall effect cell.

The flow equation from this simplified diagram leads to the relationship:

2Re φ \ = -.Ha. The (3)

2 Re (Rα + Rec) + Rα.Rec

Given this relation (3) and the relation (2) which connects the flux φ l to the magnetic induction B which crosses the Hall cell, the relation (1) giving the Hall voltage becomes:

Furthermore, if we designate by μ _e nt l ^fl permeability of the sensor / target air gap and by Sent the section of this air gap, the equivalent reluctance Re due to the sensor / target air gap is related to the distance e by the relationship :

Re = -.e (5) μ _ent Sent

Taking this relation (5) into account in relation (4) leads to the following equation:

k.i. Ha. the e

Go-Vb =. (6).

Seal _, „_ _{, r} , _ _ _N. [i _ent . Sent. Ra. Rec e (Ra + Rec) + μ

By posing k.i. Ha. the

/ Cl =

Seal

μ _ent Sent.Ra.Kec

Λ2 =, and

2

equation (6) becomes:

Go-Vb≈Kl (7). e.K3 + K2 By choosing the dimensions and the materials so that e, K3 is negligible compared to K2, this relation (7) becomes:

K \ Va - Vb = - .e (8)

K2

Consequently, the output signal of the sensor constituted by the Hall voltage (Va - Vb) is therefore directly proportional to the distance e which separates the sensor from the target.

If we apply relations of the type of relation (5) to the reluctance Ra of the magnet and to the equivalent reluctance Rec of the air gap corresponding to the Hall effect cell, the condition of linearity requires that e.K3 or negligible before K2 is written:

Pa-Sa ₊ μ _e c.-Sec _{<< ζ} μe _nt .Sent

(9),

The Lee 2nd

with μ _a and μ _ec which respectively designate the permeability of the magnet and the air gap on the side of the Hall effect cell, Sa and Sec which respectively designate the sections of the magnet and of the Hall effect cell, Lee designating the thickness of the air gap corresponding to the Hall effect cell.

If the materials are chosen so that the permeabilities μ _a , μ _ec and μ _e nt are substantially equal, as well as the thicknesses La and Lee which are then designated by the letter L, the relation ( 9) becomes: Sa + Sec «Sent

(10)

There

The linearity condition of the response of the sensor according to the invention is therefore satisfied as soon as the distance e to be measured remains small enough for the condition fixed by relation (10) to be satisfied. It should be noted that the choice of the geometry of the sensor makes it possible to preserve this condition up to relatively large values of the distance e_.

Consequently, it can be seen that a Hall effect position sensor conforming to the diagram in FIG. 3 constitutes a device of reduced size, usable industrially, and which directly supplies an output signal proportional to the distance to be measured, without that it is necessary to add to it any processing circuit.

Figures 6 to 8 illustrate by way of example three possible embodiments of the sensor according to the invention.

In the case of FIG. 6, the sensor has a circular section along a plane parallel to the direction of the magnetic field Ha and perpendicular to the plane of FIG. 3. In this case, the outer surfaces of the pole pieces 20 and 22 are located on the same cylindrical surface. It can also be seen in FIG. 6 that the cohesion of the sensor is ensured by an electrically insulating material 40 such as a resin, in which the magnet 18, the cell 10 and the pole pieces 20 and 22 are embedded.

In the embodiment illustrated in FIG. 6, the active surfaces of the pole pieces 20 and 22 are planar surfaces located in the same plane intended to face the target 38.

In another exemplary embodiment shown in FIG. 7, the sensor has a rectangular section along a plane parallel to the direction of the magnetic field Ha and perpendicular to the plane of FIG. 3. In this case, the external surfaces of the pole pieces 20 and 22 are parallel to the opposite faces 28 and 30 thereof. Here again, a material 40 such as a resin ensures the cohesion of the different sensor parts and the active surfaces of the pole pieces are located in the same plane.

Finally, there is shown in FIG. 8 another embodiment of a sensor according to the invention, applied to the case where the target 38 is a rotating cylindrical part. As can be seen, the active surfaces 32 and 34 of the pole pieces 20 and 22 are then concave cylindrical surfaces complementary to the peripheral surface of the target 38. The parts of the pole pieces closest to the target then have the shape of hooves. The measurement carried out is thus distributed over an angular sector, which makes it possible to integrate any faults that may be present on the periphery of the target 38 and to greatly reduce the errors in the signal delivered.

Of course, the embodiments which have just been briefly described with reference to Figures 6 to 8 are given only by way of examples. Indeed, it will be readily understood that other geometries can be envisaged either to take account of the shape of the target, or to take account of the space available.

Claims

1. Hall effect position sensor, charac¬ terized in that it comprises a magnet (18) and a Hall effect cell (10) placed side by side between two pole pieces (20,22) comprising, at the opposite the cell to the Hall effect with respect to the magnet, active surfaces (32, 34) able to be placed at a distance e from a target (38) made of magnetic material, such so that a magnetic flux created by the magnet (18) is channeled by the pole pieces (20,22) to be distributed, on the one hand, in the target (38) and, on the other hand, through the Hall effect cell (10) and that the latter then directly delivers an output signal (Va-Vb) proportional to the distance e.

2. Sensor according to claim 1, charac¬ terized in that the magnet (18) is a permanent magnet which delivers a constant magnetic field Ha oriented in a given direction, the active surfaces (32,34) pole pieces (20, 22) being placed in the extension of one another and oriented parallel to this direction, and the Hall effect cell (10) being oriented so as to detect a magnetic induction B oriented parallel to said direction.

3. Sensor according to any one of the preceding claims, characterized in that the pole pieces (20,22) have two plane and parallel faces opposite, in contact with two opposite faces (24,26), planes and parallels, of the magnet (18), and spaced by the same spacing L with respect to two opposite faces (14,16), planes and para- lèles, of the Hall effect cell (10), in which the relation:

Sa + Sec Sent L 2e is satisfied, Sa, Sec and Sent designating the respective sections of the magnet (18), of the Hall effect cell (10) and of the air gap separating the active surfaces (32,34) from the target (38).

4. Sensor according to any one of the preceding claims, characterized in that the active surfaces (32,34) of the pole pieces (20,22) have shapes complementary to those of a surface facing the target (38 ).

5. Sensor according to any one of the preceding claims, characterized in that the active surfaces (32,34) of the pole pieces (20,22) are planar.

6. Sensor according to any one of claims 1 to 4, characterized in that the active surfaces (32,34) of the pole pieces (20,22) are concave cylindrical surfaces.

7. Sensor according to any one of the preceding claims, characterized in that it has a circular section along a plane parallel to said direction.

8. Sensor according to any one of claims 1 to 6, characterized in that it has a rectangular section along a plane parallel to said direction.

9. Sensor according to any one of the preceding claims, characterized in that the Hall effect cell (10), the magnet (18) and the pole pieces (20, 22) are embedded in a resin (40 ).