DE9105145U1 - Position sensor for rotary movements - Google Patents

Description

PAPST-MOTOREN GmbH & Co KG ':;&Ogr;&Egr;
D-7742 St. Georgen 22 April 1991

011-MH

Description

The invention relates to a position sensor for detecting
linear or rotary movements with high resolution.

A typical application for sensors of this type
consists in determining the rotor position or angular position of a
electric motor. In another application, for example, it is necessary to determine the rotational position of a valve or throttle valve.

Another typical application is to convert manually executed movements into a computer-compatible input signal.

For the above applications, sensors are preferably used which consist of one or more light barriers
which are operated by a movable, slotted disc.

When such discs rotate around a given axis, it is therefore possible to use the light barrier to
to emit an electrical signal which signals the rotational position of a disk through different heights or intensity.

Such sensors are available in a variety of designs
However, they must be protected from dust
and contamination. High-resolution sensors require relatively finely structured disks, which have a strong influence on the cost of such a sensor.

PAPST-MOTOREN GmbH & Co KG .--,-. \-r '" , 0E■?300f /-G _c ■; _c D-7742 St. Georgen 22 April 1991

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It is therefore an object of the present invention to provide a robust sensor that is insensitive to dust and contamination, has a high resolution and is characterized by particularly low manufacturing costs.

This object is achieved by the characterizing part of the main claim, in particular by an embodiment according to subclaim 10.

Further developments of the invention emerge from the further subclaims, the description and the figures.

It shows:

Fig.1

a sensor according to the invention with 6 individual coils, which periodically change their inductance characteristics due to the rotational position of a rotor part 7

Fig.2

the block diagram of an associated oscillator and evaluation electronics 2 0

Fig.3

the function of a constant 3 3 with a superimposed sine term 3 shown in Cartesian (Fig. 3B) and polar coordinates (Fig. 3 A)

Fig. 4 A, 4 B, 4 C, 4 D

different shapes of single coils 40, 48 and 49

PAPST-MOTOREN GmbH & Co KG %-".J ..,0&Ggr;-300&Iacgr; *3g J ₃ D-7742 St. Georgen 22. April 1991

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Fig. 5 is a block diagram of an oscillator stage 50 for coils according to Fig. 1 or

Fig. 6 the variable course of the inductances of individual coils according to Fig. 1 or 4 over the angle of rotation of a rotor part according to Fig.

Fig. 7 shows a construction for analyzing the rotor position of a rotor part 7 and representation of a representative phase angle θ (theta) which represents a position of such a rotor part.

Fig. 8 a shape for a rotor part consisting of a ferromagnetic part and a metallic, diamagnetic part

Fig. 9 the exact contour of a two-bladed rotor part in the form of a general conchoid

Fig.

an exact contour similar to Fig. 9 with almost straight side parts

PAPST-MOTOREN GmbH & Co KG ; ,"/ --,,OE D-7742 St. Georgen 22 April 1991

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Fig. 11 an exact contour in the form of a conchoid, with only one wing

Fig. 12 an arrangement with three coils, which have an angular extension of 90 deg. mech. and are evenly distributed over the angle of 360 deg.

PAPST-MOTOREN GmbH & Co KG , ■,," \. " DE^-3OC-^f G--D-7742 St. Georgen April 22, 1991

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The invention enables the cost-effective construction of rotary sensors by combining several different individual measures, of which the following are known in isolation:

Coil design in the form of a printed circuit

Determination of the inductance of individual coils by arranging them in an oscillator circuit and measuring the oscillation frequencies

- Evaluation of more than two measured values by interpolation or pattern analysis, preferably by means of a Fourier analysis or transformation

Another measure, which is not yet known, consists in achieving a special type of change in the inductance characteristics or the oscillator frequencies over the angle of rotation of the rotating part by means of a suitable shape of the coils and the influencing rotating part (rotor part of the sensor).

This change or variation consists of a periodic, sinusoidal function and is characterized by the smallest possible proportion of harmonics.

In other words, this means that the inductance has a constant base value and, due to the rotor movement, has a superimposed ripple that has the shape of a sine function.

PAPST-MOTORS GmbH & Co KG D-7742 St. Georgen

DE-30G1 G " ^x '"■'■ 22 April 1991 011-MH

Such a measure has the advantageous effect that a relatively accurate extrapolation of the rotor position is possible from, for example, three measured values obtained simultaneously, so that the use of correction tables or functions is either unnecessary or at most has to be used to calculate particularly accurate position values.

In simpler embodiments of the invention, a special shape of coils and/or rotor parts can be dispensed with, but in this case the use of the aforementioned correction tables or functions is necessary to increase the measurement accuracy.

Fig. 1 shows a complete sensor, but without the associated electronics.

On a base plate 1 there are several, but at least 3 different coils or coil sets.

These coils can be made using printed circuit board technology, as shown in Fig. 1, for example, but they can also be wound, e.g. using the well-known baked enamel wire technology.

Fig. 1 shows six individual coils, three of which are marked with the reference numbers 2, 3 and 6.

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D-7742 St. Georgen 22 April 1991

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It is useful to connect two diametrically opposite coils in series so that the inductance is twice as large.

In this way, there are three coil groups of two individual coils each in Fig. 1. The advantage of this measure is that various error influences, such as incorrect alignment between the axis of rotation and the center of the coil arrangement on the base plate, are already compensated to a certain extent.

Above the base plate 1 with the coil arrangement there is a rotor part 7 which can be rotated by means of or around a rotation axis. The angle of rotation around the axis is designated (phi) and can be more than 3 60 deg. mech.

In the simplest case, the rotor part 7 consists of a piece of iron sheet. It preferably has a special edge or contour 8.

If required, it is provided with radial slots which reduce the formation of eddy currents, provided that the rotor part 7 consists of a piece of sheet metal.

Alternatively, the rotor part can also consist of a ferrite part or a copper sheet. It is of course also possible to provide a layered construction consisting of a plastic carrier and a relatively thin sheet metal part, especially if highly permeable sheets are provided as an effective component for the rotor part 7. Such sheets are then attached to one of the end faces 11 of the rotor part.

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D-7742 St. Georgen 22 April 1991

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When designing the sensor, it is important that the rotor part and the coil set have a different symmetry, i.e. that e.g. the rotor part has one, two, four or eight etc. axes of symmetry while the coil arrangement has an odd-numbered symmetry, i.e. multiples of 3, 5, 7, etc. coils are present or vice versa.

In this way, a different periodicity is created between the periphery of the rotor part and the coil arrangement, which is advantageous for the analysis of the individual inductance values of the coils or coil groups.

Fig. 2 shows a block diagram of the evaluation electronics associated with the sensor. The coils or coil groups of the sensor are designated L1, L2, L3. Other sensor designs according to the invention use additional inductances, e.g. five, six, seven, etc. coils or coil sets.

The coils or inductance values Ll, L2, L3 work separately with associated oscillator stages 21, 22 and 23, respectively, which output output signals fl, f2 and f3 etc. to the evaluation unit 20, whereby the output signals have comparably large but noticeably different frequencies. The frequency differences are typically a few percent based on an average or characteristic frequency value of these output signals and are dependent on the position of the rotor part 7. The evaluation unit expediently consists of an electronic circuit, in particular a microprocessor circuit, and in particular has at least one frequency measuring stage 24 for determining the different frequencies of the signals fl, f2, f3.

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This is preferably done using one or more timers/counter units (counter/timer), as they are already built into many microprocessor components.

Furthermore, the evaluation unit 20 has an analyzer stage which uses the determined frequency values of the signals fl, f2, f3 to carry out a pattern analysis of these frequency values and, in the simplest case, uses a so-called discrete Fourier transformation (DFT) for this purpose.

The evaluation unit 20 forwards measured values determined or analyzed in this way to a digital or analog display 26 or to a higher-level computer or controller 27, which in a preferred application controls the energization of a motor with electrical energy, compressed air, etc.

Fig. 3 shows a preferred embodiment for the edge or contour of a rotor part 7 according to the invention.

In order to reduce the harmonics mentioned above, it is important that the contour of the rotor part is matched to the shape or contour of the coils. A particularly advantageous embodiment is obtained if the contour of the rotor part is designed in the form of a general conchoid and is therefore defined in polar coordinates according to a formula r = a + b*cos(c*phi), where r indicates a ray of travel that extends from the center of rotation of the rotor part. The angle phi extends between r and a predefined basic position.

PAPST-MOTORS GmbH & Co KG D-7742 St. Georgen

D&-3G01 G,."&Lgr;, April 22, 1991 011-MH

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Fig. 3 A shows a contour 31 in the form of a general conchoid, as it extends around a center Z, 30.-

This curve thus represents the development of a constant 33 with a superimposed sine function 32, as shown in Fig. 3 B in Cartesian coordinates.

In a simpler embodiment, it is sufficient to provide an approximately oval or elliptical edge 8 of the rotor part. In another embodiment, the rotor part has approximately the shape of a number 8 or the shape of a so-called lemniscate.

In Fig. 3 A, the edge of the rotor part 7 is designed in such a way that there are exactly two maximum expansions in the radial direction over a 360 degree mechanical angle.

Of course, the rotor part can have a different number of radial maximum extensions, in particular only one per 360 deg. mech., which results in an eccentric or conchoid-shaped contour, or also 3, 4, 5, 6, etc. per 3 60 deg. mech., so that contours in the shape of a cloverleaf etc. are obtained.

Oval or circular shapes are also advantageously provided for the contour 48 of the sensor coils. (Fig. 4 A )

In another embodiment, the coils have the shape of circular sectors or sectors of circular rings, i.e. the radial boundary lines of the coils are approximately straight and enclose an angle alpha, reference numeral 41. (Fig. 4 B, Fig. 4 C)

PAPST-MOTOREN GmbH & Co KG "'''^; DE-3001 G "'^ D-7742 St. Georgen 22 April 1991

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The coils typically have initial contacts and end contacts 46 and are limited by an inner diameter 42 and an outer diameter 42.

A correction contour 44 is also provided for the fine definition of an inductance curve L(phi) over the angle of rotation of a rotor part 7.

In a further embodiment, the coil shape is derived in such a way that the development of the coil results in a surface that is bordered by a function similar to a cosine function. (Fig. 4D).

The harmonic analysis of the boundary of such coils therefore results in a set of periodic functions, of which one function is comparatively strongly represented and corresponds to the dominant boundary function of the rotor part.

Fig. 5 shows the basic arrangement of a single coil 51 or a set of coils in interaction with an oscillator circuit 50. There are many circuits for this purpose that are known to those skilled in the art.

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D-7742 St. Georgen 22 April 1991

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Normally, 50 oscillators are used for each

frequency-determining capacity 55 is required. This capacity is

usually for all oscillators of the same size.

According to known gyrator circuits, it is of course also possible to use another coil instead of the capacitance 55, so that deviations of the capacitance values from a nominal value no longer play a role.

As indicated in Fig. 5, the inductance 51 is influenced by the presence of either ferromagnetic materials 52 or diamagnetic materials 53, or by a combination of both such materials.

Depending on the coverage of a coil by a rotor part with the above-mentioned properties, a variable frequency of the oscillator 50 results. This can be tapped at the output 56 opposite the ground potential 57 and further processed.

Fig. 6 shows how, due to the threefold nature of the coils per sensor and a preferred twofold nature of the rotor part 7, a different course of the inductances occurs over the rotational position (phi or χ) of the rotor part. The curves are similar to one another, but have characteristic phase offset dimensions delta gamma 1, delta gamma 2 and delta gamma 3 with respect to a characteristic passage through a mean value line. With a threefold coil arrangement, these angles are in principle exactly 120 deg. el.

PAPST-MOTOREN GmbH & Co KG ^ = ",, qE-3 00*1 G '■■■'^;'^; D-7742 St. Georgen 22 April 1991

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As can be seen, each angle phi or each position x of the rotor part 7 corresponds to a unique combination of three inductance values or three oscillator frequency values.

Since the functions shown have a sinusoidal character, this means that the position of the rotor part 7 can be clearly determined by back-calculating from three measured inductance values. Comparable relationships for determining the position of a rotor from several inductance values are presented in more detail in the PCT patent publication WO 90-15473.

Fig. 7 shows a related representation of such an algorithm for the analysis of three frequency signals for the purpose of determining the rotor position of a rotor part 7. Fig. 7 has an abscissa 70 in the x-direction and an ordinate 71, which serves as a scale for measured frequency values of the oscillators. Both axes cross at the origin. First, the values of measured frequencies fl, f2 and f3 are entered at equal (equidistant) intervals, as symbolized by points 72, 73 and 74. This representation is in principle continued periodically by (also equidistant) values fl ¹ , etc., of which, however, only fl' is shown with reference number 72', since the relationships shown in principle do not provide any further information.

For the entered values fl, f2, f3, a sine function is constructed which has a period that corresponds to the x-distance between 72 and 72' and which passes exactly through all three points 72, 73 and 74. Such a

PAPST-MOTOREN GmbH & Co KG ,."'? ": - &idigr;?&Egr;^·3&phgr;&idiagr;'&udiagr;"&iacgr;&Igr; D-7742 St. Georgen 22 April 1991

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The sine function fluctuates around a base line 76, which intersects the sine function at two points, 75 and 75'. From point 75, the perpendicular is dropped to the abscissa 70 and results in the base point 78, whose distance from the origin 77 is designated as Theta. This value Theta now varies with rotation of the rotor part 7 in a directly proportional manner, whereby the period length between 72 and 72' directly corresponds to a periodicity of the sensor of 360 deg. el. This relationship is more precise the more precisely the inductance functions Li from Fig. 6 can be represented by a sum of constant value and pure sine function.

It is therefore an object of the present invention to take all appropriate measures to realize such a harmonious course of the functions of measured values. Depending on the structure of the electronic circuit, it is desirable either to provide the inductance function directly with a modulation in the form of a sine function (in the case of gyrator circuits) or to give the function /V L (phi)\ a form with particularly few harmonics (in the case of L/C oscillator circuits).

For many applications, however, the alternative consideration between the inductance curve and the oscillator frequency curve is of less importance, since the inductance values typically only fluctuate by about 5 ... 10 %.

Accordingly, the relationship between inductance change and frequency change is proportional to a first approximation, according to the relationship

V( 100 % + 2*a % ) * (lOO % Ta % ) ~~ * for values of a in the range from about -10 to +10 .

PAPST-MOTOREN GmbH & Co KG "'*' '· DE»-3QC>1 G-" -D-7742 St. Georgen April 22, 1991

O H-MH

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If the resolution requirements of the sensor are less stringent, approximate constructions are sufficient to determine the angle Theta as shown in Fig. 7.

An important approximate solution of this kind is based on the fact that in the case of a three-fold coil set, an approximate value of 3/2 = 1.5000 is used instead of the exact value for V3 = 1.73 2... This allows the numerical calculation of the value for theta to be significantly accelerated using a microprocessor or microcontroller.

It is clear that the procedure described is not limited to the analysis of three measured values, but

can also be carried out with/4, 5, 6, 7 etc. measurements. &Lgr;

In this case, a sine function must be sought that connects the measured values with the best approximation. This is preferably calculated using a discrete Fourier transformation or with directly equivalent measures such as a center of gravity analysis. In addition, other analysis methods are available, such as correlation analyses, analyses using so-called artificial neural networks, so-called fuzzy logic, etc. These essentially provide comparable analysis results. However, they are currently characterized by a higher hardware outlay.

It is clear that in this approach the period of the sine function should correspond to the period of all measured values.

If the measured values do not fall on such a sine function (where additional constant terms are initially disregarded here

PAPST-MOTORS GmbH & Co KG D-7742 St. Georgen

&Idigr;3&Egr;-3&Oacgr;&Ogr;1 ⁴ Q *-' 22 April 1991 O H-MH

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remain), this is equivalent to the existence of higher harmonics (i.e. sinusoidal harmonics). A clear reconstruction of the desired rotor position is then not possible without corrective measures (e.g. using tables).

It is clear that the variation of the coil inductances Li according to Fig. 6 or the variation of the associated oscillator frequencies according to Fig. 2 should have as few harmonics as possible, i.e. that it should be a pure sine function.

The higher harmonics of the function are then comparatively weak compared to the fundamental wave (first harmonic).

Fig. 8 shows a further measure according to the invention, according to which it is possible to combine the ferromagnetic portion of the rotor part 7, which can also be made in the form of sintered material, with a portion of diamagnetically acting material. Contour 81, for example, borders the ferromagnetically acting component of the rotor 7, while contour 82 borders the diamagnetically acting component.

To avoid eddy currents in the rotor, the individual parts of the rotor preferably have slots 83, 84

on.

Preferred embodiments of the sensor are shown in Figures 9 to 12.

PAPST-MOTOREN GmbH & Co KG ,_%-"'''-',P^"? ⁰⁰¹ IF ,L D-7742 St. Georgen 22 April 1991

O H-MH

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Fig. 9 shows a two-bladed rotor part which is rotated around the point of penetration of an axis 3 0 .

Its edge 90 runs exactly according to a general conchoid and has minimum radii 92 at two points on the circumference and, offset by 90 deg. mech., maximum radii

Another border of this type is shown in Fig. 10, which also has an exact border in the form of a conchoid. However, the parameters of the border curve are selected so that in the area of the minimum radii 102 there are almost straight side pieces. In the area of the maximum radii 101, on the other hand, there are almost circular arc-shaped contours.

Another edge of this type is shown by another conchoid 110 in Fig. 11. This is also rotated around the point of intersection of an axis 3 0 and, due to the selected parameters, has only a minimum radius 112 and a maximum radius 111. A rotor with this edge is particularly suitable, for example in conjunction with a stator part with three inductances, for emitting a clear position signal over 360 deg. mech., i.e. 360 deg. el. of the position signal corresponds to 360 deg. mech.

A preferred coil design for inductances of the stator part of a sensor is shown in Fig. 12. Here, the three inductances 123, 124 and 125 each extend over an angle alpha (reference number 122) of 90 deg. mech. and are arranged symmetrically over the full circle. They are surrounded by the outer diameter 13 0

PAPST-MOTOREN GmbH & Co KG <VV DP-3001 G,- _r i, D-7742 St. Georgen 22. April 1991

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and inwardly by the inner diameter 121, relative to a sensor center 120, which is coaxial with a rotor axis 30.

The connection points 126 and 127 of a coil are connected to an electronics, e.g. in the form of an integrated circuit 128, which in a preferred embodiment has a frequency-determining capacitor 129.

It is understood that the application possibilities of the rotary position sensor according to the invention are diverse and in addition to using the sensor as a rotary position indicator for any motor, smaller and miniaturized versions can also be produced, such as those required in computer peripheral devices or for monitoring valves or throttle valves.

Claims (1)

PAPST-MOTOREN GmbH & Co KG 20 June 1991 D-7742 St. Georgen DE-3001 G 011-MH Expectations: Sensor, in particular for rotary movements, with variable inductances in the form of flat coils, which are in particular designed in the form of printed circuits and change their inductance characteristics depending on the presence of one or more metallic or ferromagnetic or diamagnetic objects, the inductances and at least one of the said objects being movable relative to one another, characterized by the following features: - there are at least two separate inductors, - there is a device for determining the characteristics of the inductances, - there is a device for carrying out a pattern analysis which analyses the characteristics of the inductances, in particular by means of a harmonic analysis, - there is a device which converts the result of the pattern analysis into a position value. Sensor according to claim 1, characterized in that the objects consist at least partially of a metallic sheet or sintered material, preferably iron sheet or aluminum sheet. PAPST-MOTOREN GmbH & Co KG 20 June 1991 D-7742 St. Georgen DE-3001 G 011-MH Sensor according to claim 2, characterized in that the objects have a defined edge or a defined effective edge. Sensor according to claim 3, characterized in that the edge of the objects has at least approximately the shape of a general conchoid. Sensor according to claim 3, characterized in that the edge is approximately oval-elliptical in shape or approximately has the shape of a number "8" or at least approximately has the shape of a lemniscate. Sensor according to claim 3, characterized in that the boundary or effectively acting boundary of the movable part of the sensor represents the development of a function which is defined by a constant term with additively superimposed sinusoidal oscillation. Sensor according to one of the preceding claims, characterized in that the inductances have a substantially straight edge on at least one side in a preferably radial direction. PAPST-MOTOREN GmbH & Co KG 20 June 1991 D-7742 St. Georgen DE-3001 G 011-MH Sensor according to one of the preceding claims, characterized in that the inductances have a curved edge on the sides. Sensor according to one of the preceding claims, characterized in that the inductances are preferably arranged in a stationary manner and the metallic objects are arranged so as to be rotatable about an axis, which axis is directed essentially parallel to the normals of the inductances or coils Sensor according to one of the preceding claims, characterized in that the inductances represent a frequency-determining element of oscillators, the oscillation frequency of which is changed depending on the presence and degree of coverage by a preferably metallic or ferromagnetic object, wherein with uniformly progressing movement of the object a frequency variation of the oscillators of at least approximately sinusoidal course is carried out and the inductances are arranged such that the approximately sinusoidal course of the frequency variations has a defined phase offset among each other, which phase offset is at least approximately an integer fraction of 360 deg. el., in particular e.g. 120 deg. el. PAPST-MOTOREN GmbH & Co KG 20 June 1991 D-7742 St. Georgen DE-3001 G 011-MH Sensor according to one of the preceding claims, characterized in that an arrangement for carrying out a pattern analysis is present, which consists of an electronic circuit, in particular a microprocessor circuit or a microcontroller. Sensor according to one of the preceding claims, characterized in that the metallic objects have at least a portion in the form of a piece of sheet metal made of amorphous metal. Sensor according to one of the preceding claims, characterized in that the metallic objects rotatable about an axis have slots for reducing eddy currents, which slots preferably extend in a radial direction with respect to said axis. Sensor according to one of the preceding claims, characterized in that the variation of the oscillator frequencies with progressive movement of a movable part of the sensor has a periodic function curve, the higher harmonics of the function being comparatively weakly pronounced in comparison to the first harmonic. PAPST-MOTOREN GmbH & Co KG 20 June 1991 D-7742 St. Georgen DE-3001 G 011-MH Sensor according to claim 14, characterized in that the third and higher harmonics of the function are practically completely suppressed. Sensor according to one of the preceding claims, characterized in that the objects (rotor parts) have a ferromagnetic component or a component with diamagnetic properties, individually or in combination. Data processing system with a connected peripheral device in the form of a so-called "mouse" or a so-called "trackball", which peripheral device has sensors for converting rotary movements into electrical signals, characterized in that that the sensors have at least two separate variable inductances in the form of flat coils, which are designed in particular in the form of printed circuits and whose inductance characteristics vary depending on the presence of one or more metallic or ferromagnetic or diamagnetic objects, the inductances and at least one of the said objects being movable relative to one another and PAPST-MOTOREN GmbH & Co KG 20 June 1991 D-7742 St-Georgen DE-3001 G 011-MH the edge of the objects being at least approximately oval-elliptical in shape, or in the form of a general conchoid, or approximately in the form of a number "8" or at least approximately in the form of a lemniscate. Drive system with a motor, in particular electrically, pneumatically or thermally operated, and with a sensor device for detecting the rotary movement or angular position of the motor axis, characterized by the following features: - the sensor device has as a converter at least two separate variable inductances in the form of flat coils which are designed in particular in the form of printed circuits and whose inductance characteristics vary depending on the presence of one or more metallic or ferromagnetic or diamagnetic objects, the inductances and at least one of the said objects being movable relative to one another, - there is a device for determining the characteristics of the inductances, - there is a device for carrying out a pattern analysis which analyses the characteristics of the inductances, in particular by means of a harmonic analysis, - there is a facility which converts the result of the pattern analysis into a position value. ^