DE102007022627A1 - Absolute angle inductive and contact-less measuring device, has electronic circuit measuring inductance of coils, energy of electromagnetic fields, performance of resonance circuit or phase angles between current and voltage of coils - Google Patents

Abstract

The device has a shaft (4) with a bevel (14), where the shaft is arranged within an interior (3) of two circular coils (2.1, 2.2), and is rotatable around its axis (5). Middle point of the coils is provided at a distance from the axis. The connecting lines of the middle points form a rectangular angle with the axis. An electronic circuit is attached at each coil over a connection (6), for measuring inductance of the coils, energy of electromagnetic fields of the coils, performance of resonance circuit or phase angles between current and voltage of the coils.

Description

The The present invention relates to a device for inductive, contactless Measuring the rotational position over 360 ° with a shaft of steel or other materials, with a flattening to the D-wave as a donor, the existing in a device or a machine Wave can be used as a donor. It is applicable as a replacement of potentiometers, encoders, wheel sensors, steering angle sensors in a fullness of applications, everywhere where the angle of rotation of an axle or shaft is of interest and to Taxes or rules should be measured and has a mechanical conceivably simple construction. In a further embodiment of the shaft, Comparable to a snail, the flattening becomes a feed rotated and so the angle of rotation changed over the feed of the shaft, so that determines the linear position without contact can be.

In become known devices for measuring the absolute rotational position at potentiometers, tracks with known electrical resistance mechanically tapped and the voltage ratio of the railway resistors as Measured used.

Of the obvious disadvantage of this solution is that this mechanical tap is subject to wear and so changes of the measured value up to the failure of the potentiometer over the Lifespan can arise. This is not practical in many applications. In addition, the measuring range usually only 270 °.

Other Solutions, like optical encoders or magnetic rotary sensors work largely wear. An obvious disadvantage of optical encoders is that that the mechanical effort for Storage of the shaft, flanges and evaluation quite high and thus is expensive. Magnetic systems attempt to avoid this however, magnets on the shaft to be measured, which are sensitive to high temperatures and mechanical loads are and beyond collect ferromagnetic dust in their environment. This too leads to Incorrect measurements via the lifetime.

task It is therefore advantageous for the present invention to have a sensor arrangement form, with which determines the rotational position of a shaft inductively and the accuracy of the measurement reaches at least 1%.

A circular Arrangement of conductors on a flat substrate, is called planar Coil considered a certain inductance and by means of a electronic circuit with a current of known size It generates an electromagnetic field. Inside the coil will eccentrically mounted a bore in the substrate, so that the hole at a point of the innermost turn as possible comes close. This place is the zero point. Then in this hole a shaft made of an electrically conductive material with a flattening introduced to the D-wave. This shaft is rotatably mounted elsewhere about its central axis and perpendicular to the plane of the coil. The angle of rotation is now the angle between the edge of the flattening and the tangent to the coil at the zero point.

Of the Current through the coil generates an electromagnetic field with a certain energy. In case of change of the current eddy currents are induced in electrically conductive materials and the measurement of the energy is reduced by the amount of energy of the eddy currents and measurable. Here is the size of this eddy currents quadratically proportional from the distance between the conductor and the conductive surface, the surface the D-wave.

If the angle of rotation is 0, the flattening is at point P of the coil at next and the distance of all surface elements the D-wave to the conductor tracks of the coil largest. Now the D-wave rotated, so the flattening away from the coil, conductive material will be closer brought to the tracks, causing proportional bigger losses through the eddy currents.

Of the Energy loss through the eddy currents can be associated with all known Method for measuring an inductance, as a change in the inductance, resonant frequency or change the goodness a resonant circuit or phase angle between current and voltage be determined.

Becomes now a second, identical planar coil also at 90 ° to the first rotated, as eccentrically mounted on this support, so can be measured be whether the rotation from the zero point to the left or right he follows. Thus, the rotational position according to the invention over a whole revolution clearly certainly. Practical measurements show a resolution of the angle to about 0.1 °.

moreover It is advantageous that the shaft is displaced in the direction of its axis can be, without affecting the measurement, and that the flattening can be mounted on the shaft at a certain pitch, so that the translatory feed of the shaft like a rotation becomes determinable.

This object is achieved with the characterizing parts by the patent claim (1). Advantageous embodiments of the invention Device result from the measures in the dependent claims.

The inventive arrangement two planar coils and a D-wave has compared to previously known solutions the advantage that so that the mechanical complexity is minimal and only the electronic evaluation is added.

Farther it is advantageous that in the arrangements with four planar coils their geometric arrangements used to improve the accuracy can be, two coils are opposite each other and the measurement becomes so differential, or the arrangement for measuring the linear Position is used.

Further Advantages and details of the device according to the invention arise from the following description of several embodiments with reference to enclosed figures.

there shows

1 as a 3D sketch of a carrier, each with a circular, planar coil on top and bottom, eccentrically arranged to the bore with a rotatable D-wave with flattening, the coordinate system X, Y, Z with rotation angle φ and two electrical connections to the transmitter;

2 two planar circular coils in plan view, rotated eccentrically by 90 °, their centers, the rotatable D-shaft in section and their electrical connections;

3 four planar circular coils in plan view, each eccentrically rotated by 90 °, their centers, the rotatable D-shaft in section and their electrical connections;

4 a section through the support with 2 layers and a planar coil per surface and the shaft in bore;

5 a further exemplary arrangement of planar coils in the plan view, wherein the carrier is divided and the parts of the coils are electrically conductively and detachably connected via connectors, and the parts can be fastened together by means of mechanical elements;

6 a further 3D view of the carrier with the eccentric, planar coils, the coordinate system, the angle φ and the Z-direction linearly movable shaft in skeletal representation, on which the flattened is mounted rotated with a slope;

7 a shaft with the flattening in cross section;

8th a shaft without flattening with a coating or film that does not completely cover the circumference;

In 1 is a first embodiment of the inventive arrangement, each with an identical, planar, circular coil ( 2 ) on the top and bottom of the carrier ( 1 ). The spools ( 2 ) have several turns and are eccentric to the bore ( 3 ) turned by 90 degrees. The bore ( 3 ) in the carrier ( 1 ) is positioned so that the point (P) is the shortest distance between the innermost conductor of the coil ( 2.1 ) on the top and the bore edge; in the hole ( 3 ) is the wave ( 4 ) and is rotatable about the coordinate axis Z. The angle of rotation φ to be measured is described by the tangent (8) to the innermost conductor track of the coil (FIG. 2.1 ) at point P and the extension dr edge ( 9 ) of the flattening of the shaft ( 4 ). About the connections ( 6 ), the coils are connected to the evaluating electronics.

2 shows two coils ( 2.1 . 2.2 ) in plan view one above the other on the top or bottom of the carrier. The inner diameter (e) of the coils ( 2 ) is greater than the diameter d of the shaft ( 4 ), which is also slightly smaller than the diameter of the hole ( 3 ), so that the shaft ( 4 ) with the distance r to the innermost conductor of the coil ( 2.1 ) can rotate freely. The distances b1, b2 of the centers ( 7.1 . 7.2 ) of the coils to the axis ( 5 ) the wave ( 4 ) are equal and the flattening h of the wave ( 4 ) of its diameter increases the distance of the electrically conductive surface of the shaft ( 4 ) from the conductors of the coils ( 2 ). The angle φ between edge ( 9 ) of the flattening and tangent ( 8th ) at point P is zero, if the flattening ( 14 ) is closest to the point P.

Is the current in the coils ( 2 ), in the faces of the D-wave ( 4 ) Induces eddy currents and the energy in the electromagnetic field of the coils ( 2 ) is reduced by this power loss. This power loss of the eddy currents depends on the distance of the contour of the D-wave ( 4 ) to the tracks of the coil ( 2 ). Is the flattening ( 14 ) near the point P and parallel to the tangent ( 9 ), all points on the contour of the wave ( 4 ) the largest distance from the tracks of the coils ( 2 ) and the power loss is the lowest. When turning from this position (φ = 0), contour elements of the arc of the shaft ( 4 ) the flattening ( 14 ) and the contour moves ever closer to the tracks. As a result, the power loss through eddy currents increases and this can be determined with a measuring electronics.

3 describes in addition the example Arrangement of four coils ( 2.1 . 2.2 . 2.3 . 2.4 ) one above the other on a multilayer carrier ( 1 ), so that two coils are opposite each other. Important here is only the arrangement of the coils in the coordinates X, Y and that they are electrically isolated from each other, but not the distance in Z. About the connections 6 the electrical connection is made with the measuring electronics, which can measure the coils each sequentially but also all at the same time or in any combination.

4 shows an exemplary section through the multilayer carrier ( 1 ) and the wave ( 4 ) in the opening ( 3 ). Layers ( 1.1 . 1.2 ) of the carrier and the layer ( 10 ) act as insulators between the coils ( 2 ). As long as the mechanical stability and geometric accuracy of the coils are ensured, all manufacturing methods and arrangements of the coils ( 2 ) are considered equivalent. Planar coils on electronic boards only have the advantage of good reproducibility in the manufacturing process.

5 shows a further exemplary embodiment of the sensor arrangement according to the invention, largely analogous to 2 and 3 , Different is the separation of the carrier ( 1 ) in two parts ( 1.11 . 1.12 ) with the dividing line in the direction Y through the axis ( 5 ) the wave. This allows the arrangement also on waves ( 4 ) can be adapted if no end of the shaft is freely accessible and in the opening ( 3 ) can be introduced. This requires that all 2 or 4 coils are split and two detachable connectors ( 11 ), so that the halved coils ( 2 ) can be electrically connected to each other again when they are the shaft ( 4 ) enclose. With the fastening elements ( 12 ) one half ( 1.12 ) stable and detachable on the other ( 1.11 ) attached. The fastening elements ( 12 ) also part of the connector ( 11 ) be.

6 shows a further embodiment of the sensor arrangement according to the invention for determining the linear position of the shaft (FIG. 13 ), which is not rotatable but slidably mounted in the direction Z and on the flattening 14 twisted with a slope was attached. This is done in the plane of the coils ( 2 ) a rotation angle φ, which depends on the absolute linear position and thus enables their measurement. This measurement is unique and can be scaled using the slope.

7 shows the D-wave ( 13 ) in cross section with the flattening ( 14 ) in the measuring range of interest and the full circular contour outside. The wave ( 4 . 13 ) preferably consists of an electrically conductive material, but it can also be used with ferromagnetic properties.

8th shows a further embodiment of the shaft ( 4 . 13 ) of an electrically non-conductive or sufficiently low conductive material, such as plastic without flattening. The conductivity is determined by partial coating ( 15 ) with a conductive substance or such a film. The flattening ( 14 ) now corresponds to the uncovered area of the shaft. This structure can be both the straight D-wave ( 4 ), as well as the twisted shaft ( 13 ) and in turn only be part of a larger element.

A coil with the inductance L is traversed by a current I. Describing the relationship between these quantities and the energy of the electromagnetic field generated around the coil e L = 1/2 · L · I 2 (1)

If this energy e _{L is} reduced by an induced eddy current I _E , the relationship arises: e L = 1/2 · L · (I - I e ) 2 (2)

This energy can be determined with different measuring methods and the size of the eddy currents can be experienced as an apparent change of the inductance, the quality in the resonance circuit, the phase angle between voltage and I or a measuring voltage U. For the sake of clarity, the measuring voltage U proportional to e will be used hereinafter. U L ~ e L (3)

This voltage is used for the coils ( 2.1 . 2.2 ) acc. 2 over a rotation of the shaft ( 4 ) and empirically determined according to the eddy currents: U L1 = O + a * cos (φ) (4) U L2 = O + a · sin (φ) (5)

In this case, O describes the offset or the fundamental voltage of the measurement and a the amplitude of the oscillation over a full revolution. Substituting (4) into (5) yields U L1 - U L2 = a · cos (φ) - a · sin (φ) (6) independent of the offset. By reshaping, the angle φ can now be determined: φ 0 = ½ arcsin (1 - (U L1 - U L2 ) 2 / a 2 ) (7) if the flattening is close to P and the demand U L1 > O (8) is satisfied. Otherwise applies φ = φ 0 + 180 ° (9)

Now the amplitude a is unknown. Checking the maximum values for U _L1 and U _L2 according to the sine function yields
U _L1 = max .: φ = 0 °; a = U _L1 - U _L2
U _L2 = max .: φ = 90 °; a = U _L2 - U _L1
U _L1 = min .: φ = 180 °; a = U _L2 - U _L1
U _L2 = min .: φ = 270 °; a = U _L1 - U _L2
and can be saved for further evaluation. This shows the inductive determination of the angle of rotation.

Further embodiments of the sensor according to the invention emerge from the consideration that it is often desirable to always determine the amplitude a directly. This succeeds with the sensor arrangement accordingly 3 where 2 more coils are rotated 180 ° to the first two introduced: U L3 = O - a · cos (φ) (10) U L4 = O - a - sin (φ) (11)

By substituting into equations (4) and (5), by simple transformation, one obtains: φ = arctan ((U L2 - U L4 ) / (U L1 - U L3 )) (12) with complete, direct calculation of the angle.

A further design possibility of the sensor arrangement according to the invention results when the carrier ( 1 ) Shares through the center of the bore into two parts and the interconnects of the four coils via connectors releasably connects together again. The advantage is in the assembly, because the sensor assembly can be mounted on an already mounted shaft, without having to remove the while.

The measurement of the linear position is realized with the sensor arrangement according to the invention, in which the shaft (FIG. 4 ) not rotatable, but along its axis ( 5 ) is displaceable relative to the sensor arrangement and the flattening ( 14 ) is mounted twisted with a slope dφ / s. Thus, the feed produces an apparent rotation of the shaft ( 4 ) which can be clearly assigned to the translational position within 360 ° over the slope. With the slope, this rotation can be mapped to paths of different lengths. In addition, in the case of several revolutions of the flattening ( 14 ) on the shaft ( 13 ) from the absolute displacement sensor an incremental encoder for linear displacement.

In favor of a more cost-effective production, in a further embodiment of the waves ( 4 ) or ( 13 ) are dispensed with the flattening and instead an electrically conductive coating or film is applied to a non-conductive round rod so that the area of the flattening ( 14 ) is not covered. The functionality remains completely intact.

Become instead of electrically conductive materials ferromagnetic substances used with low remanence, although the same functions are measurable, they are however on the changes in the magnetic flux in attributed to the fields of the coils. The Measurement of φ takes place identical.

use can find the sensor arrangement according to the invention Practical in all applications where potentiometers for turning or moving the tap and rotary encoder are used and over the Lifetime mechanical wear should be avoided. Because the mechanical effort for the adaptation is conceivably low, the sensor can also be produced very inexpensively become.

Further interesting properties are that at a diameter of Wave of 6 mm can be achieved very good results. But the diameter the coils and wakes are scalable in a wide range and also allow mechatronic miniaturization for new applications.

Claims (10)

Device for inductive, non-contact measurement of the absolute angle of rotation φ of a shaft ( 4 ), characterized in that A is a wave ( 4 ) of an electrically conductive material with a flattening ( 14 ) and this in the interior ( 3 ) of at least two circular coils ( 2.1 . 2.2 ) about its axis ( 5 ) is rotatably arranged and B the centers ( 7.1 . 7.2 ) of the coils to the axis ( 5 ) have a distance (b1, b2) and C the connecting lines of the centers ( 7.1 . 7.2 ) of the coils with the axis ( 5 ) form a right angle to each other and D via the terminals ( 6 ) an electronic circuit for measuring the inductance of the coils ( 2.1 . 2.2 ), the energy of the electromagnetic fields of the coils, the quality of one with the coils ( 2.1 . 2.2 ) formed resonant circuit or the phase angle between the current and voltage of the coil is electrically connected to each coil. Apparatus according to claim 1, characterized in that A the two coils ( 2.1 . 2.2 ) each on a surface of the carrier ( 1 ) and B of this carrier ( 1 ) a hole ( 3 ) for receiving the shaft ( 4 ) contains. Apparatus according to claim 1 or 2, characterized in that A at least two further coils ( 2.3 . 2.4 ) with the same area as the coils ( 2.1 . 2.2 ) on the support and B the connecting lines of their centers ( 7.3 . 7.4 ) with the axis ( 5 ) form a right angle to each other and C is the midpoint ( 7.1 ) of the first coil with the axis ( 5 ) and the center ( 7.3 ) of the third coil are on a straight line and D is the midpoint ( 7.2 ) of the second coil with the axis ( 5 ) and the center ( 7.4 ) of the fourth coil are on a straight line and E are all centers ( 7.1 . 7.2 . 7.3 . 7.4 ) of the coils to the axis ( 5 ) have the same distance b. Device according to at least one of the preceding claims, characterized in that the carrier ( 1 ) by a cut in the direction Y through the axis ( 5 ) the wave ( 4 ) in two parts ( 1.11 . 1.12 ) and the electrical conductors of the coils ( 2 ) by connectors ( 11.1 . 11.2 . 11.3 . 11.4 ) are electrically conductively and detachably connected to each other. Device according to at least one of the preceding claims, characterized in that the flattening ( 14 ) the wave ( 4 ) only in the vicinity of the coils ( 2 ) is pronounced. Device according to at least one of the preceding claims, characterized in that the shaft ( 4 . 13 ) in the direction of its axis ( 5 ) is movable. Device according to at least one of the preceding claims, characterized in that the flattening ( 14 ) with a feed s around the shaft ( 13 ) is rotated and so the movement of the shaft ( 13 ) in the direction of its axis ( 5 ) a rotation of the flattening with respect to the coils ( 2 ) causes. Device according to at least one of the preceding claims, characterized in that the coils ( 2 ) against the wave ( 4 . 13 ) are rotatable or displaceable. Device according to at least one of the preceding claims, characterized in that the shaft ( 4 . 13 ) consists of a ferromagnetic material. Device according to one of claims 1 to 9, characterized in that A the awkward ( 4 . 13 ) made of an electrically non-conductive material ( 16 ) and the electrical conductivity by coating with an electrically conductive material ( 15 ) or applying an electrically conductive layer ( 15 ) and B is the flattening ( 14 ) can be omitted if the corresponding surface is not made electrically conductive.