GB2533191A - An eddy current sensor and a method of using an eddy current sensor - Google Patents

Abstract

A method of using an eddy current sensor to provide an indication of a displacement-dependent parameter of a target object 2, by interaction between the target object 2 and a planar sensor coil 3. The target object 2 is moved through an opening in the sensor coil 3, whereby the field strength in the area of the flat coil 3 changes as the target object 2 moves. Magnetic field changes are detected by an evaluation circuit (14, figure 4) and transmitted to a microcontroller (13, figure 4) which processes the signals of the evaluation circuit (14, figure 4) and provides the latter with said signals via an output and protection circuit The target object 2 is moved axially through the coil. The target object may have a varying geometry with a continuously changing cross section, for example a conical shape. The eddy current sensor may be disposed in a sleeve or tubular secition and may be provided with a printed circuit board. A resilient structure (for example a spring: 7, figure 3) may be applied to the target object 2.

Description

An eddy current sensor and a method of using an eddy current sensor The present invention relates to an eddy current sensor and a method of using an eddy current sensor to provide an indication of a displacement-dependent parameter of a target object, by interaction between the object and the sensor. Such a method includes a path measurement method using a sensor which cooperates and/or interacts with a target object and which is based on the so-called eddy current principle. The invention further relates to the detection of paths of target objects which are disposed in the vicinity of a sensor coil. The sensor and the associated target object are moveable relative to one another. The invention further relates to a sensor for path measurement.

Various embodiments of inductively operating sensors for path measurement are known from practice. In particular, contactless path measuring systems are known which provide information on the motions of associated target objects or specific transducer elements based on changes in magnetic field strength.

In known assemblies, for example, cylindrical coils are used into or out of which the target objects are moved. The target objects have at least geometrically irregular shapes influencing the magnetic field when passing through the coils.

Furthermore, inductive position sensors for use as so-called limit switches are known in which the target object is moved towards the inductive sensor and stopped in front of or by means of the latter, with the changes in field strength being detected and processed into a measurement signal.

It is known to combine the inductive position sensors with electronic units in order to be able to generate a standardized measurement signal which can be processed in subsequent control devices.

A further known method of path measurement is based on the mode of operation of the ideal plate capacitor. The two plate electrodes are provided by the sensor and the opposite target object. In the event that a constant alternating current flows through the sensor capacitor, the amplitude of the alternating current on the sensor is proportional to the distance between the capacitor electrodes. Capacitive sensors are designed for contactless path, distance and position measurements. The change in distance of the target object from the sensor is detected by means of a controller, processed and provided as a measured value for further process stages. In order to achieve a reliable measurement, an unvarying dielectric constant between the sensor and the target object must be ensured, because the measuring system does not only depend on the distance from the electrodes but also reacts to changes of the dielectric in the measuring gap. Therefore, capacitive position sensor systems are especially used for high-precision applications in laboratories and industry, for example in clean-room areas. For this reason, however, they are dependent on a clean and dry environment. Furthermore, they are complex both in terms of production and application.

Sensors are especially required for transmission devices which, for functional reasons, have to perform a linear motion.

This also includes mechanical parts moving back and forth as well as transmission devices in motor vehicles and engines. The location of specific elements must commonly be determined to know the latter's position and be able to start the next steps via downstream control systems.

Such functions are especially performed in manual transmissions, hydraulic valves and cylinders, clutches and various actuating elements, such as foot-operated pedals.

Furthermore, the detection of shift positions of shift rods in automated transmissions, the detection of thermal expansions of a material or a product, measurements of radial roll shiftings, applications in combustion engines, brake pedals and much else are, inter alia, fields of application for the sensors.

Whilst using the sensors in the above cases, they are heavily exposed to moisture, dirt, oils, greases and mechanical stresses. Therefore, it is desirable to provide sensors for high precision in a rough industrial environment including stress, dirt and temperature.

For such applications, more and more sensor systems are used which work according to the so-called eddy current principle.

The eddy current refers to a current which is induced in an extended electrical conductor in a time-varying magnetic field or in a moving conductor in a magnetic field which is constant in time, but spatially inhomogeneous. Eddy current testing serves, inter alia, for the non-destructive testing of materials as well as the characterisation of materials and is based on the measurement of the amplitude and the phase of eddy currents.

The eddy current principle is used for measurements on electrically conductive materials which may have both ferromagnetic and non-ferromagnetic properties. High-frequency alternating current flows through a coil usually incorporated in a sensor housing. The electromagnetic coil field induces eddy currents in the conductive target object, thereby changing the resulting alternating-current resistance of the coil. This change in impedance produces an electrical signal which is proportional to the distance between the target object and the sensor coil. Eddy current sensors detect distances towards metal objects in a contactless and wear-free manner. The high-frequency field lines emanating from the sensor coil are not significantly disturbed by non-metallic materials, which is why measurements can be carried out even in case of heavy soiling, stress and oil. Furthermore, this special feature allows for the measurement on metal objects coated with plastics, thereby enabling, for example, the detection of layer thicknesses.

An example of the application of the eddy current principle is given in DE 101 17 724 Al, which describes a device for determining the torque on a rotatable metal shaft. A sensor head of an eddy current sensor is radially directed towards a shaft. The electrical conductivity of the shaft changes according to a torque applied to the shaft. This change causes a change in coupling power of the eddy current sensor, which is detected in an evaluation electronics assembly. In this way, it is possible to reliably detect the torque of the shaft without substantial structural interventions, more especially without making substantial constructional changes to the shaft.

A further example of its application is shown in DE 10 2011 102 829 Al relating to a locking device for inhibiting the engagement of the reverse gear of a motor vehicle transmission.

Eddy current technology is generally used to detect a displacement of a part or a linear or rotary change in the spacing of at least two parts and, as a consequence thereof, the associated derivations, for example, of speed and acceleration.

In practical application, however, the aforementioned eddy current path measurement methods only allow for the detection of distances from the target object in the range from 5 mm to 10 mm. Thus, the possible applications are restricted, because requirements in respect of maximum size are imposed on such sensors depending on the place of installation.

Furthermore, in conventional eddy current path measurement sensors, continuous sensing or measurement of the object to be checked was carried out, with specific points or events in the overall sensing or measuring process, for example specific switching points, being singled out. However, this involves an unnecessary restriction of possible uses of the sensor itself.

It is likewise required to reliably transmit the measured values detected by the sensor to the downstream evaluation and control units. In this respect, too, any risk of external influences falsifying the signals should be attended to.

It is therefore an aim of the present invention to propose an eddy current sensor and a method of using an eddy current sensor, in which there is an interaction between the sensor and a target object, or a path measurement method according to the eddy current principle using a sensor which interacts with a target object.

A further aim of the present invention is to develop a contactless sensor to provide an indication of a displacement-dependent parameter in such a way that it is easy to manufacture. The target object may be a simple mechanical part and the inductive sensor is also capable of operating under difficult external conditions. In addition, positioning tolerances are preferably avoided.

A further aim is to construct the sensor as small as possible and to extend the range of measurement.

Furthermore, it is desirable for the eddy current sensor to be designed for the contactless detection of path, distance, displacement, position but also oscillation and vibration. In the context of explaining the present invention, all these functions are also summarized under the term "path measurement".

In addition, the eddy current sensor should reliably function without a housing as well as when accommodated in a housing.

Furthermore, it should be possible to use standard electronics.

Moreover, it should be possible to provide a sensor and a method in which the result of the sensing or detection of motion of a conductive target object is obtained consistently and/or completely so that comprehensive information may be obtained from this complete signal determination, for example the change of gradient from positive to negative and vice versa permits determination of a direction change of the path of motions.

According to the present invention, one or more of these aims is addressed as regards a method of using an eddy current sensor by the features of the accompanying claim 1. As regards an eddy current sensor, one or more of these aims is addressed by the features of claim 4. Preferred features of such a method are set out in claims 2 and 3, and preferred features of such a sensor are set out in claims 5 to 18.

In the following description, exemplary embodiments and claims, the terms listed below are used, having the following meanings: Eddy current -an electrical current generated during a method in which a target object is monitored or detected. During performance of the method, a coil generates a changing magnetic field which induces an eddy current in the material of the target object. When carrying out the method, the strength of the eddy current is detected by the magnetic field generated by the eddy current, using a sensor which also preferably contains the excitation coil. The parameters measured may be the amplitude and the phase displacement relative to the excitation signal. The eddy current method is performed, more especially, on the basis of a known magnetic field which is generated by the sensor coil cooperating with a metal element. Since the interaction between the magnetic field and the metal target changes, an eddy current is generated in the metal target, which in turn causes energy loss in the circuit generating a magnetic field. As the energy loss can be measured and the energy loss increases with increasing interaction which thus leads to an increase in eddy currents, the microcontroller, which also controls the excitation circuit, transforms the energy loss value into an approximate value. By way of completion, reference is made to the explanations in respect of this principle provided in the introductory part of the present description.

Displacement-dependent parameter -a parameter of the target object which is dependent on the displacement thereof relative to a given position; the parameter includes (but is not restricted to) linear or rotary position, speed, acceleration, oscillation and vibration, and whether the target object is located beyond a given threshold position to effect a switching operation.

Metal target -a metal target object which is made from or contains a metal material, for example steel, nickel, copper, aluminium, thus also a plastic part coated with a metal layer.

Microcontroller -an electronic circuit which may combine functions of an oscillator for the excitation of an oscillating circuit, a voltage regulator, an evaluation circuit as well as an output and protection circuit.

Path measurement method -a measurement method which is suited to detect the change in position of a target object or a transducer element in an axial direction, and to transform it into electrical signals by means of a sensor.

Planar -a feature of the coil and/or its layers meaning for example that it or they are being substantially flat, plane, preferably even, straight, smooth, or non-corrugated.

Position sensor -a device which does not only detect the path and the distance but also the displacement, position as well as oscillation and vibration.

Sensor -a physical unit which is capable of detecting changes in field strength, such as caused by a moving target object, by means of a measuring coil arrangement. The term is understood to mean, more especially, a sensing element, a pickup, a measuring element, a detector, a probe, although this is not intended as a limitation.

Sensor coil -a part which is composed of a plurality of partial windings and/or layers and which generates the magnetic field required for the purposes of measurement, monitoring or detection, preferably in cooperation with an oscillator. Preferably, it is made from copper.

Shaft -comprises in terms of geometry a shaft, handle, flag, drawbar, full-floating axle, drive shaft, axle, spindle or roller, more especially a metal target and/or a measurement object.

Target object -a part, including a measurement object, preferably a part of a mechanical device, which is capable of performing a motion, for example a longitudinal motion, thus influencing the existing magnetic field of the position sensor. Target object is understood to incorporate within its 5 meaning a transducer element, which is an element that provides an indication of one of its physical parameters as an electrical, magnetic or inductive transducer signal.

In accordance with the present invention, there may be provided a path measurement method for a sensor as well as a sensor, in which the sensor coil is configured in such a way that it comprises a number of individual windings which in turn are interconnected to form the sensor coil.

The examples mentioned in the present description do not involve any limitation whatsoever. They merely serve the purpose of providing, inter alia, an example of functions or effects.

Preferably, sensor detection is performed in a completely contactless and/or touchless manner.

Furthermore, it is especially preferred that sensor detection is performed by automatically detecting the application conditions and/or environmental conditions and/or by adapting to these conditions, for example to the current position of a gear selector lever in a motor vehicle.

Furthermore, in accordance with the present invention, there may be provided a position sensor with a sensor coil which is composed of a plurality of planar windings. The planar coil which is likewise formed by the planar windings may, of course, be configured to form a ring or any other desired geometrical structure.

The required magnetic field may be generated through a choice of an appropriate number of the individual planar coil or coils by suitably interconnecting the latter if desired.

In many cases, a coil is provided as a target object.

A plurality of windings are preferably insulated from each other, for example by means of customary insulating materials, such as epoxy glass fabrics, which can be selected by the user in a product-specific manner depending on the intended use.

The individual coil and/or the plurality of coils may be formed by a multilayer printed circuit board (so-called PCB) which in turn comprises at least two planar windings. Here, the known etching method may be applied for production, but other manufacturing methods are also possible.

In an embodiment of the present invention, the thickness of such a multilayer coil may be limited to 1,0 mm to 1,6 mm or may even be less. In another embodiment, the thickness may, however, be greater depending on the area of application or the required expenditure in manufacturing.

Windings arranged on top of each other on various layers are preferably connected in series. The printed circuit board may have, for example, two layers facing upwards and downwards. In addition, further layers can be provided in the manner customary.

The planar windings may be each arranged on a carrier medium.

Thus, by choosing an appropriate number of such coils constructed in a planar manner, the inductance of the sensor coil may be determined over a wide range, whereby, in cooperation with the oscillator disposed in the electronic unit, the possible operating frequency may also be adjusted over a wide range.

An individual planar winding may be implemented in such a way that, as a single element, it has as large an inductance as possible. In this way, it can be achieved that the number of planar windings to be combined with each other can be minimized.

A preferred embodiment may be that a planar winding is arranged on both sides of a double-sided printed circuit board.

A further preferred embodiment of the sensor coil is implemented if the planar windings are integrated within a so-called multilayer printed circuit board and if more than two planar coils are thereby interconnected.

Apart from the possibility of adjusting the inductance of the sensor coil, a sensor coil having a stable structure may be produced by an embodiment of the present invention, which does not require any additional measures for its protection.

The sensor coil may in turn be formed by a plurality of coils constructed in a planar manner, preferably by means of interconnection. It has surprisingly turned out that, by providing the coils constructed in a planar manner, it is possible to omit ferromagnetic coils, eliminate positioning tolerances, preferably use standard electronics, and, more especially, omit application-specific integrated circuits (so-called ASICs).

Each of the planar windings may be designed with an internal void. This enables a target object to be moved back and forth within the centre of the planar coil.

The planar windings may be appropriately produced using printed circuit technology. It is, for example, possible to arrange one of the planar windings concentrically to each other on either side of a double-sided printed circuit board.

As a preferred embodiment of the sensor coil, a plurality of such planar coils is implemented by producing a multilayer printed circuit board. The resulting cascading of the individual coils allows for the achievement of the required inductance of the coil.

Such a construction of the sensor coil has the advantage that the coil itself does not have to be generated by winding operations on an insulating winding body to be produced separately.

A multilayer printed circuit board provides the sensor coil likewise with the geometry and necessary protection, including fixing and insulating means, which have to be affixed subsequently in other coil forms.

The method for the sensor may comprise tuning the sensor element in combination with an oscillator to a resonance frequency or to a specific oscillating frequency and generating thereby the inductance formed by the sensor coil by interconnecting a plurality of individual windings.

It is preferred that the coil has a centrally arranged hole-like recess or an opening. As a result, the coil may receive a shaft. This shaft may form a target object. The shaft may contain, for example, metal, nickel, copper or aluminium.

The shaft preferably has a tubular design.

The sensor in accordance with the invention is preferably used in conjunction with a target object having a varying geometry, more especially one that changes in cross section.

Preferred embodiments of such changes in cross section are annular grooves, bores, one-sided flat portions or varying materials.

In an especially preferred embodiment, the target object has an area with a continuous transition from a small diameter to a larger diameter, thus enabling a quasi-analogue determination of position.

A further embodiment of the method may be that a part can be moved close to the sensor coil at all and its position may be determined due to its geometrical design.

Furthermore, in the presence of geometrical irregularities, abrupt changes can also be detected and evaluated.

Especially a conical design for example involves a substantial advantage, because the arrangement enables sensing, detecting or measuring by means of an axial motion, without the sensing process being affected or even being disturbed by vibrations or unfavourable factors.

As a result the target object is present in the area of the sensor coil but, in contrast to the coil, can change its position by performing an axial motion and, in contrast to the coil, thus changes in effective cross section. For this reason, a conical design is advantageous.

Depending on the area of application, the person skilled in the art may choose different geometrical embodiments.

This advantage is gained all the more if the shaft is mounted in a sleeve or a housing or in a tubular section, for example by means of a three-dimensional support, which contributes to a further reduction of possible vibrations and thus further enhances accuracy of the sensing process. In this way, it is largely protected against environmental influences.

As a result, the so-called electrical noise is likewise decreased.

With the aforementioned conical design, even great distances from the target object can be detected. With this design, it is possible to detect target objects at a distance of 25 mm to 40 mm and more, but, of course, also at a distance of less than 25 mm.

Vice versa, it is thus possible to reduce the frame sizes of the sensors compared to the conventional prior art. This involves cost advantages with respect to production.

More especially in this preferred embodiment, the target object can thus have a varying geometry, but is nonetheless detected completely, preferably by the longitudinal motion of the target object within the coil. As a result of the different spacing owing to the, for example, conical design of the shaft, the sensor coil detects, for example, the position, the displacement and the distance of a part to be detected or other features, such as defects in the surface texture, when the shaft performs the axial motion.

Instead of a motion of the target object in contrast to the statically arranged sensor coil, by way of kinematic reversal, the sensor coil may, of course, also be configured to be movable, with the target object being static.

The motion of the target object through the coil having a hole-like recess or an opening may be transformed into a linear electrical signal according to the eddy current principle, which is further processed by the microprocessor depending on the requirements. As a result, the user is capable of identifying without difficulty the respective position of the target object.

Thus, deviations from standard results can quickly be detected, for example by predetermined or other known parameters.

The sensor may comprise at least one electronic unit cooperating with a sensor coil, and an electronic connector serving to provide the supply voltage and transmitting signals. The aforementioned components may be combined in a common housing. The housing may be shaped in a customary manner.

The target object may be located in the vicinity of the sensor coil and moved in an axial longitudinal direction, thus changing the field strength in the area of the coil and, at the same time, the frequency of an oscillating circuit from a sensor coil and an oscillator. By means of an evaluation circuit, these changes may be detected and converted into measured variables suitable for further processing. The information obtained may be transmitted by the evaluation circuit to a microcontroller. The latter may process the information obtained using, inter alia, a stored programme sequence and may develop therefrom control signals which can be further processed in external devices. An output and protection circuit may be disposed in the electronic unit for trouble-free operation.

In order to ensure a stable operation and meet the required measurement conditions, a voltage regulator may be further assigned to the electronic unit.

In a further embodiment of the method, when the value of a specific parameter is reached, a switching function according to the characteristic of a so-called threshold value switch may be provided, which may be dependent upon the value of a specific parameter being reached in an oscillating circuit in turn dependent upon an oscillator and the sensor coil.

Furthermore, the target object may have a part by which it is in contact with or connected to an object to be monitored and/or detected. In this respect, that part and the target object may be made from the same material.

That part may be guided centrally by means of a guide. The guide, which produces a support in all three dimensions, may, for example, be an inner ring arranged within the sleeve, the housing or another tube section.

An embodiment of the present invention in the form of a sensor described above can be developed further in different ways.

For this purpose, more especially, a compression spring ensuring the continuous contact of the contact part with the object to be monitored or detected may be assigned to the target object.

Instead of a compression spring, any other elastic, more especially resilient, structure may likewise be used, thereby enabling a motion of the target object in relation to the part to be monitored or detected which is largely free of play.

In an advantageous embodiment in which the system is not capable of providing the target object in the right geometry, location or material, by extending the housing, more especially a plastic encapsulation, by a sleeve, a housing or a tubular section, a spring-loaded target object may be accommodated and enclosed as an integrated sliding object within the sensor housing, with the integrated sliding object being guided through an element which can be placed on either side of the sleeve, the housing or the tubular section. In that case, the target object may remain located on the outside of an encapsulated KB portion, giving a closed and, more especially, sealed system for the electronics portion. A compression spring ensures continuous contact with an actuating mechanism of a system which, for example, may be a plunger or a cam.

In cases where an arrangement of an electronic unit on a printed circuit board of the sensor coil is not possible or considered to be insufficient, an additional printed circuit board may carry this electronic unit and be connected to the sensor coil.

Thus, an embodiment of the present invention provides an advantage that it allows for carrying out a method using a sensor with a sensor coil comprising a plurality of individual planar coils, wherein the sensor can be used over a wide range of parameters, whilst being robust and inexpensive to produce.

The method using the sensor may be carried out in such a way that a target object is arranged in the centre of the sensor coil and is capable of moving along the coil axis.

The mode of operation of the method may comprise activating at first an electronic unit arranged in the sensor by applying an operating voltage. An oscillator may be present in the electronic unit to excite an oscillation in cooperation with the sensor coil, with an oscillation with a specific frequency being generated as a function of the parameters of the oscillator and the sensor coil and the sensor coil establishing a magnetic field.

Various measuring tasks may be performed by a method in accordance with the present invention. For example, it can be used for determining the positions of moveable rods, pins, shafts or housing components.

Use in automated manual transmissions or for the determination of the position of a clutch component is especially desirable.

Further preferred uses may be the determination of the position of an hydraulic cylinder, gear rack, linear drive and other part, provided that the latter's location or position can be detected by means of an indication of a displacement-dependent parameter of a target object.

The method may be configured in such a way that such an indication is carried out continuously in relation to an actual position of the target object.

Since a method in accordance with the present invention may involve the influencing of an oscillating circuit by means of a metal object, oscillation parameters may be selected in such a way that the sensor does not only respond to ferromagnetic materials but also to any other metal materials. Thus, ferromagnetic materials, more especially for the coils, can even be omitted.

One embodiment of the method of the present invention may provide that the sensor is equipped with means to perform a switching function. This means that the sensor outputs a signal value when the target object reaches a specific position.

The sensor coil may work in combination with an oscillator which forms part of a microcontroller, whereby the resulting oscillating circuit is excited and oscillates at a frequency to be selected according to the specific application.

In order to keep the oscillating frequency sufficiently stable, the microcontroller may additionally be equipped with a voltage regulator and a temperature compensation circuit.

The field strength changes caused by the target object likewise may cause a change in the resonance frequency at which the oscillating circuit operates. Via an evaluation circuit which also may form part of the microcontroller, variations in nominal frequency can be determined and the respective measuring values and/or information transmitted to the actual microcontroller module. By means of a permanently stored programme, the latter may detect and evaluate the measuring values of the evaluation unit and output them via the output circuit.

The supply voltage of the sensor can be provided by a connector. The output signals of the microcontroller can likewise be transmitted by the same or another connector.

In a further embodiment, a common housing of a position sensor can be extended by means of a housing on both sides in the area of the target object, with the target object being axially guided within the housing. In combination with a compression spring disposed within the housing, freedom from play is ensured. A guide bushing arranged at the other end of the target object may serve for the precise, concentric guidance thereof.

In a further embodiment in which the system is not capable of providing a target object in the right geometry, location or material, a spring-loaded target object may be accommodated and enclosed as an integrated sliding object within the sensor housing by extending the housing, more especially the plastic encapsulation, by a tubular section, with the integrated sliding object being guided through an element which can be placed on either side of the tubular element. The target object may remain located on the outside of the encapsulated PCB portion, thus causing a closed and, more especially, sealed system for the electronics portion. A compression spring may ensure the continuous contact with an actuating mechanism of the system which, for example, may be a plunger or a cam.

The printed circuit board carrying a microcontroller may either be identical with a multilayer printed circuit board which forms the sensor coil, or it can be incorporated into an additional extension of a housing as a separate printed circuit board.

In a preferred embodiment, the sensor with further individual parts described above may be accommodated as a compact unit in a common housing.

Especially preferably, the sensor coil is encapsulated in a plastic housing and a sensor shaft, when in use or forming part of the sensor, is closed and, even more preferably, sealed, which means that, for example, oil can flow around the target object, namely in both applications, that is when the sensor shaft is in use, but also when detection or measurement takes place by means of the shaft. This means that, in applications of a PCB, the electronics, and the coil within the plastic housing are sealed in such a way that there is a closed system.

Examples of an eddy current sensor, and a method of using an eddy current sensor, embodying the present invention will now be described in greater detail with reference to the accompanying drawings, in which: Figure 1 shows an axial sectional view of an eddy current sensor constituting a first embodiment of the present invention; Figure 2 shows a rear view of the sensor shown in Figure 1; Figure 3 shows an axial sectional view of a modified form of an eddy current sensor constituting a second embodiment of the present invention; Figure 4 shows a an axial sectional view of a further modified form of an eddy current sensor constituting a third embodiment of the present invention; and Figure 5 shows a block circuit diagram of the electronic circuitry of the embodiments shown in Figures 1 to 4.

A method according to the present invention may be carried out using an eddy current sensor comprising a position sensor 1 which cooperates and/or interacts with a measurement object / transducer element 2 as shown in Figures 1 and 2.

The sensor comprises at least one electronic unit cooperating with a sensor coil 3, and an electronic connector 4 serving to provide a supply voltage and transmitted signals. The aforementioned components are combined in a common housing 16. The housing 16 can be shaped in a customary manner.

The mode of operation of the eddy current sensor comprises activating at first the electronic unit arranged in the sensor by applying an operating voltage. An oscillator 11 (shown in Figure 5) present in the electronic unit excites an oscillation in cooperation with the sensor coil 3, with an oscillation with a specific frequency being generated as a function of the parameters of the oscillator 11 and the sensor coil 3, so that the sensor coil 3 establishes a magnetic field.

A measurement object / transducer element 2 is located in the vicinity of the sensor coil 3 and is moved, thus changing the field strength in the area of the coil 3 and, at the same time, the frequency of the oscillating circuit constituted by the sensor coil 3 and the oscillator 11. By means of an evaluation circuit 14 (also shown in Figure 5), these changes are detected and converted into measured variables suitable for further processing. The information obtained is transmitted by the evaluation circuit 14 to a microcontroller 13. The latter processes the information obtained using, inter a lia, a stored programme sequence and develops therefrom control signals which can be further processed in external devices. An output and protection circuit 15 is disposed in the electronic unit for trouble-free operation.

In order to ensure a stable operation and meet the required measurement conditions, a voltage regulator 12 is further assigned to the electronic unit, and is connected between the oscillator 11 and the evaluation circuit 14.

Furthermore, a specific feature of the eddy current sensor is that the sensor coil 3 comprises a plurality of coils constructed in a planar manner.

The method can be such that a path measurement is carried out continuously in relation to an actual position of the measurement object / transducer element 2.

In a further embodiment of the path measurement method, when specific parameters are reached, a switching function according to the characteristic of a so-called threshold value switch can be provided, depending on specific parameters reached in the oscillating circuit constituted by the oscillator 11 and the sensor coil 3.

A path measurement method with a sensor in accordance with the present invention in which the measurement object / transducer element 2 has geometrical irregularities is especially preferred. This means that the measurement object / transducer element 2 is present in the area of the sensor coil 3 but can change its position and thus the cross section of the part of the element closest to the coil 3 changes.

Preferred embodiments of such changes in cross section are annular grooves, bores, one-sided flat portions or varying materials.

A further embodiment of the path measurement method may be that a part comes close to the sensor coil 3.

In an especially preferred embodiment of the path measurement method, the measurement object / transducer element 2 has a cross-sectional area with a continuous transition from a small diameter to a larger diameter, thus enabling a quasi-analogue determination of position.

Furthermore, the measurement object / transducer element 2 can have a part 5 by which it is in contact with or connected to a part to be monitored or measured.

Various measuring tasks can be performed by a path measurement method in accordance with the present invention. For example, it can be used for determining the position of a moveable rod, pin, shaft or housing component.

The use in automated manual transmissions or for the determination of the position of a clutch component is especially preferable.

Further preferable uses may be the determination of the position of an hydraulic cylinder, gear rack, linear drive and other part, provided that the latter's location / position can be detected by means of path measurements.

As already described above, the sensor comprises at least one sensor coil 3, one electronic unit and one housing 16.

In accordance with the present invention, the sensor coil 3 comprises a plurality of coils constructed in a planar manner, with the planar coils each being located on a carrier medium.

Thus, by choosing an appropriate number of such coils constructed in a planar manner, the inductance of the sensor coil 3 can be determined over a wide range, whereby, in cooperation with the oscillator 11 disposed in the electronic unit, the possible operating frequency can also be adjusted over a wide range.

An individual planar coil can be implemented in such a way that, as a single element, it has as large an inductance as possible. In this way, the number of planar coils to be combined with each other can be minimized.

A preferred embodiment may be that respective planar coils are arranged on the two sides of a double-sided printed circuit board.

A further preferred embodiment of the sensor coil 3 is implemented if the planar coils are integrated within a so-called multilayer printed circuit board and more than two planar coils can thereby be interconnected.

Apart from the possibility of adjusting the inductance of the sensor coil 3, a sensor coil 3 having a stable structure is produced by an embodiment in accordance with the present invention, which does not require any additional measures for its protection.

The position sensor 1 in accordance with the present invention can be developed further in accordance with various operating conditions. Thus, in one embodiment, the measurement object / transducer element 2 can be disposed in a sleeve 8. In this way, it is largely protected against environmental influences.

A compression spring 7 which can ensure continuous contact of the part 5 with a part to be monitored or detected can be assigned to the measurement object! transducer element 2.

The part Scan be guided centrally by means of a guide 6 in the form of a ring.

In a further embodiment in which the system is not capable of providing the measurement object 2 in the right geometry, location or material, a measurement object 2 spring loaded by a compressing spring 7 can be accommodated and enclosed as an integrated sliding object within the sensor housing 16 by extending the housing, more especially the plastic encapsulation 16, by a tubular section 8, with the integrated sliding object being guided through the guide 6 which can be placed at one end of the tubular element 8 as shown in Figure 3. The measurement object 2 remains located on the outside of the encapsulated PCB portion, thus causing a closed and, more especially, sealed system for the electronics portion. The compression spring 7 ensures a continuous contact with the actuating mechanism of a system which, for example, can be a plunger or a cam.

In cases where the arrangement of the electronic unit on the printed circuit board of the sensor coil 3 is not possible, an additional printed circuit board 9 as shown in Figure 4 can carry this electronic unit and be connected to the sensor coil 3.

Thus, the illustrated embodiments of the present invention have the advantage that they allow for carrying out a path measuring method using a sensor with a sensor coil comprising a plurality of individual planar coils, wherein the sensor can be used over a wide range of parameters, whilst being robust and inexpensive to produce.

List of reference numerals 1. 1 position sensor 2. 2 measurement object / transducer element 3. 3 sensor coil 4. 4 connector S. 5 part 6. 6 guide 7. 7 compression spring 8. 8 sleeve, housing, tubular section 9. 9 printed circuit board 10. 10 coil 11. 11 oscillator 12. 12 voltage regulator 13. 13 microcontroller 14. 14 evaluation circuit 15. 15 output and protection circuit 16. 16 housing

Claims (20)

1. Claims: 1. A method of using an eddy current sensor to provide an indication of a displacement-dependent parameter of a target object, by interaction between the target object and the eddy current sensor, wherein the eddy current sensor comprises an electrical connector and a sensor coil, and in which the following steps are performed: by applying an operating voltage, a magnetic field is built up by an oscillator in cooperation with the sensor coil, the target object is moved in the vicinity of the sensor coil through an opening in the sensor coil, whereby the field strength in the area of the coil and the oscillator changes, and the changes which occur are detected by an evaluation circuit and transmitted to a microcontroller, the microcontroller processes the signals of the evaluation circuit and provides the latter with said signals via an output and protection circuit, wherein the sensor coil comprises a plurality of windings constructed in a planar manner.
2. 2. A method according to claim 1, characterised in that such indication is carried out continuously in relation to the position of the target object or as a switching function, depending on specific parameters present in the oscillating circuit.
3. 3. A method according to claim 1 or claim 2, characterised in that the target object has a varying geometry and/or a portion with a continuously changing cross section.
4. 4. An eddy current sensor for providing an indication of a displacement-dependent parameter of a target object, by interaction between such an object and the eddy current sensor, comprising a sensor coil which interacts with such an object, and an electronic connector, wherein the sensor coil has a plurality of windings constructed in a planar manner, and wherein the sensor coil has an opening through which such an object can be moved axially.
5. 5. An eddy current sensor according to claim 4, characterised in that the eddy current sensor includes such a target object.
6. 6. An eddy current sensor according to claim 5, characterised in that the measurement object has a varying geometry and/or a portion with a continuously changing cross section.
7. 7. An eddy current sensor r according to claim 6, characterised in that the measurement object has a conical shape.
8. 8. An eddy current sensor according to any one of claims 5 to 7, characterised in that the target object has a part by which it is in contact with or connected to an object to be detected.
9. 9. An eddy current sensor according to one or more of claims 5 to 8, characterised in that the measurement object is disposed in a sleeve or in a housing or in a tubular section.
10. 10. An eddy current sensor according to claim 9, characterised in that the target object is three-dimensionally supported in the sleeve or in the housing or in the tubular section.
11. 11. An eddy current sensor according to one or more of claims 5 to 10, characterised in that a resilient structure is applied to the target object.
12. 12. An eddy current sensor according to claim 11, characterised in that the resilient structure is a compression spring.
13. 13. An eddy current sensor according to one or more of claims 4 to 12, characterised in that the eddy current sensor is provided with a printed circuit board.
14. 14. An eddy current sensor according to one or more of claims 4 to 13, characterised in that it comprises a housing which encloses the sensor coil, the target object and an electrical connector.
15. 15. An eddy current sensor according to any one of claims 4 or 14, characterised in that the windings of the sensor coil constructed in a planar manner are each arranged on a carrier.
16. 16. An eddy current sensor according to claim 15, characterised in that the windings of the sensor coil constructed in a planar manner are integrated within a multilayer printed circuit board.
17. 17. An eddy current sensor according to any of claims 4 to 16, characterised in that the eddy current sensor further comprises an oscillating circuit connected to the sensor coil and an evaluation circuit for detecting the parameters of the oscillating circuit.
18. 18. An eddy current according to one or more of claims 4 to 17, characterised in that the eddy current sensor is provided with an electronic unit which contains a microcontroller by means of which values of the evaluation circuit can be processed and outputted to an output and protection circuit using a stored programme.
19. 19. A method of using an eddy current sensor substantially as described herein with reference to and as illustrated in Figures 1, 2 and 5, with or without the modifications shown in Figure 3 or Figure 4, of the accompanying drawings.
20. 20. An eddy current sensor substantially as described herein with reference to and as illustrated in Figures 1, 2 and 5, with or without the modifications shown in Figure 3 or Figure 4, of the accompanying drawings.