DE102007055155A1 - Sensor structure e.g. brake disc, speed and direction measuring device for e.g. motor cycle, has planar coils, where each coil has breadth corresponding to tooth module of sensor elements and is connected with evaluation circuit - Google Patents

Abstract

The device has rectangular planar coils (2.1, 2.2) arranged adjacent to each other in a plane on a carrier (5), where each coil has a breadth corresponding to a tooth module (M) of sensor elements (8) to be measured. The coils are connected with an ohmic resistor and a controllable switch element in rows. A controller switches on and switches off current through the coils in a time-controlled manner. Each of the coils is connected with an evaluation circuit in an electrically conductive manner for measuring inductive reciprocation with the sensor elements. An independent claim is also included for a device for measuring variable reciprocation between an electromagnetic field of a coil and a structure, which is made of electrically conductive and ferromagnetic material.

Description

The The present invention relates to a device for inductive, contactless Measuring the rotation of a gear or a brake disc with planar Coils on a sensor head to a stop, with a resolution up to to fractions of tooth module 1 regardless of the distance. The measurement takes place with two small, planar coils even over a few millimeters, being that in one device or a machine existing gear or a brake disc with regular holes as Encoder can be used. The measurement can also be in linear Arrangements are made. With the clock control and differential Evaluation circuit, the measurement takes place bimodal from the standstill of the encoder up to higher Frequencies with current pulses changeable Duration and phase angle, and uses the feedback differently induced Eddy currents. With a single coil, it is possible, the distance inductive to determine very accurately by making the measurement differential for different pulse durations carried out and a measurement type serves as a reference.

she is applicable as a replacement of known inductive proximity switches as well as incremental encoders of industrial metrology or Wheel sensors in the automobile, and has a mechanical and electronic conceivably simple construction. In a further embodiment of the sensor, The planar coils are on the outside of a high strength ceramic arranged so that the thickness of this protective ceramic is not to the distance contributes to the donor and the measurement even at high pressures and temperatures in aggressive Environments can be done.

In known devices for inductive measuring of the distance and Encoders are used with coils and capacitors or resonant circuits Manufactured oscillators, their quality, amplitude or frequency through the approach a donor element to the field of the coil and the associated Eddy current losses slightly to be changed.

Of the obvious disadvantage of these solutions is that this change the voltage of the resonant circuit is very small in relation to Amplitude and with increasing distance quickly in the range of tolerances the electronic components disappears. Improvements to this Employ systems Therefore, usually with the improvements of the precision of the oscillator.

In simple designs In addition, the measurement at standstill is not directly feasible, or the Distance between sensor coil and encoder is considerable expense preferably made small and kept constant. In addition, the possible working distance reduced by the thickness of the protective housing. If the distance in the work area is variable, all known Encoder limited to the determination of 1 clock per donor element and achieve only the resolution of tooth module 2 in safe operation, without Direction detection. For arrangements in which the distance is proportional is the rotational position, the achievable accuracy due to the principle nonlinearities questionable anyway.

Other Solutions, like magnetic pole wheels work over too slightly longer distances with good Resolution. An obvious disadvantage now is that the costs for one magnetic encoder and sensor are quite high. Added to this is the sensitivity against high temperatures and mechanical loads as well as the tendency ferromagnetic dusts to collect in their environment. This also leads to incorrect measurements over the Lifespan and limitations in use.

task It is therefore advantageous for the present invention to have a sensor arrangement form, with which the rotation of a pole wheel or linear Encoders to standstill inductive and contactless up to about 1/16 of the tooth module 1 is determined at a distance of at least 2 mm and the Influence of the changeable Distance in the work area is compensated, with the diameter the planar sensor coil corresponds approximately to the tooth module to be measured, So in module 1 is only 3.5 mm.

On a flat substrate are two planar coils with 4 or 5 turns next to each other, a width of about 3.5 mm and a length of about 5 mm next to each other arranged. For the tooth module 1 is the distance between the centers 1 module plus 180 °, ie 6/4 M or 4.7 mm, and the shape is largely rectangular. The pole wheel with tooth module 1 has with his teeth a distance of 1 to 3 mm to the coils, can be left or be turned right and consists of a ferromagnetic or electrically conductive Material. It can also be a linear encoder used. Of the Distance between teeth or module now corresponds to a period and the relative Position of the left coil to the sine and that of the right to the sine of φ + 180 °.

Each of the two coils is connected via an electrically conductive connection, such as a conductor, a connector or a cable to the evaluation circuit. Each coil is connected in series with an ohmic resistor and a switching element. The ohmic resistance limits the current in the switched-on state and over the Switching element, the current of each coil can be individually switched on or off by a controller.

Of the Current through the coil generates an electromagnetic field with a certain energy. In case of change the current by switching on and off are induced in electrically conductive materials eddy currents and the energy of the magnetic B field of a coil is reversed in the switching process reduces the amount of energy of the eddy currents and measurable. Here is the size of this eddy currents square proportional to the distance between the conductors the coils and the conductive Area, the surface of the pole wheel, and according to the law of induction, the duration of the switching operation. In addition, the eddy current develops its own B-field, which is the Spool is opposite and sounds only after some time off. Therefore the influence on the B field of the coils to be measured is also dependent on the time between switching on and off the coil current.

moreover the coils will be adjacent and dependent on the direction of the currents the B-fields of the coils in the adjacent part are added or subtracted. By simultaneous switching, or opposite switching on and off and time-shifted switching will continue to induce eddy currents controllable. Through the chronological sequence of switching on and off the streams through the coils, the electrodynamic interaction with the Eddy current and the overlay The B fields are used to work with the same coils in the same Geometry independent of each other Perform measurements in rapid succession.

He follows now a 1st measurement with a very short duration between on and off Turn off the coil current and so that only one coil is energized is, so is the retroactive effect of the induced eddy current much stronger than in a second measurement with simultaneous switching of the current in both coils, because the coil currents in the adjacent part are guided in opposite directions both coils act like a bigger one, that to the donor elements has a phase angle of 90 °, ie the cosine. By the comparison of the 1st and the 2nd measurement can be as the rotational position be determined much more accurately, regardless of the distance between Sensor head and encoder, respectively the evaluation takes place differentially and it can bigger reinforcements be safely used.

If the angle within a period between the sensor head and the sensor element Zero is an encoder element and the left coil to optimally Cover. In this position, eddy currents are optimally induced. In the Movement about half a period further, is the induction of eddy current minimal. As the rotation progresses, a periodic waveform is created which corresponds approximately to a sinewave. The amplitude of this signal is very strong and nonlinear depending on the distance and that of the actual B field of coil superimposed. By the arrangement of the second coil with an offset 180 ° in the period corresponds to the module to be measured, a waveform is generated, which corresponds to the negative sine.

By Subtraction of the measurement of the left coil from the right becomes the DC component removed from the signals and by dividing sinewave with the cosine, the angle can be independent of the amplitude of the Signals are determined. The accuracy is limited only due to the required dynamic range and the available resolution of a Analog to digital converter. For example, between 1 and 3 mm observed a signal swing of 60 mV down to 1 mV for tooth module 1. With a reinforcement by a factor of 10 and an ADC with 1 mV resolution, the angle can be up 1/16 of the period, that is about 20 ° determined be without exact knowledge of the distance.

The Energy of the B fields of the coils and the influence of the losses through the eddy currents is determined with a novel circuit. By the described Series connection of resistor and inductor becomes a certain current imprinted, the coil being directly connected to a supply voltage on one side is. The switching off of this current takes place with real switches finite switching speed and generates according to the law of induction Voltage pulse proportional to current, inductance and switching speed. At the other terminal of the coil, a capacitor is now attached, the over a diode in the flow direction with another capacitor, the Measuring capacitor, is connected. The voltage pulse now causes a Voltage rise on the capacitor on the coil, so that with the Flow of charge carriers over the Diode in the measuring capacitor a current arises. If parasitic effects are neglected at first so the time course of the product of voltage pulse and current the energy of the B-field the coil that charges the measuring capacitor up to the voltage at the the energy corresponding to its capacity corresponds to that of the coil. This will be first the energy of a coil as a voltage across a capacitor for some Time measurable. The advantage is that the duration of the switching process of transistors can be very short and this very high dl / dt acts as a reinforcement. Despite the very low inductance, a few volts signal swing achieved and by eddy currents caused changes of the B-field, so easy and fast measurable.

Before switching off, it is advisable to turn on the power first. The currentless coil and the first capacitor are briefly brought to the ground potential of the switch. The other side of this coupling capacitor now has a negative potential, which is compensated by the influx of charge carriers via another diode to ground. As a result, charge carriers are again available for charging the measuring capacitor at the next switch-off and several such pulses can be executed one after the other and lead to a further amplification of the measurable voltage.

Actually follows this gain over several Pulses empirically of an e-function, asymptotic against a limit, which corresponds to the voltage of the turn-off pulse of the coil.

Around To establish a defined initial state, it is appropriate to the Measuring capacitor over to discharge another switching element before the measurement. However, shows the practical exam, that also the continuous, low discharge over a very high parallel resistance good signal level and dynamics achieved.

Becomes this circuit for each provided a coil, the difference of the voltages to the Measuring capacitors analog further amplified and measured. in the Trap of the encoder with direction detection are so measurements with simultaneous and separate energization required. Especially advantageous It is there that fluctuations in component tolerances and changes in the temperature range, such as the switching behavior of the transistors, be very well compensated.

The Circuit can also be advantageously extended so that the two Measurements with different duty cycles for only one Coil directly analog possible becomes. To do this, the diode, over which the charge balance is provided with a switch so that over the Control the charge balance can be switched on or off. In order to the charging of the measuring capacitor is switched on and off.

bring one this "measuring circuit" from capacitors, Diodes and switches a second time, parallel to the first at the Coil on, so can short pulses in one and longer be stored in the other and are thus directly differentially measurable. It is particularly advantageous that by this bimodal measurement the critical switch of the coil current is the same for both measuring circuits acts and tolerances are compensated so well.

moreover It is advantageous if between supply voltage and coil another switch inserted becomes. This allows a second coil with its own switch in parallel attached to the first coil and the coils so from the controller be multiplexed. The result is a further improvement stability and therefore the accuracy of the measurement.

is the measurement of the distance required with only one coil, so can the second, electrically identical coil is arranged and multiplexed in this way be that change the environment does not look or act differently on them. This can still disturbing further compensated and the accuracy of the measurement can be increased. Or the reinforcement will be raised, around the range, or resolution to improve.

These The object is achieved with the characterizing parts by the claims (1) and (6) solved. Advantageous embodiments of the device according to the invention will become apparent from the measures in the dependent Claims.

The inventive arrangement two planar coils and the electronic evaluation circuit Compared to previously known solutions has the advantage that it the mechanical structure is simpler and less expensive, large coils and Ferrite cores omitted.

Farther It is advantageous that this arrangement with two small planar Coils provides a significant improvement in geometric resolution and the measurement can be made fully differential, or the planar coils are brought closer to the measuring location as part of the housing can.

It is also advantageous that the arrangement with both encoder elements made of ferromagnetic materials, as well as those of electrical conductive Material or coating works.

Of the particular advantage of the evaluation circuit according to the invention exists in that a coil, or a combination of electrically identical coils, bimodal is measured and a 1st type of measurement as a reference for the 2. Measuring mode 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 a 3D sketch of a carrier with two rectangular planar coils on the top, the centers are arranged at a distance of about 1 + 2/4 tooth modules, and a circular pole Rad with encoder elements, which are arranged at a distance of one tooth module and which is rotatable so that between the carrier with the coils and the encoder elements, a relative movement in the direction X, and vias and connections for the electrical connection to the transmitter;

2 two planar circular coils arranged in 3D view on the top and bottom of the carrier, a cover for mechanical protection above the coil on the top, their electrical connections and a linear element with a hole as a donor element;

3 a planar circular coil in 3D view on the support element, another support structure with electrical connections to the first and another planar coil, which is largely unaffected by donor elements in this arrangement, and a donor structure;

4 the electrical evaluation circuit in a first embodiment with a donor structure in interaction with two coils, each of which is conductively connected to the supply voltage and connected in series with an ohmic resistor and a controllable switching element, and in each case a coupling capacitor, two diodes, the charge carrier flow in the conduct positive switch-off pulse to the measuring capacitor and charge the coupling capacitor again at the negative switch-on and thus make the measuring voltage on the measuring capacitor regardless of the supply voltage, and a parallel resistor or another switching element for discharging the respective measuring capacitor and the electrically conductive connection to the controller, and some exemplary pulse sequences with which the controller turns on or off the current through the coils;

5 a further exemplary arrangement of two rectangular coils with a distance of 6/4 tooth module in the 3D view and a linear encoder structure with holes spaced by 1 tooth module, as well as an exemplary eddy current and the superposition and interaction of B fields;

6 a further embodiment of the electronic evaluation circuit with a coil, wherein the two measuring circuits of capacitors and diodes connected in parallel and extended by a respective switching element which controls the inflow of charge carriers in the coupling capacitor to conduct measurements with different pulse durations in each measuring capacitor, so that the measuring voltages are simultaneously available analogue;

7 a further embodiment of the electronic evaluation circuit with a further coil and in each case an additional switching element between the supply voltage and coils for time multiplexing of the coils on the evaluation circuit and in each case a further diode in series with the coil to the return flow over the most commonly present in FET substrate diode to stop;

In 1 is a first embodiment of the inventive arrangement with two identical as possible, planar, largely rectangular coils ( 2 ) on the top of the carrier ( 5 ). The spools ( 2 ) have several turns and their centers have about 6/4 of the distance (M) of the donor elements ( 8th ). In the middle of the coils ( 2 ) is a via via which together with a conductor track ( 7 ) the electrical conductive connection to the four mechanical and electrical connection elements ( 4 ) will be produced. In this case, the carrier ( 5 ) a thickness corresponding to the application (d) and can be applied to a sleeve ( 6 ) can be arranged. The carrier ( 2 ) can be high strength, a printed circuit board or even flexible, is characterized in that it consists of an electrically non-conductive material. A gear ( 1 ) with encoder elements ( 8th ), here exemplary teeth in trapezoidal shape with the distance from a tooth module (M), is at a distance (h) above the carrier ( 5 ) rotatably arranged so that its rotation a relative movement between the donor elements ( 8th ) and the two coils ( 2 ) generated in the direction X over. The direction X corresponds to the connecting line of the centers of the two coils ( 2.1 . 2.2 ) and the arrangement may be radial, tangential or axial. This relative movement in X is to be measured with an accuracy which, depending on the distance (h), detects at least the movement about a tooth module or fractions thereof and the direction of rotation. Fractions of the tooth module (M) are given as angles and the distance of the encoder elements ( 8th ) is considered as a period. Let the angle be 0 °, if an encoder element ( 8th ) with the center of its surface just above the center of the left coil ( 2.1 ) stands.

These Encoder structure may also be a brake disc or impeller.

2 shows two round, planar coils ( 2.1 . 2.2 ) in the 3D perspective on top of each other or underside of the carrier ( 5 ), optional sleeve ( 6 ) and electrical connection elements ( 3 . 4 . 7 ). In addition, the thinnest possible protective element ( 11 ), which is the top of the carrier ( 5 ) and the coil ( 2.1 ) protects against mechanical and chemical stresses from the environment. Above this, at the distance (h), there is an indicated linear encoder structure ( 9 ) with at least one electrically conductive or ferromagnetic surface, or of such material, and a bore as a donor element ( 8th ). Measure the distance (h) to the coil ( 2.1 ) on the top, or the distance (h + d) to the coil ( 2.2 ) on the underside, which is used here as a reference with the known additional distance (d). A feed in the direction of X can also be measured, but without distinction between left and right.

3 additionally describes by way of example the arrangement of only one coil ( 2.1 ) on the top of the carrier ( 5 ). Via the permanent or detachable electromechanical connections ( 4 ) this coil is ( 2.1 ) with another carrier ( 10 ) electrically connected, on which another, as similar as possible shaped coil ( 2.2 ) and the evaluation circuit are located. This coil ( 2.2 ) is arranged so that the relative movements of donor elements ( 9 ) As far as possible do not affect their electromagnetic field and so can serve as a reference in the measurement of the distance (h) or other variables, such as conductivity of the encoder or the presence of cracks and layer thicknesses. 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 or ceramic substrates only have the advantage of good geometrical reproducibility in the cost-effective production process.

4 shows an exemplary circuit diagram of the evaluation circuit according to the invention with the encoder structure ( 1 ), the coils (L1, L2), each connected in series with an ohmic resistor R and a FET (T1) as a switch. The controller (S) generates a time sequence of switching on and off, which are indicated as pulse trains (S1, S2) and correspondingly on the geometry of the coil (L) with the encoder structure ( 1 ) and change the energy contents of the B fields of the coils (L) to be measured. When switching off the current with a switching element (T1) creates a positive voltage pulse with a voltage proportional to the switching speed dl / dt. Via the coupling capacitor (C1) this causes the flow of charge carriers via the diode (D1) into the measuring capacitor (C2) until the voltage (U) corresponds to this pulse voltage or the voltage at the coupling capacitor (C1) is adjusted by the outflow of the charge carriers. Neglecting parasitic losses, the electrical energy of the measuring capacitor (C2) corresponds to the energy content of the electromagnetic coil field and is thus directly measurable as voltage (U). In particular, this voltage also corresponds to the number of pulses measured so that the gain can be further adjusted by the number of pulses given known capacitance.

To it is necessary that when turning on the switch (T1) the Coupling capacitor (C1) again charge carriers are supplied via the diode (D2), until its tension is balanced. This is possible because at power up the voltage of the coil (L) and thus of the coupling capacitor (C1) short is placed to the potential of the switch (T1) until a current through the resistor (R) flows. In order to is the potential of the other side of the coupling capacitor (C1) according to the previously discharged charge of negative, charges flow over the Diode (D2) while Diode (D1) from the reflux the measuring capacitor blocks.

In accordance with the often low interaction between coil (L) and encoder structure ( 1 ), the measured voltage (U) is relatively high and the amplitude of the change is relatively small. Due to the double execution, this offset can be subtracted analogously in the control and the difference of the voltages can be further differentially amplified by known means. If this measurement is now carried out once with simultaneous switching of the coils (L), then this difference of the voltages (U1, U2) corresponds to the cosine, while it corresponds to the sinus with time-shifted switching.

Especially It is advantageous that in this sequential, bimodal Measurement of all components equal and ultimately only the different generation the eddy current is effective. This is considerably more accurate measurements possible in comparison to the prior art. Also carry the very small inductors to a much higher measurement sequence at, so that the dynamics by about a factor of 10 to 100 is higher. The current strength in the pulse through the coils is on the order of only 1 mA to about 100 mA.

Of the Parallel resistor (Ry) is used to discharge that over one another switching element (T4) are also accurately controlled in time can to bring the measuring capacitor in the defined initial state. Advantageous are all these extensions, up to an analog-to-digital converter and the flow control integrated in a circuit. The edition the measured clock and the direction of movement takes place with known Means.

5 shows an exemplary arrangement of the two rectangular coils (L1, L2), side by side with the distance 6/4 M of their centroids in a plane, and at a small distance (h) the indicated donor structure ( 1 ) with holes (A). This encoder structure ( 1 ) can be linear or a disk, the holes (A) axially or radially, possibly on the circumference, be arranged. It is important that here the coils (L) are wound in the same direction and are energized opposite. In the area in which the coils (L) adjoin one another, the B-field (B12) of the currents (IL1, IL2) is superposed by almost canceling each other out. With simultaneous switching on and off of the currents (IL), a greatly reduced induction of eddy current (Iw) thus takes place in this region. In the other segments of the two coils (L), on the other hand, the current direction agrees very well, so that both coils (L) induce an overall eddy current (Iw) which corresponds to their common area and also to the underlying sensor elements (FIG. 8th ) interacts completely.

The encoder elements ( 8th ) influence the formation of eddy current (Iw) directly, as is well visible in coil L1 when energized alone. Are the centers of bore ( 8th ) and coil L directly on top of each other, so a circular eddy current (Iw) can be formed when switching on or off and thus withdraws energy from the magnetic B field of the coil. In addition, its B field is opposite to that of the coil, so that this is reduced again and a dependence of the strength of this interaction of the distance (h) with the fourth power arises. If coil and encoder elements, in this case coil L2 and bore A2, do not coincide, the bore acts as an insulator and prevents the formation of an eddy current to a certain depth. Accordingly, the field of the coil L2 is weakened less.

In the experiment it has been proved that this interaction during feeding of the encoder structure ( 1 ) can be measured in the direction X as a sinusoidal curve, if the difference between L1 and L2 is measured with the evaluation circuit, provided that in each case only one coil is energized and measured alternately. If the measurement is carried out simultaneously, then a cosinusoidal course can be measured, the period being the distance (M) of the donor elements ( 8th ) corresponds.

If tooth-like structures are used as donor elements ( 8th ), so the physics is different, but it is the same result with about 30% lower differential voltages (U) to observe.

6 shows a further embodiment of the measuring circuit according to the invention with a coil (L) and a transmitter structure ( 1 ). The measuring circuit (C1, D1, D2, C2) is designed in duplicate and connected in each case via the coupling capacitors (C1.1, C1.2) to the coil (L1). An additional switching element (T2) now controls the inflow of charge carriers when switching on. If no charge carriers flow, the switch-off pulse does not contribute to the measuring voltage (in the case of real FETs, the voltage is nevertheless lowered sufficiently). Thus, different pulse sequences can be directed to one (C2.1) or another (C2.2) measuring capacitor and the small differences in voltage can be measured differentially. This is advantageous in order to detect distances and rotation when the detection of the direction of rotation is not required, or for the measuring task only one coil is available.

7 shows the measuring circuit according to the invention with a coil (L2) connected in parallel to the first (L1). With a further switching element (T3.1, T3.2) between the supply voltage and the coils (L), these can now be multiplexed and these measurements can be carried out for each coil. The diode (D3), each connected in series with a coil (L) only prevents the return flow via the integrated substrate diode real FETs as a switching element (T3) at the voltage pulse of the shutdown.

This second coil (L2) has as far as possible the same electrical properties as the first (L1) and is completely outside the influence of the encoder structure ( 1 ), or with a defined change, such as the distance (h) increased by the thickness (d) of a beam. Thus, this coil (L2) serves as another reference and all tolerances and thermal influences can be almost completely compensated.

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 the novel measuring method and the size of the eddy currents can be experienced as a change of the measuring voltage Uc on the measuring capacitor. The energy of the coil field is used as a current-voltage pulse to charge the measuring capacitor. The relationship between the field of the coil and the measuring voltage describes the negation of parasitic losses the formula for the energy of the charge of a capacitor: e C = ½ · C · U C 2 = E L (3) and after forming: U C 2 = 2 · E L / C (4)

This voltage is used for the two coils ( 2.1 . 2.2 ) acc. 1 with the circuit gem. 4 for the functionally identical coils (L1, L2) be is correct, whereby the measurement of the pulses does not take place simultaneously and successively. According to the relative position between encoder elements ( 8th ) and the coils ( 2.1 . 2.2 ) eddy currents are formed and measurable, which are determined empirically: U C1S = O + a · sin (φ) (5) U C2S = O - a · sin (φ) (6)

In this case, O describes the offset or the fundamental voltage of the measurement and a the amplitude of the oscillation over a full period. By subtraction results U C1S - U C2S = 2 · a · sin (φ) (7) independent of the offset. In another measurement, the pulses are generated simultaneously and successively. According to the relative position between encoder elements ( 8th ) and the coils ( 2.1 . 2.2 ) eddy currents are formed, partly superimposed and thus measurable, which are determined empirically as: U C1C = O + a · cos (φ) (8) U C2C = O - a · cos (φ) (9)

By subtraction results U C1C - U C2C = 2 · a · cos (φ) (10)

By further inserting (7) into (10) and simple forming results φ = arctan ((U C1S - U C2S ) / (U C1C - U C2C ) (11) whereby the angle is determined independently of the amplitude of the signals. Thus, the inductive determination of the angle within a period of the encoder elements ( 8th ), regardless of the distance h, which determines the amplitude and free of dynamic thresholds, ie to a standstill. As long as the sampling theorem is not violated, ie the measurements are at least twice as frequent as the frequency of the encoder elements ( 8th ) is to the coils, per tooth module one clock per period and z. B. a 90 ° clock for the direction of movement are generated by the controller. Similarly, a fairly accurate multiplication of these clocks is easily possible if the change in the angle between two samples, or the last generated clock is evaluated. At one cycle per 20 ° angle change since the last cycle, this corresponds to 16 cycles per tooth module.

Especially It should be emphasized that here the tooth module is used because he In technical applications with gears, etc. is a known size. Now, of course, that is the "range" of inductive sensors also proportional to the diameter of the coils, especially at planar coils. Dependent from the measuring task in the sensor arrangement according to the invention, the diameter the coils and their distance within wide limits increases and be downsized.

A Limit of magnification is then reached when the coil when switching off with parasitic capacitances a Resonant circuit forms. This is not harmful as long as the amplitudes the subsequent vibrations drop quickly, but also unhelpful, because there is a delay until the beginning of the next Measurement required. This is especially necessary if conventional Coils with or without ferromagnetic core and greater inductance for use come.

Farther It is advantageous if the coils are on or in a high strength technical ceramics as a carrier to be ordered. Unlike conventional inductive proximity sensors, always inside a case are attached, can the coils so closer be brought to the encoder structure. At a thickness of the carrier of about 2 mm and a maximum range of about 3 mm with tooth module 1, this is a significant advantage, which will further increase the Number of bars / pole and thus the resolution can be used.

Further embodiments of the sensor according to the invention emerge from the consideration that it is often desirable to determine the amplitude a precisely in order to determine the distance to a transmitter structure (FIG. 1 ) to eat. This measurement takes place z. B. according to an arrangement. 2 and the circuit variant in 6 or 7 ,

With a switch-on, an eddy current is induced into the sensor structure, depending on the distance. According to the conductivity of the encoder structure ( 1 ) this energy is converted into heat over time. If now the measurement of short pulses on one measuring capacitor (C2.1) and the measurement of longer pulses on the other (C2.2), then the different fall of the eddy current and its reaction to the B field of the coil can be determined differentially and is proportional to the distance at constant pulse durations.

Further Refinements with these bimodal multiple measurements are up to Determination of conductivity of the material possible.

A further design options the sensor arrangement according to the invention results when arranging all components on a single carrier. The solution the measuring task is unchanged.

In addition, the circuit according to the invention can be executed several times and recognize, for example, an index pulse as an absolute position or recognize with multiple channels an absolute coding on the encoder structure, such as a Gray code or a recursive binary random code, which allows the absolute position after n clocks 2 ⁿ -1 divisions to be determined. Likewise, the measurement circuit according to the invention can be used to determine changes in the B field of a coil that correspond to other measurement tasks, such as determining the layer thickness of electrically conductive materials, the formation of cracks in surfaces or measuring the conductivity in organic and inorganic materials , as well as the change in relative permeability through interaction with other substances and molecules.

Claims (10)

Device for inductive, non-contact measurement of the speed and direction of a transmitter structure ( 1 ), characterized in that A two coils ( 2.1 . 2.2 ) each having a width which is approximately equal to the tooth module M of the encoder elements to be measured ( 8th ), in one plane on a support ( 5 ) are arranged side by side, wherein the distance between their centers about 1.5 times this module corresponds to M and B, the coils ( 2.1 . 2.2 , or L1, L2), each having at least one ohmic resistance (R1, R2) and a controllable switching element (T1.1, T1.2) are connected in series and C is a controller S, the currents through the coils ( 2.1 . 2.2 , or L1, L2) timed on and off and D these pulses (S1.1, S1.2) are switched after each other simultaneously and in the same direction or for each coil opposite (S2.1, S2.2) are switched to or occur at different times or have different duration and E each coil (L1, L2) with an evaluation circuit for measuring the inductive interaction with the donor elements ( 8th ) is electrically connected. Apparatus according to claim 1, characterized in that A the two coils ( 2.1 . 2.2 , or L1, L2) with all windings on the surface of the carrier ( 5 ), ie are planar, and B the coils through at least one further layer or such body ( 11 ) are covered and mechanically protected from an electrically non-conductive material. Apparatus according to claim 1 or 2, characterized in that A is the evaluation circuit on the same support ( 5 ), or B the evaluation circuit is not on the same carrier ( 5 ) and the electrically conductive connections ( 4 ) are a fixed contact system, or C these electrically conductive connections ( 4 ) Are plugs or sockets of a detachable contact system, or D the electrically conductive connections are made via a flexible cable. Device according to at least one of the preceding claims, characterized in that the encoder structure A consists of an electrically conductive material which by donor elements ( 8th , or A) has regular structures, or B is coated with an electrically conductive material in such a way, or C consists of a material with ferromagnetic properties, which by donor elements ( 8th , or A) has regular structures, or D is coated with a ferromagnetic material such. Device according to at least one of the preceding claims, characterized in that A is the encoder structure ( 1 ) a gear with axially or radially periodically arranged teeth as donor elements ( 8th ), or B the donor structure ( 1 ) a disc with axially or radially mounted holes or holes as donor elements ( 8th ), such as a brake disc in automobile or motorcycle, or C the encoder structure ( 1 ) is linear and a regular arrangement of teeth or holes as donor elements ( 8th ), such as a rack. Device for electronically measuring the variable interaction between the electromagnetic field of a coil and a structure of electrically conductive or ferromagnetic material, characterized in that A at least two coils (L1, L2) according to a supply voltage. 4 connected and with at least one ohmic resistor (R1, R2) and one switching element (T1.1, T1.2) are connected in series, and B in each case via a coupling capacitor (C1.1, C1.2) with the one electrode between Coil (L) and resistor (R) are connected, and via the other electrode, the electrically conductive connection to the anode of a diode (D1) and to the cathode of the diode (D2) is produced, and C the cathode of the diode (D1) with the Measuring capacitor (C2) and the anode of the diode (D2) to the reference potential of switching element (T1) and measuring capacitor (C2) is electrically connected, and D the controller (S), the switching elements (T1) on time and off and with the Messkon E is a parallel resistor (Ry) or a combination of resistor (Rx) and switching element (T4) between measuring capacitor (C2) and reference potential for discharging the measuring capacitors (C2) and the diodes (D1) C2) can be integrated, and F the measurement of the electromagnetic interaction via the difference of the voltages (U1, U2) to the measuring capacitors (C2.1, C2.2) takes place. Device according to claim 6, characterized in that that A first the difference of the voltages (U1, U2) for a certain Sequence of on-off operations (S1) the switch (T1) is determined and after B this difference the voltages (U1, U2) then for a other sequence of on-off operations (S2) the switch (T1) is determined and C these pulse sequences (S) are repeated periodically and D the reinforcement and an analog-to-digital conversion and further evaluation in the controller (S) can be integrated. Apparatus according to claim 6 or 7, characterized in that A according to only one coil (L1). 6 is used and B, the electrodes of at least two coupling capacitors (C1.1, C1.2) of the otherwise same measuring arrangements between coil (L) and resistor R) are electrically connected and C between the reference potential and the diodes (D2.1, D2 .2) in each case a further switching element (T2.1, T2.2) is inserted and D the controller (S) controls these switching elements over time, so that at one of the measuring capacitors (C1.1) the voltage (U1) corresponding to a pulse train (S1) and at the other (C1.2) the voltage (U2) for a second pulse train (S2) are measured differentially. Apparatus according to claim 6, 7 or 8, characterized in that A at least one further coil (L2) of the first (L1) is connected in parallel and B between the supply voltage and the coil (L) each have a further controllable switching element (T3.1, T3. 2) is electrically conductively inserted and C between coil (L), resistor (R) and coupling capacitors (C1) for each coil (L1, L2) a diode (D3.1, D3.2) gem. 7 is inserted so that the coils D can be multiplexed by the controller S. Device according to claim 6, 7, 8 or 9, characterized in that it is a measuring arrangement with one or two coils (L1, L2) in which the energy in the electromagnetic field of at least one coil (L1) is interacting with a mechanically movable one Or that this change is caused by a mechanical force on a suitable material and changes the relative permeability, or C is caused by introducing a suitable gas or liquid into the electromagnetic field of at least one coil (L1), or D these coils (L1, L2) the coils ( 2.1 . 2.2 ) in the arrangements of claims 1 to 5.