Inductive sensor arrangement and measuring arrangement for its use.

The invention relates to an inductive sensor arrangement according to the preamble of claim 1 and a measuring arrangement according to the preamble of claim. 13

Sensor arrangements for determining the relative position of the tools with respect to a workpiece to be machined are known in particular as the height controllers capacitive or inductive type for a long time and in use. Such sensor arrays are for example in the DE-OS 27 26 648, describes 27 47 539 and 28 29 851st

In inductive devices in usually on the tool, a coil is provided, which is likewise designed as a frequency-determining or frequency-determining element of a resonant circuit, being caused by the change in distance between the coil and workpiece, a different attenuation and inductance of the coil and thus of the resonant circuit.

Such sensor arrangements are suitable only for measuring the distance on flat objects and are, for example, not usable when it comes near object edges or at irregular objects or in the case of objects with slots or other interruptions without interference by such irregularities to determine the distance constant or even to the irregularities, such as the columns to follow. As will be evident namely, by such an irregularity, such as a column affects the inductance and the capacitance in the same way as it would be the case if the coil or the capacitor plate further away from the workpiece. Thus, the signals can be no differentiation between too great a distance and an irregularity in the surface, such as a column or an edge to.

EP-A-0016638 shows a passive inductive measuring probe for measuring the distance to a plurality of coils, which are fed by alternating current. Each of the coils has to two external terminals.

For all coils so is "transmitter coil" in the terminology of the present invention. The current through this transmitter coils is measured, impedance changes of the "transmitter coil" themselves are determined by Wirkelstrom-repercussions. Such distance measuring devices sing in many known and conventional, as well as from the German Offenlegungsschrift 2,747,538, which goes back to the same inventors as the present application. Such distance measuring devices are not suitable for determining the position of objects with an irregular surface, for example on workpieces with longitudinal grooves, bores, welds and the like. At most, can be manufactured in the same distance to different walls of a housing -Provided, the electrode diameter is smaller than the opening of the housing.

So 638 three is clear just from EP-A-16:<ul><li>1. The introduction of the known probe in a hole requires that the hole is greater than the probe - smaller holes are position moderately undetectable;</li><li>2. Bigger holes, or hole edges can not be detected in position comparatively well, because the coverage of the coil is limited by the extension of the magnetic field and the sensitivity of the measuring system; </li><li>3. The arrangement can only be used for the middle-determination of holes (with the above restrictions), not for any other purpose, such as seam detection or investigation of property surveys. With a sensor assembly according to the invention, the stated in EP-A-16 638 task would much easier, faster and, above all, with greater sensitivity, ie solve accuracy.</li></ul>

The citation documented as technical background, the state of the art in 1980 (the filing date of the citation) and clearly demonstrates the inventive performance of the application object.

The DE-A-2928899 shows an apparatus for Bestimmnen the center of a weld seam. Here, a magnetic field is generated in an iron pipe by separately arranged coils. Magnetic stray fields are determined by magnetic flux measurement arrangements.

The arrangement is suitable only for Evidently magnetic materials - the generation of a magnetic flux is a prerequisite! (With the sensor according to the present invention, all electrically conductive materials can be detected.) In addition, the arrangement in a practical Anewendungsbereich dramatically constricting manner susceptible: in many machining operations is in the object to be processed induced external noise voltage - as with all electrical welding processes, the eroding etc. It also can change the electrical conductivity of the material, which inevitably leads to measurement errors also be in machining operations.

The different operation of the DE-A-29 28 899, in particular also from the fact clear that the voltage induced in the search coil voltages are in phase, and generally have the same amplitude. Only the noise spikes are not equal - a consequence of Schweillnaht. The sine curve of the basic magnetization is even filtered out in the evaluation.

The GB-A-2,085,594, US-PS 4,015,101 and US-PS-3, 171, 071 documenting the prior art discussed above.

The object of the invention is therefore to improve the known measurement and sensor systems, in particular with the simplest, economical design genaurere signals to obtain and also in the case of irregularities, in particular column in the object (or between two objects) usable and in particular differentiated measurement to ensure signals.

According to the invention, this is achieved according to characterizing by arrangements part of claim 1 or claim. 13

In the invention, therefore, a direct inductive coupling of the receiver coil and the transmitter coil is provided - is influenced by the object the original generated by the transmitter coil electromagnetic field that also covers the unmittelbasr and inductive-coupled receiver coils and the object. Interference voltages accordingly act regularly on the total field, they have a uniform in two receiver coils and are therefore automatically compensated.

In the sensor assembly of the present invention passes through Objektunregelmässigkeiten a phase shift of the currents in the partial windings, which also allows an evaluation of how amplitude fluctuations in the output circuit of the receiver coils. Thus, the invention allows a direct measurement acquisition in the generated electromagnetic field, especially with the advantages of greater accuracy, lower susceptibility to interference, yet simplified design.

The invention is thus ity departed from the known principle of influencing a frequency-determining inductance or capaci and instead generated by a transmitter coil an alternating field, which induces an alternating voltage in the partial windings of the receiver coil. Through the object, for example the metal workpiece is changed the alternating field at the approach. Accordingly, the induction of the transmitter coil being directly affected in the receiver coil. The fact that the two partial windings be removed at a change in position of the object different from the object or approaching this, there is a different field distribution of the RF field and a phase shift in the two sub-windings. By comparing the partial voltages of the two partial windings can thereby determine the simplest way the stock change of the object. Most simply, this can be done by the partial windings directly ( "direct") are connected together with opposite winding senses, so cancel the partial voltages of the partial windings, provided they are equally influenced by the object. Changes, however, the relative position of the object, then occurs a different influence of the two sub-windings and the partial voltages compensate only partially, so that the receiver coil emits a usable signal. Since a change of the field distribution of the rf fields and also an inductance change caused by the object, resulting from the change in position of a different inductance of the two windings, so that a phase change of the AC voltage at the output of the receiver coil compared with the signal of the transmitter coil can be determined , This phase change is substantially better than a voltage change for evaluation in many cases. Evidently can therefore be divided into two partial windings, both the sender and the receiver coil. In the subdivision of the receiver coil, however, particularly high sensitivity of the arrangement can be achieved.

The sensor arrangement is particularly sensitive to changes in the relative position when the receiver coil disposed on the object side facing the transmitter coil and / or is directed to the winding axis toward the object. Characterized namely primarily occurs a phase shift in the partial windings of the receiver coil, which is usable for the Ausfgangssignal, and not acting on both receiver coils attenuation of the field of the transmitter coil.

The phase changes in the signals of the receiver coil described above are also very particularly pronounced detectable, even though the transmitter coil has at least two oppositely wound partial coils, with the two turns of each double winding or at a different distance from the receiver coil the partial windings of the receiver coil are arranged. The two turns of the double coils generate namely respectively an opposing alternating field which is provided the same distance from the coils, cancels. Due to the different spacing of the partial windings of the receiver coil, however, no complete field compensation. In the two part windings of fields of different phase angle due to the different distances of the two turns are induced. Therefore, when one of the two sub-windings strongly attenuated and additionally changed in the inductor, so this results in a preponderance of the voltage and phase of the other sub-windings, creating a strong and well measurable change in phase at the output of the receiver coil winding portions can be determined.

Instead of a so to speak, direct compensation of the two part windings of the receiver coil by countercurrent series connection in the reverse winding direction can of course also each of the coils separately to an evaluation circuit, advantageously a differential amplifier are connected, and then the amplified signals may be processed, are thus compared with each other, for example. It then can be used in a known manner at the same time damping through rapprochement and phase shift by a lateral offset with respect to the workpiece Ünregelmässigkeit calculated separately and evaluate.

For scanning Objektunregelmässigkeiten such as column, possibly also for the actual measurement of the width of such columns or other Objektunregelmässigkeiten it has proven bosonders if the partial windings are arranged perpendicular to the object on both sides of Objektunregelmässigkeit. The partial windings can be arranged from the object and from the transmitter coil but also horizontally juxtaposed and forming a gap between them at the same distance.

If the relative position of the receiver coil to a point-like object, as well as a hole in the object to be detected, an even plurality may be provided by sub-windings that are in pairs, connected together. In this way can be determined by appropriate comparison changes in position of the object in virtually any direction. Particularly advantageous lässte achieve this, when the partial windings of the receiver coil are formed in the cross section approximately of a circular segment.

Particularly advantageously, the invention can be realized when the partial windings of the receiver coil are arranged symmetrically to the transmitter coil. DBEI it can be either point-symmetrical and axially symmetrical arrangement. For axially symmetric arrangement can be achieved that the receiver coils as long hand it in at the opposite circuit and same number of turns, no signal, as the metallic object, in particular the workpiece affects both partial windings in the same way. This can be for example in a completely new way by evaluating that the sensor assembly is symmetrically disposed about a gap in the workpiece, as is apparent, for example the welding of steel plates. As long as the sensor assembly is guided precisely centrally above the gap, both partial windings are affected in the same way and it is - completely independent of the height above the gap - lein signal appearing at the output of Emfpängerspulen. Modified By contrast, the position of the sensor assembly side, then one of the two Emfpängerspulen are influenced more by the workpiece, it occurs in inductance and appears the deviations characterizing signal at the output of the receiver coil.

In contrast, if the approach of the receiver coil on the side of a Objektunregelmässigkeit, such as an object edge, be determined, it may be emphehlen, the receiver coils approximately parallel to the object, so that "lying" and the transmitter coil either on the opposite the object side of both partial windings or to arrange between the two sub-windings. Characterized in that the two winding elements have a different distance to the object, each of the inductance of the two partial windings is affected differently by changing the relative position of the object, which leads to different phase shifts and attenuations.

By placing the additional auxiliary sensors, the distance of each of the partial windings determine the object. If different distances and different influence of the coil, ie an asymmetrical superimposition of caused by the Objektunregelmässigkeiten interference is detected, can be reached compensation of eventually caused the error.

The invention is described below in exemplary embodiments with reference to the drawings. Show it:<ul><li>Figure 1 is a schematic illustration of an arrangement having the features of the invention in side view,</li><li>Figure 1a, the sensor arrangement according to Figure 1 with two auxiliary sensors,</li><li>Figure 2 shows the sensor arrangement according to Figure 1 from below</li><li>Figure 2a shows the sensor arrangement according to Figure 1a from below</li><li>3 shows a modified embodiment of the invention</li><li>Figure 4 shows a further modified embodiment, in which the receiver coil consists of four partial windings consists,</li><li>Figure 5 shows the block diagram of an evaluation circuit with a sensor arrangement,</li><li>Figure 6 shows a sensor assembly with indirectly connected to the partial windings</li></ul>

According to Figure 1 is one of two partial windings (a, b) existing transmitter coil 1 is disposed on a ceramic-coil carrier 2 and connected to a high frequency oscillator third By opposing winding arrangement of the coil elements a, b transmitter coil 1 no high-frequency noise emitted by this because each opposing fields of the reverse turn portions a and b compensated. However, the spacing of the coil sections A with respect to the sub-windings 4a and 4b, a receiver coil 4 is greater than the distance of the winding sections b of the transmitting coil 1. This outweighs 4a with respect to the induction in the partial windings and 4b of the field of the coils b, so that in the partial windings an alternating voltage is induced 4a and 4b.

As is also evident from Figure 2, however, the partial windings 4a and 4b are in turn wound in opposite directions and have the same number of turns, so that compensate for the partial voltages in the partial windings 4a nd 4b and at the entrance 5 of an amplifier 6 with no input signal, as long as the partial windings 4a and 4b are not disturbed in their existing Symemetrie. Among the sub-windings 4a and 4b an object 7 is symmetrically aligned with illustrated schematically the overall arrangement. In the illustration, the object 7 is also perfectly symmetrical with respect to the partial windings 4a and 4b, so that the metallic object 7 outgoing Induktivitätsbeeinflussung in both partial windings 4a and 4b has the same effect and the signal is compensated accordingly-law prevalent at the outlet. However, changing the relative position of the object 7 in dashed manner indicated, the winding is Evidently 4a influenced significantly stronger, resulting in a change in the inductance and the phasing in of the partial winding 4a result. Accordingly, the partial voltage in the partial winding 4a no longer corresponds to the portion of voltage in the partial winding 4b, the change affects both the voltage value and the phase position. accordingly appears a signal which corresponds to the amplitude and the phase position of the change in the relative position of the object in the dotted line position at the entrance 5 of the amplifier. 6 The evaluation of this signal, for example. for triggering a warning signal or for evaluation and presentation of a corresponding one of the differential signal or to activate a tracking control, is not the subject of this invention and needs no further explanation.

1a and 2a show a sensor according to Figures 1 and 2, in which an auxiliary winding 4c and 4b into the partial winding an auxiliary winding 4d are introduced into the partial winding 4a.

Both auxiliary windings are provided with two coils I and II, which are arranged in succession staggered in depth in Figure 2a. This gives Figure 1a closer to (side view). The bobbin 2 of the main sensor is shown in dashed lines. The auxiliary winding 4c consists of two coils 1 and II, which are mutually connected so that cancel when properly adjusted to the transmitting coil 1, the voltages in legs partial coils. occurs at the output of the amplifier 5a to no voltage.

Similarly, the two coils are in the right auxiliary winding 4d of the main sensor I and II provided on the bobbin support 1 and also so adjusted that in the normal state, the two coils cancel each other and also in the output of the amplifier 6a no voltage occurs. The amplifier 5a and 6a of the amplifier are connected to the reference input to the RF oscillator third They may by signals that differ in phase from the original signal of the RF oscillator to be converted into a positive or negative DC voltage.

A tilted leigendem workpiece 9 (Fig. 1a) is the auxiliary winding 4d 4c influenced more than the auxiliary winding. On the other hand it is not so much dependent side affects such as the partial winding 4b in the right part of the main sensor, because it lies further towards the center. The object of the auxiliary winding 4d is in this case to produce a Korrrektursignal which can be compared with the signal generated by the auxiliary winding 4c. This is realized in that the voltages from the amplifiers 5a and 6a supplied to a differential amplifier 10 which outputs a difference signal in dependence on the oblique position of the workpiece. This difference signal is then used to compensate for the error of the main signal from the sub-windings 4a and 4b of the sensor.

In the following embodiments, partly no auxiliary sensors are shown to constitute the basic function of the device easier. Each -Ausführungsbeispiele shown can of course be formed with or without auxiliary sensors.

Figure 3 shows a modified embodiment in which the two sub-windings 4a and 4b are arranged on both sides of the transmitter coil first The partial windings 4a and 4b are wound in opposite directions as in the embodiment according to Figure 1 and up to today ges lever was. As long as the receiver coils 4a and 4b are located in the manner shown, exactly symmetrical across a gap 7a of the object 7, so the partial voltages of the two partial windings 4a and 4b are compensated for and at the entrance 5 of the amplifier 6 is in this case no signal. However, once the relative position of the part-windings 4a, 4b laterally displaces the gap 7a, which is closer to the gap 7a executed long end or reaching across the gap 7 a partial winding due to the existing gap is less affected by the object 7 than the other part winding. Accordingly, the balanced, symmetrical state of the two part-windings 4a and 4b and disturbed at the output of the receiver coil 5 or at the input of the amplifier 6 enters the corresponding deviation signal which can be further processed in a suitable manner.

Figure 4 shows a modified embodiment of an arrangement according to FIG 1. In this case, four partial windings are provided 4a and 4d crosswise against each other. As long as an object is located right in the middle among the four sub-windings 4a through 4d, the system is balanced and it seems no suspense. However, there is an unbalance, that is, the relative position of the object changes with respect to the four sub-windings 4a to 4d, are present at the inputs 5a and 5b of the amplifiers 6a and 6b of the deviation proportional input signals from which the direction of the deviation as well as the can determine its degree.

Figure 5 shows schematically an evaluation circuit which can be connected to one of the sensor arrangements described above. The part-windings 4a and 4b also schematically shown are connected to the input 5 of amplifier 6, whose output is connected to a phase comparator 9a. The phase comparator 9d is also fed directly from the RF oscillator 3, which is also connected to the transmitter coil. Once the 4a and 4b made of the transmitter coil 1 and the partial windings sensor arrangement according to FIG 5 also moves in direction of the arrow on the edge of an object, occurs such inductance that the phase of the signal at the input 5 of the amplifier 6 as compared to the phase of the RF -Oszillators 3 changed greatly. This phase shift is detected in the phase comparator 9 and leave at the exit 10 as an analog signal. This signal can be in a suitable manner, for example, for issuing a warning signal or the like, for further processing.

Figure 6 schematically illustrates an alternative embodiment in which the two sub-windings 4a and 4b are connected to two amplifiers 6a and 6b and are not placed directly against each other. On the output side, the two amplifiers 6a and 6b are connected to the input of a comparator. The operation of the device is comparable with the operation of the arrangement according to FIG 1 to 4. For as long as 4a and 4b emit two partial windings due to the given symmetry sensor arrangement identical signals with different polarity, no output occurs at comparator 11th However, for example, changed by approach of an object, one of the part-windings 4a or 4b in the inductance, the input signal is changed to one of the inputs of the comparator 11 and there is an output signal. Of course, other ways of indirect negative feedback or counter circuit and the comparison of the output signals of the two sub-windings 4a and 4b are also conceivable.