WO2014191352A2

WO2014191352A2 - Inductive sensor

Info

Publication number: WO2014191352A2
Application number: PCT/EP2014/060829
Authority: WO
Inventors: Ralf Ph. SCHMIDT
Original assignee: iCONTROLS k.s.
Priority date: 2013-05-27
Filing date: 2014-05-26
Publication date: 2014-12-04
Also published as: DE102013209805A1; WO2014191352A3

Abstract

In order to detect a material and/or shape parameter of a metal object (3), an inductive sensor (1) is proposed, the transmission coil (5) of which, said transmission coil being excited by rectangular drive pulses, induces eddy currents in the metal object (3), and the secondary magnetic field of the eddy currents are detected by a magnetic field sensor (9). The response signal of the magnetic field sensor (9) is analyzed exclusively over the duration of the rectangular drive pulses exciting the transmission coil (5). Advantageously, the transmission coil (5) and the magnetic field sensor (9) have main magnetic field axes (7, 11) which are inclined towards each other in the direction of the metal object (3).

Description

Inductive sensor

description

The invention relates to an inductive sensor for detecting a material and / or shape parameter of a metal object.

Time-varying magnetic fields induce eddy currents in metal objects, whose secondary magnetic field of material and / or

Depending on the shape parameters of the metal object, which is flooded by the time-varying primary magnetic field of a transmitting coil. A responsive to the secondary magnetic field magnetic field sensor provides a response signal which information about the material and / or

Contains shape parameter of the metal object or represents this information and allows conclusions about the material and / or shape parameters.

From US 2003/0193331 A1 it is known for material monitoring coated gas turbine blades cracking, by means of a through

Rectangular pulses excited the transmitter coil in the blade to induce eddy currents whose secondary magnetic field is detected by a magnetic field sensor, such as a Hall sensor. The magnetic field sensor is arranged coaxially in the transmitting coil supplying the primary magnetic field. An electrical evaluation circuit compares the response signal delivered by the magnetic field sensor in a test position with a reference signal which represents the material and / or shape parameter in a reference position of the blade. The evaluation circuit thus provides an information signal which, based on the reference position, represents a measure of any cracks present in the test position. The evaluation circuit monitors with respect to the primary

Magnetic field in the transmitting coil generating drive pulse, the amplitude of the response signal generated by the magnetic field sensor or the time a zero value of the response signal.

From DE 10 20 0 009 923 A1 an eddy current sensor is known, which allows the determination of the thickness of a metal plate. The eddy current sensor comprises an AC-fed transmitting coil and a spaced-apart thereof, connected to an evaluation circuit

Receiving coil, wherein the metal plate for the measurement of its thickness between the transmitting coil and the receiving coil is arranged. To the

Coupling the transmitting coil and the receiving coil through the metal plate to each other, both the transmitting coil and the

Receiver coil U-shaped cores made of ferromagnetic material

assigned, whose legs are directed towards each other.

From EP 2 312 338 A1, it is known for the detection of electrically conductive objects to arrange equiaxially axially on both sides of a transmitting coil two receiving coils connected to a differential coil arrangement. The transmitter coil is driven by driving pulses of a

Pulse generator energized while the differential coil assembly is connected to an evaluation circuit that analyzes the waveform of the response signal of the receiving coil and depending on the times at which maximum values, minimum values, zero values or inflection points of the waveform occur detects the electrically conductive object.

In known, based on the eddy current inductive

Sensors, the deviations of the response signals in the test positions of the response signals of the reference positions are often low, which reduces the accuracy with which material and / or shape parameters can be detected, decreases. In addition, it has been shown that in conventional inductive sensors of this type, the distance of the transmitting coil and / or the magnetic field sensor from the metal object to be tested has a comparatively large influence on the determination of the material and / or shape parameter, which on the one hand, the accuracy of the determination deterioration of the material and / or shape parameter, or the built-in Limited situation when the inductive sensor is part of a plant or a machine with predetermined installation space ratios.

Finally, it has been found that conventional inductive sensors of the type described above are not or only insufficiently applicable in a large number of applications, in particular when it comes to the rapid and reliable detection of material and / or shape parameters in an in-line inspection or processing of metal objects , Examples of this are the recognition of a gap between two metal parts or the

Material change by welds or welds also for the positioning of the metal objects in a suitable for subsequent processing spatial location. Other examples are the detection of screw nuts, which are concealed behind holes in sheet metal parts or the detection of undesirable adhering sheet metal parts in a designed for feeding of sheet metal parts manufacturing plant. Another field of application in which conventional eddy-current sensors can only be used to a limited extent is material recognition, for example the distinction between

Non-ferrous metal parts, iron parts or parts made of stainless steel. Conventional eddy current sensors are also only limited for the determination of hardness differences, in particular the surface hardness of

Metal objects.

It is an object of the invention, according to the eddy current principle

specify working inductive sensor, which allows to determine a material and / or shape parameters of a metal object more precise than before.

The invention is based on an inductive sensor for detecting a material and / or shape parameter of a metal object, which comprises:

a pulse generator,

at least one excitable by driving pulses of the pulse generator Transmitting coil for inducing eddy currents in the metal object,

at least one responsive to magnetic fields of the eddy currents induced in the metal article and one of the

Eddy current dependent response signal supplying magnetic field sensor, in particular in the form of a Empfangsspuie and

an evaluation circuit which responds to the response signal and which represents a material and / or shape parameter

Information signal provides.

In a first aspect of the invention it is provided that the

Transmitter coil and the magnetic field sensor are arranged transversely to their magnetic main axes side by side and the metal object based on the magnetic field main axes on the same side of the transmitting coil and the magnetic field sensor can be arranged, wherein the

Transmit coil and the magnetic field sensor towards the metal object

have mutually inclined magnetic main axes.

In this way it is achieved that the center of maximum sensitivity of the receiving coil at least overlaps, if not substantially completely covers, the region of maximum eddy currents induced by the transmitting coil in the metal object. This increases the

Sensitivity of the response signals and thus the accuracy with which the material and / or shape parameter of the metal object can be detected.

The sensitivity of the sensor can be improved in particular if, as will be explained in more detail below, the transmitting coil and / or the magnetic field sensor are associated with magnetic shielding means which prevent the magnetic field sensor from directly exceeding the magnetic field

At least partially shield the transmitting coil. As will be explained in more detail below, the shielding means may be a shielding wall arranged between the transmitting coil and the magnetic field sensor act. Additionally or alternatively, the transmitting coil and / or the magnetic field sensor can be shielded individually.

In a second aspect of the invention, the improvement consists in that the transmitting coil and the magnetic field sensor are arranged side by side, either

the transmitter coil and the magnetic field sensor in the direction of their

Magnetic field main axes are arranged opposite each other at a distance and the metal object between the transmitting coil and the magnetic field sensor is inserted or

the transmitting coil and the magnetic field sensor are arranged side by side transversely to their magnetic field main axes and the

Metal object related to the magnetic field main axes on the same side of the transmitting coil and the magnetic field sensor can be arranged and that the evaluation circuit responds to the first occurring during the drive pulse in the waveform of the response signal extreme value and / or zero value and / or inflection point value and / or at least one However, a predetermined time after the start of the drive pulse still occurring during the drive pulse amplitude value of the waveform of the response signal responds and that the material and / or shape parameters

representing information signal depending on the amplitude of the extreme value and / or the amplitude value occurring at the predetermined time and / or depending on the time interval of the extreme value and / or the zero value from the beginning of the drive pulse and / or the waveform slope of the inflection point value.

In such an inductive sensor, the information signal representing the material and / or shape parameter is already determined during the drive pulse, ie within a time span in which the drive pulse excites the transmit coil. It has been found that the response signal of the magnetic field sensor when the transmitting coil is excited is less susceptible to interference than in the case of an evaluation of the response. Signals with decaying excitation after the end of the drive pulse, as is common practice in conventional inductive sensors of the type in question. The drive pulses are preferably narrow rectangular pulses with a pulse width between about 10 ns and 10 ps. The drive pulses are expediently generated periodically with a pulse break which is sufficiently large to ensure that the influence of the drive pulse on the response signal has decayed to a negligible value until the occurrence of the next drive pulse. Conveniently, the pulse interval is on the order of 50 to 200 ps. In this way, each by individual

Driver pulses specific response signal contains a wide

Frequency spectrum, which allows to determine even relatively small changes in the material and / or shape parameter with sufficient accuracy.

The inductance of the transmitting coil and the amplitude of the driving pulse are dimensioned such that the response signal already has an extreme value during the pulse duration of the driving pulse. In a driving pulse starting with a rising edge, the extreme value is a maximum value of the response signal. For a drive pulse beginning with a falling edge, the response signal starts at a minimum. The extreme value is followed by a zero value of the response signal. The transmitter coil is expediently dimensioned such that the zero value also occurs during the pulse duration of the driver pulse; However, the zero value may also depend on the inductance of the transmitting coil, the amplitude of the

Driver pulse and the material to be determined and / or shape parameter of the metal article after completion preferably shortly after

Termination of the drive pulse occur. It has been found that the signal edge of the response signal leading from the first extreme value to the first zero value of the response signal is also a measure of the material and / or shape parameter of the metal object to be determined. The determination of the material and / or shape parameter representing

Information signal according to the invention is dependent on the occurring during the drive pulse first extreme value and / or the first Zero value in the signal response of the response signal and / or dependent on an occurring during the drive pulse region of the signal edge of the response signal between the first extreme value and the first zero value and / or at least one inflection point value of the waveform. For the information signal, the time of the first extreme value and / or the time of the first zero value in each case based on the beginning of the driver pulse can be evaluated here. Additionally or alternatively, however, the amplitude value of the first extreme value and / or the amplitude value of the signal edge between the first extreme value and the first zero value and / or the signal progression gradient determined at a predetermined time during the drive pulse at the inflection point value for the determination of the material and / or form parameter representing information signal to be evaluated.

It has been shown that the evaluation of the extreme value, the zero value, the inflection point value or the signal edge can be carried out with comparatively little circuit complexity, without the accuracy of determining the material and / or shape parameter suffering. It is understood that in individual cases, the evaluation of a single of the above values is sufficient. However, the accuracy can be increased if more than one of these values is taken into account. Furthermore, it has been shown that the above-explained type of determination of the information signal usually little of the position of the

Metal object relative to the transmitting coil or the magnetic field sensor depends. The distance of the metal object from the transmitter coil or the magnetic field sensor can therefore vary without this having any effect on the information signal.

An evaluation circuit of the type explained in the second aspect of the invention is preferably also used in the first aspect of the invention. However, the signal profile of the response signal of the magnetic field sensor can also be achieved by correlating the signal profile of the response signal with a reference signal profile or else Information signal is transmitted by methods of a fast

Fourier transformation analysis (Fast Fourier Transformation).

The inductive sensor according to the invention is particularly suitable for determining deviations of the material and / or shape parameters of the metal object from a reference value of the parameter, as can be determined for example in a reference position of the metal object by means of the same inductive sensor. It is understood, however, that the reference value can also be predetermined based on empirical values.

In conventional, operating on the eddy current inductive sensors, the magnetic field sensor with the primary magnetic field generated by the transmitting coil is usually firmly coupled. In the context of the invention, it has been found that in the above-described evaluation of the response signal by determining extreme values, zero values and signal edge values, the accuracy of the evaluation can be improved if the direct magnetic field coupling of the transmitting coil and of the magnetic field sensor is reduced. In a first alternative of the

The inductive sensor according to the invention, the transmitting coil and the magnetic field sensor are arranged on opposite sides of the metal object at a distance from each other, wherein the magnetic field sensor responsive to the secondary magnetic field induced by the primary magnetic field of the transmitting coil in the metal object eddy currents. Of the

Metal object is expediently chosen in its dimensions so large that it also acts for eddy current shielding of the primary magnetic field with respect to the magnetic field sensor. The

Transmitting coil and the magnetic field sensor are in this case in the direction of their magnetic field main axes opposite each other, in particular coaxially with each other, so that the magnetic field sensor is substantially aligned with the range of maximum eddy currents. Under one

Magnetic field main axis is to be preceded and understood in the following the axis, along which the transmitter coil their magnetic field strength maximum has, or the magnetic field sensor its largest

Magnetic field strength sensitivity has.

In an alternative of the inductive sensor according to the invention, however, the transmitting coil and the magnetic field sensor are arranged at a distance from each other on the same side of the metal object, transversely to their magnetic field main axes. In this way, the proportion of the magnetic fields that cross over from the transmitting coil directly onto the magnetic field sensor can be reduced, with which the relative influence of the eddy currents induced in the metal object on the response signal increases. According to the first aspect of the invention, even in the second aspect, the magnetic field main axes of the transmitting coil and the magnetic field sensor are inclined toward each other toward the metal object, so that, despite the

Transverse distance of the magnetic field sensor from the transmitting coil of the range of maximum field strength sensitivity of the magnetic field sensor with the

Range of maximum of the transmitting coil in the metal object

induced eddy currents can be aligned overlapping.

In a preferred embodiment of the first and second aspects of the invention, the transmitting coil and / or the magnetic field sensor

associated magnetic shielding means which at least partially shield the magnetic field sensor against directly exceeding magnetic field of the transmitting coil. The shielding means may be ferromagnetic material. Preferably, however, it is after the

Eddy current principle working shielding from a not

Ferromagnetic material, since such shielding in the presence of strong foreign magnetic fields, such as may occur in electrical welding systems, for example, show no saturation behavior. The shielding means may be a shielding wall arranged between the transmitting coil and the magnetic field sensor. Additionally or alternatively, the transmitting coil and / or the magnetic field sensor may be arranged in a shield cup open in the direction of the magnetic field main axis. It is understood that the shield cup optionally may have the shape of a socket open on both sides or the like.

In addition to or instead of the passive magnetic shielding means explained above, the magnetic field sensor may have another, through

Driver pulses excitable transmission coil be assigned, the magnetic field directly overflowing magnetic field of the transmitting coil on the magnetic field sensor actively compensates, but at least weakens.

The adjustment of the response signal of the magnetic field sensor relative to the drive pulse can be determined not only by the dimensioning of the

Transmit coil or affect their excitation by driving pulses.

In particular, for the zero-value compensation of the response signal, a compensating sheet metal part can be arranged on the side facing away from the metal object side of the transmitting coil and / or the magnetic field sensor, which changes the waveform of the response signal due to the induced eddy currents in it. By suitable choice of the material, the shape and / or the dimensions of the compensation sheet metal part, in particular, the zero value of the reference response signal can be adjusted to zero.

The response signal of the magnetic field sensor can be influenced by reference materials brought directly into the influence range of the transmission coil and / or the magnetic field sensor, in particular for compensation or adjustment of the reference zero value of the reference response signal. In alternatives, in which the transmitting coil and the magnetic field sensor on opposite sides of the examined

Metal object can be arranged, the comparison of the

Realize the response signal with the reference signal associated with a reference in a two-channel system. This can be done on the

Magnetic field sensor side facing away from the transmitting coil at a distance from the transmitting coil, a further magnetic field sensor, in particular also be arranged in the form of another receiving coil, between the transmitting coil and the further magnetic field sensor, a reference metal object is arranged, in which the transmitting coil eddy currents induced on the magnetic field of the further magnetic field sensor responds, wherein the evaluation circuit for forming the reference value

Response signals of the further magnetic field sensor responds. Alternatively, it can also be provided that on the side remote from the transmitting coil side of the magnetic field sensor another by driving pulses of the

Pulse generator excitable transmission coil at a distance from the

Be arranged magnetic field sensor. Between the magnetic field sensor and the further transmitting coil, a reference metal object may be arranged, in which the further transmitting coil induces eddy currents, on the magnetic field of which the magnetic field sensor also responds, wherein the

Evaluation circuit provides the information signal depending on the difference of the response signals of the transmitting coil and the reference value.

A further transmitting coil or a further magnetic field sensor can be dispensed with if a reference metal object is additionally arranged between the transmitting coil and the magnetic field sensor in which the magnetic field of the eddy currents induced in the metal object to be investigated induces secondary eddy currents, to which the magnetic field sensor then responds or in which the magnetic field of the transmitting coil induces eddy currents whose magnetic field in turn induces the secondary eddy currents in the metal object to whose magnetic field the magnetic field sensor responds.

In a preferred embodiment, the transmitting coil and, as far as the magnetic field sensor is designed as a receiving coil, and the

Reception coil designed as air coils. In contrast to coils with a ferromagnetic core, such as a ferrite core, inductive sensors with air coils are not affected by magnetic foreign fields, since air coils show no saturation behavior. In this way, for example, welding resistance of the inductive sensors can be achieved.

The amplitude of the evaluated during the drive pulse The response signal of the magnetic field sensor can fluctuate greatly, in particular if both extreme values and zero values are used for the evaluation

should be taken into account. In a preferred embodiment, therefore, the evaluation circuit has an amplifier with a non-linearly decreasing gain factor as the input signal amplitude increases. For example, a logarithmic amplifier is suitable.

In the following the invention will be explained in more detail with reference to a drawing. Hereby shows:

Figure 1 is a schematic representation of a first embodiment of an inventive, operating on the eddy current principle, inductive sensor;

Figures 2a and b are timing diagrams of a transmission coil of the sensor supplied driving pulses or detected by means of a receiving coil response signals;

Figure 3 is a schematic representation of a second embodiment of an operating according to the eddy current principle inductive sensor;

FIGS. 4 to 6 variants of the inductive sensor according to FIG. 3.

Figure 1 shows an operating according to the eddy current principle, inductive sensor 1, with a material and / or shape parameter of a

Metal article 3, for example, a sheet metal part or a cast molding or the like and / or the deviation of this parameter can be detected by a reference value. The sensor 1 has a transmitting coil 5, designed as an air coil, whose magnetic field main axis 7 is directed onto the metal object 3. On the same side of the

Metal object is at a distance next to the transmitting coil 5 a

Magnetic field sensor 9 here in the form of an air-core coil Reception coil arranged whose magnetic main axis 11 is directed at an angle α against the magnetic field main axis 7 of the transmitting coil 5 inclined to the metal object 3. The magnetic field main axes 7, 1 1 thus have a smaller distance on the metal object 3 than between the transmitting coil 5 and the magnetic field sensor 9.

The transmitting coil 5 is excited by a series of rectangular pulses 13 (FIG. 2a) of a pulse generator 15, thus generating a primary one

Magnetic field in the metal object 3 in a region 17th

Eddy currents induced on the secondary magnetic field of the

Magnetic field sensor 9 responds. Since the magnetic field main axes 7, 1 1 are inclined towards each other toward the metal object 3, the maximum sensitivity range of the magnetic field sensor 9 overlaps the range of maximum eddy currents induced by the transmitting coil 5, which is the

Sensitivity of the sensor benefits.

The magnetic field sensor 9 is connected to an evaluation circuit 19 which receives a response signal S (FIG. 2 b) dependent on the secondary magnetic field via an amplifier 21 and evaluates it in more detail below with reference to FIGS. 2 a and 2 b and with one in a memory 23 stored reference value. The evaluation circuit 19 outputs the material and / or shape parameter or its deviation from a reference value

Information signal at an information output 25 from. It is understood that the evaluation circuit 19 instead of the response signals also

Can compare information signals with each other.

The reference value in the memory 23, which may be a group of values indicative of the reference, may be given empirically or, as shown in Figure 1 for the region 17, measured in a reference position of the metal object 3 and

get saved. If the sensor 1 is directed to areas of the metal object 3 with a different configuration, the evaluation circuit supplies 19 an information signal deviating from the reference value, which represents the change of the material and / or shape parameter of the metal object 3. At 17 'is an example behind a hole 27 on the sensor 1 facing away from the back of the metal sheet article 3 consisting of sheet metal, for example, is welded and thus is not perfectly recognizable from the front of the metal object 3. The sensor 1 compares the response signal evaluated for the area 17 'with the reference response signal evaluated for the reference area 17, which allows a proper identification as to whether the nut 29 is present or not. At 17 ", as another example, a weld 31 is attached to the sheet metal article whose position relative to the metal object 3 is identifiable when the sensor 1 and the

Metal object 3 are moved relative to each other. The sensor 1 thus allows automated alignment of the metal object 3 for further processing. The sensor 1 also permits detection of other parameters, for example the detection of degrees of hardness, in particular surface hardness grades of metal components and their deviation from a reference value. Furthermore, metal objects can be classified according to the type of metal, such as non-ferrous metal, steel or stainless steel.

As shown in FIG. 2a, the transmission coil 5 is excited by a sequence of rectangular drive pulses 13 of constant amplitude P ₀ . The drive pulses 13 have a pulse width T ₀ between a few nanoseconds and a few microseconds, preferably about 2 to 3 ps. The drive pulses 13 are separated from each other by pulse gaps Ti, which is substantially longer than the pulse width T ₀ and, for example, between 50 and 200 ps.

The evaluation circuit 19 examines response signals of the magnetic field sensor 9 essentially only during the pulse duration T _{0 of} the drive pulses, the information signal representing the material and / or shape parameter of the metal object 3 in each case being dependent exclusively on Waveform of the response signal during the duration of the drive pulse 13 is determined. It has been found that the response signal is less affected by foreign influences, as long as the transmitting coil is excited by the driving pulse. Due to the pulse interval Ti, which is considerably longer than the pulse duration T ₀ , the response signal can be up to

The beginning of the next drive pulse decays sufficiently. Because the

Driver pulses are relatively short square pulses, the response signal is influenced by a comparatively large frequency spectrum of the eddy currents, which the accuracy with which material and / or shape parameters of the metal object 3 can be recognized benefits.

FIG. 2b shows by way of example the signal curve of the response signal S of the magnetic field sensor 9 as a function of the time t. With a

solid line 31 is an example of the waveform of the

Response signal of the magnetic field sensor 9 for eddy currents in one

Reference region of the metal object 3 similar to the reference region 17 shown in Figure 1. With the beginning of the drive pulse 13 at the time t ₀ , the signal curve 31 of the response signal increases up to a maximum 33 at the time t _m with the amplitude S _m . After the drive pulse 13 has a constant amplitude P ₀ , the signal curve 31 drops in a falling edge 35 corresponding to the decreasing eddy currents to a zero value 37 at the time t _n . In the present case, the zero value is still reached during the drive pulse before the signal profile 31 drops to a minimum value 39 during the pulse interval in accordance with the falling trailing edge of the drive pulse.

Depending on the material and / or shape parameters of the metal object 3, the signal curve of the response signal of the magnetic field sensor 9 changes, as illustrated by a dot-dashed signal profile 31 'for a material and / or shape configuration of the metal object 3 deviating from the reference region 17. As FIG. 2b shows, the maximum value 33 can change into the maximum value 33 ', wherein not only the time of the maximum value with respect to the beginning t _{0 of} the drive pulse can change from t _m to but also the amplitude value S _{m of} the maximum value in s _m >. Furthermore, the zero value 37 can change from the time t _n to the zero value 37 'at the time t _n -. In addition, the slope and the shape of the falling edge 35 may change, as indicated at 35 '. The flank shape can also be used to detect the material and / or shape parameter of the

Metal object 3 are evaluated, wherein at a predetermined time during the duration of the drive pulse, the amplitude of the signal waveform 31 and 31 'is detected. In the present example, the amplitude value of the signal curve 31 increases from S _t for the reference value to S _r . It is understood that amplitude values S _t and S _f can also be detected at several times ti.

For the determination of the deviation of the material and / or shape parameter of reference values of the parameters and the monitoring whether predetermined limits of deviation are maintained or exceeded, the evaluation circuit 19 forms difference values, for example the time parameters t _m and t _{m '} and / or t _n and t _rf and / or amplitude difference values S _m and Sm and / or S _t and S _r . The difference values are used with limit values and / or threshold windows for the determination of the material and / or

Compared information signal representing information signal. It is understood that the evaluation circuit 19 also evaluate the values of the response signal and / or according to predetermined algorithms for determining the information signal by comparison with limit values and / or

Evaluate threshold windows. Also, differential values of a current information signal and a reference information signal can be formed and compared with limit values and / or threshold value windows.

The waveform of the response signal of the magnetic field sensor 9 may also contain inflection points in the mathematical sense, at which changes the sign of the slope change of the waveform, ie the second time derivative of the waveform is zero. Even such

Turning point values can be evaluated for determining the information signal, for example by comparing the slope value at the inflection point with a reference value or a threshold value and / or threshold value window.

Possibly directly with the magnetic field sensor 9 coupled primary

Magnetic fields of the transmitting coil 5 can influence the response signal of the magnetic field sensor 9 which represents the secondary magnetic fields of the eddy currents. In order to minimize this influence, the magnetic field sensor 9 is not only arranged transversely to the magnetic field main axes 5, 1 1 at a distance from the transmitting coil 5, but between the magnetic field sensor 9 and the transmitting coil 5 is a shielding wall 41 shielding the magnetic field (FIG ) arranged. Additionally or alternatively, the transmitting coil and / or the magnetic field sensor 9 may be arranged in a magnetic field shielding cup 43 which is open to the metal object 3. The shielding wall 41 and the shielding cup 43 may be made of ferromagnetic material, but are preferably formed as eddy current shielding means and made of non-ferromagnetic metal.

The shielding means 41, 43 act passively. Additionally or alternatively, the magnetic field sensor 9, a further from the pulse generator 15 with

Driver pulses excited transmission coil 45 may be assigned to at least partially compensated by the transmission coil 5 directly coupled to the magnetic field sensor 9 magnetic fields. The passive or active shielding measures improve the response accuracy of the sensor to material and / or shape parameters of the metal article 3.

The point in time at which the zero value of the signal curve results depends on a large number of dimensioning parameters of the sensor. In order to compensate for the influence of the dimensioning parameters, the transmitting coil 5 and / or the magnetic field sensor 9 may be assigned the electrically conductive materials influencing the magnetic field, as shown in FIG the metal object 3 facing away from the transmitting coil 5 and the magnetic field sensor 9 is indicated at 47.

In the following, variants of the inductive sensor will be explained.

Equivalent components are denoted by the reference numerals of Figure 1 and provided with a letter to distinguish. To explain the structure and the mode of operation, including possible variants, reference is made to the preceding description of Figures 1, 2a and 2b. The explanations to the figures 2a and 2b apply in full to the embodiments explained below.

Figure 3 shows a variant of an inductive sensor 1 a, which differs from the sensor 1 of Figure 1 only in that the transmitting coil 5a in the direction of their magnetic main axes 7a and 1a are spaced from each other, while the metal object 3a for the determination of the material and / or shape parameter between the

Transmit coil 5a and the magnetic field sensor 9a is located. The transmitting coil 5a and the magnetic field sensor 9a are thus arranged on opposite sides of the metal object 3a. With sufficiently large transverse dimensions of the metal object 3a, as may be the case, for example, in the inspection of metal plates or the like, the metal object 3a simultaneously acts as a shielding of the magnetic field sensor 9a against direct coupling over of the primary magnetic field of the transmitting coil 5a. With the help of such an arrangement can be monitored not only the material and shape parameters, as explained with reference to Figure 1, but for example also separation errors, as may occur in material feeders, if instead, as desired, of individual metal objects, such as Example sheet metal pieces, two or more adhering sheet metal pieces of a further processing

Machine are supplied. It is understood that even with the sensor of Figure 1, a multiple sheet metal detection is possible.

The explained with reference to Figure 1 components 15, 19, 21, 25, 43, 45 and 47 are also present in the sensor of Figure 3. In addition, the magnetic field sensor 9a is expediently designed as a receiving coil, the coils 5a and 9a being air coils.

FIG. 4 shows an inductive sensor similar to the sensor of FIG. 3, but magnetic field sensors 9b and 9b ', which are designed as air coils on both sides in the direction of their magnetic field main axis 7b and excited by rectangular drive pulses, are spaced apart from the magnetic field sensor

Transmitter coil 5b are assigned. The metal object 3b is arranged as shown in FIG. 3 between the transmitting coil 5b and the magnetic field sensor 9b. A metallic reference object 3b is arranged between the transmitting coil 5b and the further magnetic field sensor 9b ', wherein the further magnetic field sensor 9b' detects the secondary magnetic field of the eddy currents induced by the primary magnetic field of the transmitting coil 5b in the reference object 3b '. The not shown

Evaluation circuit is responsive to the difference signal of the response signals of the magnetic field sensors 9b and 9b ', wherein the evaluation of the differential response signal is analogous to the explanations in connection with Figures 2a and 2b. The shielding and compensating means 43 and 47, as explained with reference to FIG. 1 for the magnetic field sensor 9, may be present.

FIG. 5 shows a variant of an inductive sensor that differs from the sensor of FIG. 4 essentially only in that both sides of a common magnetic field sensor 9c, which is embodied as an air coil, have transmitting coils 5c and 5c 'with respect to the magnetic field axes 7c and 1c Distance from the magnetic field sensor 9c are arranged. The metal object 3c is in turn arranged between the magnetic field sensor 9c and the transmitting coil 5c, while a reference metal object 3c 'is provided between the magnetic field sensor 9c and the further transmitting coil 5c'. The two transmitting coils 5c and 5c 'are excited together by driving pulses, as explained with reference to FIG. The response signal of the magnetic field sensor 9c becomes evaluated according to the explanations to Figure 1, 2a and 2b. The shielding means 43 and compensating means 47 explained with reference to FIG. 1 can be present.

FIG. 6 shows a variant of an inductive sensor 1 d, which differs from the sensor 1 a of FIG. 3 essentially in that not only the metal object 3d, whose material and / or material are arranged between the transmission coil 5d and the magnetic field sensor 9d

Form parameter is to be detected, but in addition a reference metal object 3d '. The magnetic field sensor 9d, which in turn preferably takes the form of an air coil, and the transmitting coil 5d are in turn equiaxed but spaced apart from one another with respect to their magnetic field axes 7d and 11d, the reference metal object 3d 'being arranged between the metal object 3d and the magnetic field sensor 9d , In contrast to the sensor 1a of FIG. 3, the magnetic field sensor 9d does not respond to the secondary magnetic field of the eddy currents induced by the primary magnetic field of the transmitting coil 5d in the metal object 3d, but indirectly to a tertiary magnetic field, which in turn is due to eddy currents which are the secondary Magnetic field of the metal object 3d induced in the reference metal object 3d '. It is understood that the reference metal object 3d 'can also be arranged between the transmitting coil 5d and the metal object 3d. The shielding means 43 and compensating means 47 explained with reference to FIG. 1 can be present. The response signal of the magnetic field sensor 9d is evaluated in accordance with the explanations for FIG.

Claims

Expectations

1. Inductive sensor for detecting a material and/or shape parameter of a metal object (3), comprising

a pulse generator (5),

at least one transmitting coil (5) which can be excited by driver pulses (13) from the pulse generator (15) to induce eddy currents in the metal object (3),

at least one magnetic field sensor (9) that responds to magnetic fields of the eddy currents induced in the metal object (3) and delivers a response signal dependent on the eddy currents, in particular in the form of a receiving coil, and an evaluation circuit (19) that responds to the response signal and which is located in the material and/or provides information signal representing shape parameters,

characterized in that

the transmitter coil (5) and the magnetic field sensor (9) are arranged next to each other, either

the transmitter coil (5) and the magnetic field sensor (9) are arranged next to each other transversely to their main magnetic field axes (5, 11) and the metal object (3) is on the same side of the transmitter coil (3) with respect to the main magnetic field axes (7, 11). 5) and the magnetic field sensor (9) can be arranged, and that

the transmitter coil (5) and the magnetic field sensor (9) have magnetic field main axes (7, 1 1) that are inclined towards one another towards the metal object (3).

2. Inductive sensor according to claim 1, characterized in that the evaluation circuit (9) responds to the first extreme value (33) and / or zero value (37) and / or turning point value occurring in the signal curve of the response signal during the driver pulse (13) and / or to at least one at a predetermined time (ti) according to At the beginning of the driver pulse (13) but still during the driver pulse (13), the amplitude value (S _t ) of the signal curve of the response signal occurs and the information signal representing the material and / or shape parameter depends on the amplitude of the extreme value (33) and / or the to amplitude value (S _t ) occurring at a predetermined time (ti) and/or depending on the time distance of the extreme value (33) and/or the zero value (37) from the start of the driver pulse (13) and/or the signal curve slope of the turning point value.

Sensor according to claim 1, characterized in that the evaluation circuit (19) for the information signal correlates the response signal of the magnetic field sensor with a reference response signal or subjects it to a fast Fourier transformation.

Inductive sensor for detecting a material and/or shape parameter of a metal object (3), comprising

a pulse generator (15),

at least one magnetic field sensor (9) that responds to magnetic fields of the eddy currents induced in the metal object (3) and delivers a response signal dependent on the eddy currents, in particular in the form of a receiving coil and

an evaluation circuit (19) that responds to the response signal and delivers information signal representing the material and/or shape parameters,

characterized in that

a) the transmitter coil (5a-d) and the magnetic field sensor (9a-9d) face each other in the direction of their main magnetic field axes (7a-d, 1 1 ad). are arranged overlying at a distance and the metal object (3a-d) can be inserted between the transmitting coil (5a-d) and magnetic field sensor (9a-d) or

b) the transmitter coil (5) and the magnetic field sensor (9) are arranged next to each other transversely to their main magnetic field axes (5, 11) and the metal object (3) is on the same side in relation to the main magnetic field axes (7, 11). the transmitter coil (5) and the magnetic field sensor (9) can be arranged, and that

the evaluation circuit (19) responds to the first extreme value (33) and/or zero value (37) and/or turning point value occurring in the signal curve of the response signal during the driver pulse (13) and/or to at least one at a predetermined time (ti) after the start of the driver pulse (13) but still occurs during the driver pulse (13) amplitude value (S _t ) of the signal curve of the response signal responds and the information signal representing the material and / or shape parameter depends on the amplitude of the extreme value (33) and / or the predetermined Time (ti) occurring amplitude value (S _t ) and / or depending on the time distance of the extreme value (33) and / or the zero value (37) from the start of the driver pulse (13) and / or the signal curve slope of the turning point value.

Sensor according to claim 4, characterized in that the transmitter coil (5) and the magnetic field sensor (9) have magnetic field main axes (7, 11) which are inclined towards one another towards the metal object (3).

Sensor according to one of claims 1 to 5, characterized in that the transmitter coil (5) and/or the magnetic field sensor (9) are assigned magnetic shielding means, in particular eddy current shielding means (41, 43), which protect the magnetic field sensor (9) against anything directly crossing At least partially shield the magnetic field of the transmitter coil (5).

7. Sensor according to claim 6, characterized in that a shielding wall (41) is arranged between the transmitting coil (5) and the magnetic field sensor (9) and / or the transmitting coil (5) and / or the magnetic field sensor (9) in one direction The shielding cup (43) is arranged which is open to the main magnetic field axes.

8. Sensor according to claim 7, characterized in that the shielding wall (41) and / or the shielding cup (43) consists of non-ferromagnetic metal.

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9. Sensor according to one of claims 1 to 8, characterized in that the magnetic field sensor (9) is assigned a further transmission coil (45) which can be excited by driver pulses (13), the magnetic field of which directly passes over the magnetic field of the transmission coil (5) on the magnetic field sensor (9). i 5 compensates, or at least weakens it.

10. Sensor according to one of claims 1 to 9, characterized in that on the side of the transmitting coil (5) and / or the magnetic field sensor (9) facing away from the metal object (3) there is a compensation sheet metal part (47) for the zero value compensation of the response signal is arranged.

1 1 . Sensor according to one of claims 4 to 10, characterized in that either on the side 5 of the transmitting coil (5b) facing away from the magnetic field sensor (9b) at a distance from the transmitting coil (5b).

Magnetic field sensor (9b ¹ ) is arranged in particular in the form of a further receiving coil and a reference metal object (3b') is arranged between the transmitting coil (5b) and the further magnetic field sensor (9b ¹ ), in which the transmitting coil (5b) indu-0 eddy currents decorated, to whose magnetic field the further magnetic field sensor (9b ¹ ) responds, the evaluation circuit responding to response signals from the magnetic field sensor (9b) and the further magnetic field sensor (9b ¹ ), or that on the side of the magnetic field sensor (9c) facing away from the transmitting coil (5c), a further transmitting coil (5c') which can be excited by drive pulses from the pulse generator is arranged at a distance from the magnetic field sensor (9c) and between the magnetic field sensor (9c)

5 and the further transmitter coil (5c'), a reference metal object (3c ¹ ) is arranged, in which the further transmitter coil (5c') induces eddy currents, to whose magnetic field the magnetic field sensor (9c) also responds, the evaluation circuit depending on the information signal the difference between the response signals of the transmitter coils and the reference value.

12. Sensor according to one of claims 4 to 1 1, characterized in that a reference metal object (3d ') is additionally arranged between the transmitter coil (5d) and the magnetic field sensor (9d), in which the magnetic field of the in the metal object (3d).

Eddy currents in turn induce eddy currents to which the magnetic field sensor (9d) responds or in which the magnetic field of the transmitting coil (5d) induces eddy currents, the magnetic field of which in turn induces the eddy currents in the metal object (3d), to whose magnetic field the magnetic field sensor ( 9d) addresses.

13. Sensor according to one of claims 1 to 12, characterized in that the metal object is a metal sheet or metal foil object.

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14. Sensor according to one of claims 1 to 13, characterized in that the transmitting coil (5) and the receiving coil (9) are designed as air coils.

Sensor according to one of claims 1 to 14, characterized in that the evaluation circuit (19) has an amplifier (21) with a gain factor that decreases non-linearly as the received signal amplitude increases.