Proximity switch and method for detecting an object to be detected

Abstract

The present invention relates to a proximity switch (200) having an oscillating circuit (16) for detecting an object (1) to be detected, characterized in that the oscillating circuit (16) has a resonance frequency in the range from 0.8 MHz to 20 MHz. The present invention also relates to a method for detecting an object (1) to be detected.

Description

Technical Field

[0001] The present invention relates to a proximity switch, a method for detecting an object to be detected, and a use of a frequency range for a detection signal. In particular, the present invention relates to the fields of proximity switches and automation technology. Background Art

[0002] Proximity switches are particularly used in automation technology to detect whether an object to be detected is present. For example, this can be used in a production facility to detect whether an object to be detected is present in order to perform one or more working steps on the object when the object is present.

[0003] Typically, proximity switches are based on electromagnetic, especially capacitive and / or inductive detection of the object to be detected, where the proximity switch has an oscillator circuit by means of which a detection signal is transmitted and as long as it exists, the received signal is received, amplified and evaluated. Due to the electromagnetic interaction between the object to be detected located nearby and the detection signal and the reflected signal returned by the object, it can be determined whether the object to be detected is present based on the received signal. This usually requires the object to be detected to be made of a metallic material or at least mostly made of a metallic material, because in other cases the electromagnetic interaction of the object with the proximity switch, for example inductive interaction, is too small and the proximity switch cannot recognize the object to be detected.

[0004] Conventional proximity switches are known, for example, from document EP 1 526 645 A1. Thus, conventionally, the use of proximity switches in the detection of metallic objects is limited. If a metallic object now approaches the proximity switch, eddy currents are generated in the object. These eddy currents generate a field opposite to the excitation field. This opposite field has different intensities in the receiving coil of the proximity switch. Therefore, voltages of different magnitudes are induced in the two receiving coils by this opposite field. The differential signal of these two voltages is not zero and can be amplified to form an output signal. Thus, the metallic object serves as a trigger for the proximity switch. Summary of the Invention

[0005] The object of the present invention is to provide a proximity switch and a method suitable for detecting an object made of a carbon material or at least partly composed of a carbon material.

[0006] The above object is achieved according to the present invention by a proximity switch, a method and a use having the features of the respective independent claims. Advantageous designs are given in the dependent claims and in the description.

[0007] In a first aspect, the present invention relates to a proximity switch having an oscillator circuit for detecting an object to be detected, wherein the proximity switch is characterized in that the oscillator circuit has a resonance frequency in the range of 0.8 MHz to 20 MHz.

[0008] On the other hand, the present invention relates to a method for detecting an object to be detected by means of a proximity switch. The method includes emitting a detection signal with a frequency in the range of 0.8 MHz to 20 MHz by means of the proximity switch.

[0009] On the other hand, the present invention relates to the use of a frequency in the range of 0.8 MHz to 20 MHz for a detection signal for detecting an object to be detected by means of a proximity switch.

[0010] The fact that the resonant circuit has a resonant frequency in the range of 0.8 MHz to 20 MHz means here that the resonant frequency is within the given range. This does not require that the oscillating circuit must be excitable to resonance throughout the given range, but only that the resonant frequency is within the given range. The resonant frequency can, for example, represent a narrowband frequency range that is completely within the given range. The given range of the resonant frequency does not exclude the possibility that higher harmonic oscillations of the resonant frequency may exceed the given range. The resonant frequency is here the frequency at which the oscillating circuit can be excited and at which the oscillating circuit can emit and receive electromagnetic waves.

[0011] The method for detecting an object to be detected preferably is based on the fact that a detection signal is emitted by means of a proximity switch, in particular with the resonant frequency of the oscillating circuit of the proximity switch. As long as there is an object to be detected in the vicinity of the proximity switch, i.e., in the detection area, an electromagnetic, in particular capacitive, interaction occurs, such that a reflected signal is generated, which can then be detected and evaluated by the proximity switch.

[0012] The carbon material is here in particular a material that consists at least in part and preferably completely of carbon fibers. Carbon fibers are industrially manufactured fibers made from carbon-containing raw materials. Compared to steel, carbon fibers have advantageous properties in terms of weight and strength and are therefore often used for manufacturing parts. Carbon fibers are generally tensile, bend-resistant, and corrosion-resistant. Carbon fibers generally maintain these properties up to 2500 °C in the absence of oxygen. The density of carbon fibers is 1.8 g / cm 3 , while the density of aluminum is 2.7 g / cm 3 , and the density of steel is 7.8 g / cm 3 . Other advantages are the good electrical and thermal conductivity of carbon fibers or carbon materials. The carbon material can also exist as carbon fiber reinforced plastic, carbon fiber reinforced plastic (CFK) or also simply (colloquially) as carbon fiber. Carbon fiber reinforced plastic is here a composite material in which carbon fibers are embedded in a plastic matrix. The matrix serves to connect the fibers and fill the gaps. Epoxy resin material is usually selected as the matrix. However, other thermosetting or thermoplastic plastics can also be used as the matrix material.

[0013] The present invention offers the following advantages and is also capable of detecting or probing the following objects, where the objects are at least partially or even completely composed of carbon material or at least partially composed of such carbon material. In other words, according to the present invention, the detection of the object to be detected does not require the object to be detected to be at least partially or even completely composed of metal material. More precisely, the present invention provides the possibility of reliably identifying objects composed of carbon material.

[0014] The range of resonance frequencies from 0.8 MHz to 20 MHz offers the following advantages: within this frequency range, particularly effective eddy currents can be generated in carbon materials, and accordingly, this frequency range is particularly well-suited for probing objects composed of carbon materials. In addition, this region for the resonance frequency also allows the detection or probing of objects composed of metal materials, such as steel.

[0015] Furthermore, the present invention has the following advantage: objects composed of carbon material can also be reliably identified with a switching distance typical for the case of metal objects. For example, the switching distance can be in the range of 1 mm to 10 mm, and preferably, the switching distance can be in the range of 5 mm to 40 mm. The switching distance can be related to the design of the proximity switch here, for example, related to the diameter of the housing and / or the diameter of the transmitting coil and / or the receiving coil. This offers the advantage that the product device does not have to be changed to a smaller switching distance and there is also no increased risk of collision due to a small switching distance.

[0016] In addition, the present invention offers the following advantages: the proximity switch according to the present invention and the method according to the present invention are not only suitable for probing objects composed of carbon fiber, but also work reliably for detecting objects to be detected composed of metal materials. This offers the advantage that the proximity switch is suitable for probing objects composed of carbon fiber and also for detecting objects composed of metal materials. This makes the replacement of the proximity switch and / or the change of the switching distance obsolete during the production change from metal objects to carbon material objects and vice versa, thereby enabling significant cost savings.

[0017] The present invention runs counter to the hitherto views and expectations of those skilled in the art, since there are sometimes good reasons for using a significantly lower frequency in the range from 200 kHz to 600 kHz for proximity switches. On the one hand, this is because this lower frequency range is suitable for detecting metallic materials, especially steel; on the other hand, because using a frequency above 600 kHz can be disadvantageous and places higher requirements on the proximity switch. For example, higher frequencies are generally avoided in order to avoid the generation of dead zones and / or secondary switching points and to reduce the negative influence from a (non-detectable) metallic environment, which can have a negative impact on the sensitivity. However, the inventors have recognized that using a higher frequency has advantages and is particularly advantageous for detecting objects made of carbon materials.

[0018] Preferably, the resonant frequency of the oscillating circuit lies in the range from 1 MHz to 20 MHz, more preferably in the range from 1 MHz to 14 MHz. This frequency range offers the advantage that it is particularly well-suited for detecting objects made of carbon materials.

[0019] The proximity switch preferably comprises at least one first transmitting coil, a second transmitting coil and a capacitor, wherein the first transmitting coil, the second transmitting coil and the capacitor form an oscillating circuit. Additionally, it is preferably also provided that a separate receiving coil is formed for the transmitting coil, which serves as a receiving coil device. Preferably, the second transmitting coil is arranged relative to the first coil such that the eddy current field caused by the detection signal affects the second transmitting coil in the object to be inspected in the least possible way. In other words, it is advantageous if the second coil of the receiving coil device is arranged almost unaffected by the eddy current field. This can be achieved in such a way that the first and second transmitting coils enclose a certain angle relative to each other and are preferably arranged at right angles to each other. Preferably, the first and second transmitting coils are configured in the same way or even identically and only differ in their arrangement or orientation. The same preferably applies correspondingly to the receiving coils.

[0020] Preferably, the first transmitting coil and / or the second transmitting coil, preferably the first transmitting coil and the second transmitting coil are each configured as a printed transmitting coil. This has the advantage on the one hand that the coils can be manufactured with little effort and at low manufacturing costs. In addition, this offers the advantage that the transmitting coils can be manufactured with a very low inductance. This is particularly advantageous in that, for the matching of the oscillating circuit with respect to the resonant frequency in the range from 0.8 MHz to 20 MHz, the coils have a very low inductance factor. For example, the first and second coils are configured to have an inductance factor in the range from 0.4 μH to 4 μm, for example.

[0021] Preferably, the first transmitting coil and / or the second transmitting coil has an inductance rate in the range of 0.4 μH to 4 μH. Preferably, the capacitor has a capacitance rate in the range of, for example, 22 pF to 2200 pF.

[0022] Preferably, the proximity switch further includes an oscillator or a generator for exciting the oscillation circuit and / or an amplifier for amplifying the received signal received by the oscillation circuit. Preferably, the amplifier has at least one filter stage and at least one capacitive element, and the filter stage and the capacitive element are matched to the resonance frequency of the oscillation circuit. For example, one or more filter stages may be designed to amplify or forward signals within a desired frequency range and filter out frequencies outside of that range. The generator or oscillator is preferably adjusted to excite the oscillation circuit to generate electromagnetic waves in the range of 0.8 MHz to 20 MHz, preferably 1 MHz to 20 MHz, and most preferably 1 MHz to 14 MHz.

[0023] Preferably, the amplifier and / or the generator are designed to reduce the external capacitive influence on the phase position of the excitation of the oscillation circuit. In other words, the amplifier is preferably designed to effect the excitation of the oscillation circuit such that external influences may not have an effect on the amplitude, frequency, and phase position of the excitation signal and accordingly on the electromagnetic radiation emitted by the oscillation circuit.

[0024] The features and embodiments mentioned above and arising below are hereby disclosed not only in the form of the combinations mentioned in detail separately, but also in other technically meaningful combinations and embodiments are included in the disclosure.

[0025] Other details and advantages of the present invention are now explained in detail with reference to the following examples and preferred embodiments with reference to the drawings. Description of the Drawings

[0026] The drawings show:

[0027] Figure 1 A schematic diagram showing the basic principle of a proximity switch as described, for example, in EP 1 526 645 A1;

[0028] Figure 2 A schematic diagram showing a proximity switch according to a preferred embodiment;

[0029] Figure 3 A schematic diagram showing the operating principle for using a proximity switch according to a preferred embodiment.

[0030] In the following drawings, the same or similar elements are denoted by the same reference numerals in different embodiments for simplicity. Detailed Description

[0031] InFigure 1 Shows the basic principle of a proximity switch 100 having two coil pairs, where each coil pair respectively has a transmitting coil S1, S2 and a receiving coil E1, E2. The coils together with capacitors form electromagnetic oscillation circuits.

[0032] The first coil pair is formed by the transmitting coil S1 and the receiving coil E1. These two coils are arranged coaxially with respect to each other and have the same winding direction. Functionally spaced apart from the first coil pair is a second coil pair, which consists of a compensating coil S2 and a second coil E2 of the receiving coil device. The compensating coil is connected in series with the transmitting coil S1 while the second coil of the receiving coil device is connected in series with the first coil E1 of the receiving coil device. The compensating coil S2 and the second coil E2 of the receiving coil device are also placed on each other and arranged coaxially with respect to each other. However, these two coils are wound in opposite directions. The transmitting coil device composed of the two coils S1 and S2 is connected to the generator 2. The generator 2 feeds the two coils S1 and S2 with an alternating voltage. The excitation magnetic field emitted by the transmitting coil S1 generates eddy currents in the metal trigger 1 (e.g., in the object to be detected), and the metal trigger is close to the transmitting coil S1. These eddy currents generate a reverse field with respect to the excitation magnetic field. The eddy current field is superimposed on the excitation magnetic field generated by the transmitting coil S1 in the receiving coil E1. Since the directions of these two fields are opposite, the effective magnetic field present in the receiving coil E1 becomes weaker. This has the result that a slightly smaller voltage is induced in the receiving coil E1.

[0033] A magnetic field is generated by the second transmitting coil S2 previously referred to as the compensating coil. This magnetic field induces a voltage in the second receiving coil E2. The two receiving coils E1 and E2 cooperate with the two transmitting coils S1 and S2 such that the differential output signal is exactly zero when the trigger 1 is at a distance. This is achieved by the fact that in one of the two coil pairs (e.g., S1, E1), the two windings have the same winding direction and in the other coil pair (e.g., S2, E2) the two coils are wound in opposite directions.

[0034] The coil pair having the compensating coil S2 is arranged such that the coil pair is almost not affected by eddy currents. This has the result that the differential output signal 3 does not have a reduced share compared to the prior art, but rather consists essentially of the inductive part generated by the eddy current field.

[0035] Figure 2 Shows a proximity switch according to a preferred embodiment of the present invention. In Figure 2In the embodiment shown in FIG. 1 , the two transmitting coils S1 and S2 form an oscillating circuit with a capacitor K, the oscillating frequency of which is in the range of 0.8 MHz to 20 MHz, for example 7 MHz. The oscillating frequency is excited by the output signal of the amplifier 7. The input signal of the amplifier is the differential voltage signal at the point 3 of the two receiving coils E1 and E2. The output signal of the amplifier is not only fed back into the oscillator or the oscillating circuit, but also reaches the limit value switch 8 which provides the output signal via a filter stage, wherein the filter stage works as a low-pass filter 10. Figure 2 The circuit shown in can be set so that the system also oscillates when the trigger 1 is far away. When approaching the trigger, the transmission field or the detection signal weakens or is disturbed, so that the oscillation is suddenly interrupted. The opposite working method is also possible. In the initial position, the system does not oscillate when it is far away from the trigger. When the trigger approaches the transmitting coil S1, the trigger starts to oscillate.

[0036] The filter stage is designed in this case so that its low-pass filter function is adapted to the resonant frequency of the oscillating circuit in order to filter out the frequency of the oscillating circuit as effectively as possible and obtain a differential signal in a form that is as separated as possible. High resonant frequencies in the range of 0.8 MHz to 20 MHz offer the advantage that the proximity switch is suitable for detecting objects made of carbon material, which is not possible with conventional proximity switches with frequencies between 200 kHz and 600 kHz.

[0037] Figure 3 A schematic diagram of the functional principle of a proximity switch 200 is shown, which is used for use according to a preferred embodiment. The proximity switch comprises a coil 12, which may have a ferromagnetic core, and a capacitor 14. The coil 12 and the capacitor 14 together form an oscillating circuit 16, which may be oscillating with the aid of an oscillator or a generator 18 for oscillation. By determining the dimensions of the coil 12 and the capacitor 14, the oscillation frequency or resonant frequency of the oscillating circuit 16 can be determined. Here, the inductance of the coil 12 and the capacitance of the capacitor 14 are determined so that the resonant frequency of the oscillating circuit 16 is in the range of 0.8 MHz to 20 MHz. This makes the second proximity switch 200 well suited for detecting objects made of carbon material.

[0038] The amplitude of the oscillator 18 is ascertained in a known manner by means of a limit value switch 20, wherein the limit value switch 20 generates a switching signal. The switching signal is then provided by an amplifier 22 to an output 24 for further processing.

[0039] Reference numerals list

[0040] 100 Proximity switch

[0041] 200 Proximity switch according to a preferred embodiment

[0042] S1 and S2 transmitting coils

[0043] E1 and E2 receiving coils

[0044] Q capacitor

[0045] 1 trigger or object to be detected

[0046] 2 generator

[0047] 3 differential signal output terminal

[0048] 7 amplifier

[0049] 8 boundary value switch

[0050] 10 low-pass filter

[0051] 12 coil

[0052] 14 capacitor

[0053] 16 oscillator circuit

[0054] 18 oscillator or generator

[0055] 20 boundary value switch

[0056] 22 amplifier

[0057] 24 output terminal

Claims

1. A proximity switch (200) having an oscillator circuit (16) for detecting an object (1) to be detected, the oscillator circuit (16) detecting the object (1) made of a carbon material based on a change in the amplitude of a detection signal, wherein the carbon material is at least partially composed of carbon fibers, wherein the proximity switch (200) includes a first coil pair and a second coil pair, wherein the first coil pair and the second coil pair are arranged perpendicular to each other, the oscillator circuit (16) has a resonance frequency in the range of 1 MHz to 20 MHz, and wherein the object (1) made of a carbon material can be reliably identified at a switching distance typical for metal objects.

2. The proximity switch (200) according to claim 1, wherein the resonance frequency of the oscillator circuit (16) is in the range of 7 MHz to 14 MHz.

3. The proximity switch (200) according to claim 1 or 2, wherein the first coil pair includes a first transmitting coil (S1) and a first receiving coil (E1), the second coil pair includes a second transmitting coil (S2) and a second receiving coil (E2), and wherein the oscillator circuit (16) is formed by the first transmitting coil (S1), the second transmitting coil (S2), and a capacitor (K, 14).

4. The proximity switch (200) according to claim 3, wherein at least one of the first transmitting coil (S1) and the second transmitting coil (S2) is configured as a printed transmitting coil.

5. The proximity switch (200) according to claim 3, wherein both the first transmitting coil (S1) and the second transmitting coil (S2) are configured as printed transmitting coils.

6. The proximity switch (200) according to claim 3, wherein the inductance of at least one of the first transmitting coil (S1) and the second transmitting coil (S2) is in the range of 0.4 μH to 4 μH; and / or wherein the capacitance of the capacitor (K, 14) is in the range of 22 pF to 2.2 nF.

7. The proximity switch (200) according to claim 6, further comprising an amplifier (7) for amplifying a received signal received by the oscillator circuit (16), wherein the amplifier (7) has at least one filter stage and at least one capacitive element, the filter stage and the capacitive element being matched to the resonance frequency of the oscillator circuit (16).

8. The proximity switch (200) according to claim 7, wherein the amplifier is designed to reduce an external capacitive influence on the phase of the excitation of the oscillator circuit (16).

9. A method for detecting the object (1) to be detected by means of the proximity switch (200) according to claim 1, the method comprising transmitting a detection signal having a frequency in the range of 1 MHz to 20 MHz by means of the proximity switch (200).

10. Use of a frequency in the range from 1 MHz to 20 MHz for detecting a signal, the detection signal being used to detect the object (1) to be detected by means of the proximity switch (200) according to claim 1.

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