Method and apparatus for detecting pressure on a metallic surface

Abstract

Method for detecting pressure exerted by an operator on a surface of an operating area (1.7) provided with a metallic layer, preferably a metallic coating (1.2), comprising the steps: - Placing at least one coil (3.2) integrated into an electronic circuit below the operating surface (1.7), - Applying a supply voltage (3.3) controlled by a control pulse (3.6) to at least one coil (3.2), - Generating a recoil pulse (3.5) during a pulse pause of the control pulse (3.6) by means of the at least one coil (3.2) and allowing the recoil pulse (3.5) to oscillate, characterized in that a region (5.1) after the recoil pulse (3.5) and before the oscillation (5.2) of the recoil pulse, which is longer in time than the individual oscillations of the oscillation (5.2), is correlated with the pressure exerted by the operator, wherein a temporal length (5.9) of the region (5.1) is in relation to the pressure exerted by the operator.

Description

[0001] The invention relates to a method for detecting pressure exerted by an operator on a surface of an operating area provided with a metallic layer, preferably with a metallic coating, with the features of claim 1, and to a device for detecting pressure exerted by an operator on such a surface with the features of claim 11.

[0002] A "metallic layer" or "metallic coating," terms used synonymously in these documents, refers to a metallic area on a control surface. This metallic area can be formed by a metallic layer on a substrate material, regardless of how it is applied. The metallic area can also be metallized, for example, by applying a metallic coating to a substrate such as plastic, e.g., through electroplating. Alternatively, the metallic area can be part of a partially or fully metallic control element. State of the art

[0003] Since mechanical switches are operated by touching a metallic, e.g., galvanized, surface, efforts are made to make the surface as wear-resistant as possible, for example, by chrome plating. For aesthetic reasons, the surface into which these switches are recessed is usually also chrome-plated. A disadvantage of such switches is the need to move them mechanically relative to the adjacent surface in order to, for example, trigger an electrical contact. This inevitably creates a gap between the surface and the moving element of the switch. Dirt can accumulate in this gap over time, making the movement of the switch element stiff. Furthermore, the moving element must be mechanically guided along its path, which requires installation space. Behind the mechanical element is the assembly containing the electrical contact.This can be opened or closed when the switch is operated, but it gives no indication of the pressure exerted on the control element.

[0004] Switching elements that use a change in the capacitance of a sensor electrode to trigger a switching process can be implemented very flat and without mechanical movement, but do not work under closed metal surfaces.

[0005] In a capacitive sensor used as a switching element, a conductive electrode surface is typically located approximately on the surface of the control element, beneath it and insulated from its surroundings. Insulated means that the electrode surface is mounted under a non-conductive material and is not visible to the user. The surface of the control element can also be coated with a non-conductive lacquer and / or marked with appropriate operating symbols. Manual contact with this area changes the capacitance of the electrode surface, which is then evaluated by the corresponding electronics. The disadvantage of this solution is that the plastic or lacquer surface is not very hard, so noticeable signs of wear can appear after prolonged use.

[0006] If capacitive controls with a conductive metal surface are to be used, the control area must be electrically isolated from any surrounding metal surface. This means the control surface must be electrically or capacitively connected to the evaluation electronics, while the surrounding metal surface is usually at zero potential or grounded. While wide insulating areas between the control and the metal surface are advantageous for electrical function, they can be aesthetically displeasing. Conversely, narrow insulating areas, which might be aesthetically pleasing, can cause even small, slightly conductive contaminants to connect the control surface to the surrounding metal, thus disabling the capacitive switch. Recessed insulating areas are even more problematic.While this can significantly improve the appearance, experience shows that dirt quickly accumulates here and the switch can lose its function.

[0007] Another disadvantage arises when electroplating a plastic substrate. The insulated areas of the operating elements must be electrically contacted during electroplating, which results in a considerable increase in manufacturing effort.

[0008] However, unintentional activation of a switch is also a disadvantage. Even accidentally touching or unintentionally leaning against a capacitive switch can trigger it. This is particularly critical when used in a vehicle.

[0009] Furthermore, problems arise when operating the device with thick gloves, as the capacitive influence may be too weak through the glove.

[0010] WO 2020 / 025608 A1 discloses an inductive method in which the crystalline change under pressure on a metal surface is measured using a ramp-shaped controlled current and a corresponding coil arrangement. While an inductor beneath a closed metallized user interface is used to implement a control element, a complex circuit architecture is employed.

[0011] DE 10 2019 132 508 A1 discloses a capacitive sensor device and a method for detecting the approach and / or position of at least one object. For this purpose, at least one measuring electrode is provided on a sensor-active area. By means of a control device, the measuring electrode is driven by a voltage derived from a supply voltage, thereby generating an electric field that extends from the measuring electrode into the sensor-active area. A switching device, which can be actuated by the control device, is operatively connected to the measuring electrode for generating the electric field. An evaluation device is provided for evaluating the changes generated by the measuring electrode as a result of the movement and / or presence of the object in the sensor-active area.At least one inductor is arranged between the voltage source and the switching device, wherein the control device, due to the inductance, controls the switching device when the current is switched off to generate a backflip pulse with high-frequency spectral components, which generates a voltage at the measuring electrode that is higher than the supply voltage.

[0012] German patent application DE 10 2018 117 901 B3 describes a capacitive proximity sensor and a method for determining the approach of an object to the sensor arrangement. The capacitive proximity sensor comprises a sensor arrangement with a resonant circuit containing an inductor and a capacitance. The capacitance is defined relative to a ground potential. The resonant circuit is excited by an excitation circuit. An output signal, which can be tapped from the resonant circuit, is evaluated by an evaluation circuit to determine the approach of an object. A sensor electrode is integrated into the resonant circuit as a resonant capacitor. In an initial state, the resonant circuit is excited by the excitation circuit at a frequency below the resonant frequency of the circuit.In this process, a medium with a resistive component, which can be placed between the sensor electrode and the ground potential, causes a detuning of the resonant circuit, resulting in an output signal with an amplitude that remains constant or nearly constant compared to the initial state. Conversely, the approach of an additional capacitance to the sensor electrode leads to a detuning of the resonant circuit, resulting in an output signal with an amplitude that differs from the initial state, even in the presence of the medium with a resistive component. The evaluation circuit detects the approach of the additional capacitance by the change in the amplitude of the output signal. This capacitive proximity sensor, or rather the method itself, does not react to moderately conductive coatings such as a continuous film of water, damp dirt, snow, or ice, even if these coatings are connected to the electrical ground potential and partially or completely cover the sensor electrode.Thus, a hand approaching can be clearly detected through these grounded coverings.

[0013] DE 10 2018 211 025 A1 discloses an electronic device with a housing and an actuating element movable relative to the housing, wherein the actuating element comprises at least one metallic component. The device further comprises an inductive sensor for detecting the position and / or movement of the actuating element. The inductive sensor includes a first measuring resonant circuit with a sensor coil, in which a first measuring oscillation can be generated, and a vibration generator that generates an excitation oscillation and at least temporarily applies the excitation oscillation to the first measuring resonant circuit. The device also includes an evaluation unit that determines motion information characterizing the position and / or movement of the actuating element as a function of the first measuring oscillation. Summary of the invention

[0014] Based on this state of the art, the object of the invention is to provide a method for detecting pressure on a metallized surface and a device with a metallized surface that allows the actuation of the control element behind a metallic surface to be interference-free.

[0015] This problem is solved by a method and a device for detecting pressure exerted by an operator on a surface of an operating area provided with a metallic layer, having the features of claim 1 or of claim 11.

[0016] According to the method, at least one coil integrated into an electronic circuit is arranged below the operating surface. This coil is provided with a metallic layer or coating, or has a metallized surface. A supply voltage is applied to the coil by means of a periodic or aperiodic control pulse. This generates a recoil pulse during a pulse pause of the control pulse, which then oscillates. A period of time after the recoil pulse and before its decay, which is longer than the individual oscillations of the decay, is then correlated with the pressure exerted by the operator, with the duration of this period being proportional to the pressure exerted by the operator.

[0017] Based on the prior art, industry generally desires operating elements concealed behind a preferably closed, metallic surface. In the context of this application, "closed" means that there are no isolated areas within the operating surface, and the user perceives only a continuous metal surface with printed or laser-etched symbols for the operating functions. Preferably, the surface can be chrome-plated, as this advantageously provides an attractive appearance while also being durable. The symbols must be mechanically activated by pressing, as with a conventional switch, which advantageously prevents accidental activation.

[0018] The present solution advantageously detects the effects of even slight operator pressure using a circuit built with only a few electronic components, ensuring interference-free detection. Interference-free detection means reliably detecting even very small changes in the coil's inductance despite significant interference, such as that which can occur in automotive applications. This is achieved by advantageously utilizing a backflip pulse as a high-amplitude pulse, several times greater than the expected interference signals.

[0019] The problem is also solved by a device for detecting pressure exerted by an operator on such a surface of a control panel, which is configured to carry out the method. It has at least one coil located below the control panel near the metallic layer or coating, which generates a recoil pulse during a pulse pause of a control pulse. A detection device detects a period after the recoil pulse and before the recoil pulse's decay, which is longer in time than the individual oscillations of the decay, and correlates it with the pressure exerted by the operator, whereby the duration of this period is proportional to the pressure exerted by the operator. The advantages of the method are thus realized.

[0020] Advantageous further developments are the subject of the dependent patent claims. The features listed individually in the patent claims can be combined with one another in a technologically meaningful way and can be supplemented by explanatory facts from the description and by details from the figures, thereby showing further embodiments of the invention.

[0021] Preferably, the duration of the area is directly and linearly related to the pressure exerted by the operator, so that the exerted pressure can be read directly without the need for a complex algorithm.

[0022] In a preferred embodiment, a digital signal indicating analog voltage changes at the coil is output at the electronic circuit output, so that a switching signal triggered by an operator can be advantageously and easily detected.

[0023] Preferably, compared to the prior art, a simple circuit with only one coil per operating function is located below the operating surface. This advantageously makes the circuit inexpensive and insensitive to temperature influences. Preferably, a measurement of the time interval with increased resolution can also be performed only towards the end of the interval, since the variation in this interval represents only a small fraction of the total interval. Therefore, a fixed time can elapse before the actual measurement, after which the actual high-resolution measurement is advantageously performed within a short period.

[0024] Advantageously, good results have been achieved when the magnitude of the recoil impulse is preferably several times higher than the supply voltage, preferably 20 to 30 times higher than the supply voltage.

[0025] In a preferred embodiment, the operating surface has an area of ​​reduced material thickness in which the at least one coil is arranged in the immediate vicinity of the metallic layer or coating. In this area, the desired minimal deformation can advantageously be detected more easily by sensors.

[0026] Preferably, at least in the area of ​​the operating surface, a metallic layer or coating is also applied to the side of the carrier material facing away from the operator, and this layer is arranged in close proximity to the at least one coil. The additional metallization of the inside of the operating surface advantageously results in a smaller distance between the metal and the coil, which increases the sensitivity of the pressure exerted on the operating surface.

[0027] Preferably, a cavity is formed in the substrate material and / or in a circuit board, in which the at least one coil is arranged. The cavity makes this area easier to deform and also allows the coil to be securely held there.

[0028] Preferably, the thickness of the carrier material is dimensioned such that, under pressure exerted by an operator, a change in the shape of the operating surface occurs that is imperceptible to the human eye. While the operating surface advantageously remains unchanged from the operator's perspective, an actuation can nevertheless be reliably detected.

[0029] The device design offers the same advantages as the method, which should therefore be mentioned.

[0030] Further advantages will become apparent from the following description of a preferred embodiment. Brief description of the characters

[0031] The invention will now be explained in more detail with reference to exemplary embodiments illustrated in the accompanying figures. These show: Fig. 1 a section through a control element, Fig. 2 a section through a control element with a flexible support structure, Fig. 3 a circuit for generating a recoil pulse, Fig. 4 a peak of a backlash impulse, Fig. 5 Signal waveforms of the voltage over time t during a settling-out period after switching off the control pulse, Fig. 6. A representation of possible starting points for a measurement, Fig. 7. An application with multiple switching elements using a multiplexer. Description of preferred embodiments

[0032] Before the invention is described in detail, it should be noted that it is not limited to the respective components of the device or the respective process steps, as these components and processes may vary. The terms used here are intended solely to describe particular embodiments and are not used restrictively. Furthermore, where the singular or indefinite articles are used in the description or in the claims, this also refers to the plural of these elements, unless the overall context clearly indicates otherwise.

[0033] The invention is based on the idea of ​​using an inductive system as a pressure sensor, which will be explained in more detail below.

[0034] If, within the limited area of ​​a control element, a plastic carrier with a metal surface is given a material thickness such that pressure on this area results in a very slight deflection of only a few micrometers, the approach of this area can be detected by a suitably designed inductive sensor. The aim is to create a sensor sensitive enough to reliably detect a change in distance of just a few micrometers.

[0035] The sensor element should preferably consist of only a printed coil with a few turns and be mounted at a distance behind the galvanized plastic substrate. A deflection of a few micrometers on a control surface with, for example, a diameter of 15 mm, does not fatigue the material and is neither visible nor perceptible when pressed with a finger. The distance between the metallization and the coil can, depending on the design, be several millimeters.

[0036] Since the sensor consists of only a single printed coil with a few turns, unlike, for example, WO 2020 / 025608 A1, it—or several of them together—can be mounted on a circuit board. Flexible circuit boards can also be used to allow for, for example, a curved shape of the metallic surface with switching functions. These are then connected to the plastic substrate. The coil areas do not necessarily have to be flush with the metal surface, which allows for greater design freedom.

[0037] The following describes the design of a sensor suitable for the application listed above.

[0038] Since the electronics implementation is only one essential detail of an otherwise common circuit for generating a so-called recoil pulse, the aspects of pulse generation will only be discussed here to the extent necessary for understanding the solution.

[0039] A prerequisite for the invention to function is a coil of any shape, preferably located in the immediate vicinity of the metallized operating surface. The coil can, for example, be a printed coil. It can be, for example, square, rectangular, round, or have another shape, and it can also, for example, have a three-dimensional shape and / or be curved. Fig. Figure 1 shows such an arrangement as a cross-section through a control element 1.7. The control element consists of a carrier material 1.3, the surface of which is provided with a metallic layer, preferably a metallic coating 1.2. For better visibility, the metallic coating is shown significantly thicker in the figures than it actually is. This metallic coating is preferably a chromium coating, but a coating with other metallic materials or material combinations containing metals is also conceivable. It can also be a metallization of, for example, a plastic material as the carrier material 1.3. In principle, however, the metallic layer can also be part of a metallic control element, i.e., part of a metal body that may even consist entirely of metal.

[0040] Below the carrier material 1.3 is a circuit board 1.4 with at least one coil 3.2, from which the Fig. 1 and Fig. 2 Only the partially exposed conductor tracks are indicated. Preferably, exactly one coil is provided for each operating function. The coil can have any two- or three-dimensional shape. A cavity 1.6, approximately the size of the operating area 1.7, is recessed between coil 3.2 and the substrate material 1.3. The thickness, or in the figures height, of the cavity 1.6 can be extremely small; a few µm are sufficient. The cavity 1.6 can be incorporated into the substrate material 1.3 and / or be part of the circuit board 1.4.

[0041] The thickness of the carrier material 1.3 above the coil 3.2 can be selected such that finger pressure on this area does not cause any indentation or deformation visible to the human eye. This was the case with common carrier materials and a diameter of 12 millimeters for the control element with a material thickness of approximately one to two millimeters.

[0042] If a slight pressure, i.e., of a few tens of mPa corresponding to a weight force of a few grams, is now exerted on the area above the cavity 1.6, the crystalline structure of the surface of the metallic layer or coating 1.2 is affected, or the surface of the operating area 1.7 bends minimally towards the coil 3.2. This bending is so small that it is generally not perceptible to the human eye.

[0043] The circuit board 1.4 and the substrate material 1.3 can be bonded together or otherwise connected in any other way. A strong bond (bonding) is advantageous if curved or otherwise structured operating surfaces are desired for design reasons. In this case, a flexible circuit board 2.4 can be used according to... Fig. 2 adapt easily to the contours of the substrate.

[0044] The present solution is designed to advantageously detect the effects of slight operator pressure using a circuit built with only a few electronic components, ensuring interference-free detection. Interference-free detection means reliably detecting even the very small changes in the inductance of coil 3.2 despite significant interference, such as that which can occur in automotive applications.

[0045] One possibility is to use the highest possible pulse, whose amplitude is several times that of the expected interference signals. A corresponding pulse height can be achieved by a circuit for generating a so-called backfire pulse 3.5 according to [reference to relevant section]. Fig. 3. If the coil 3.2 used for this purpose is placed in the immediate vicinity of the metallized control surface 1.7, even the slightest change in the position of the control surface 1.7 affects the magnitude of the recoil pulse. Since there is a percentage relationship between the signal amplitude in the coil 3.2 and the effect of a change in the metallization's position, it is clear that, for example, a 60 V signal from a recoil pulse 3.5 will exhibit a higher effect, measured in millivolts, due to the change in position than if the signal in the coil 3.2 were only a few volts.

[0046] The circuit according to Fig. Circuit 3.5, which generates a feedback pulse, comprises a switching transistor 3.1 and the coil 3.2. The switching transistor 3.1 is periodically driven, for example, every millisecond, by a 3 µs long control pulse 3.6. In principle, aperiodic control is also possible, as long as it is ensured that a pause without a control pulse or pulse pause follows each control pulse 3.6, during which a feedback pulse 3.5 and a decay can occur. During the control pulse 3.6, a current flows in the coil 3.2 and builds up a magnetic field. After the control pulse 3.6 is switched off, a feedback pulse 3.5 occurs at the coil 3.2 with a significantly higher amplitude than the supply voltage 3.3. 3.4 corresponds to ground potential. The magnitude of the recoil pulse 3.5 depends on the coil characteristics, the supply voltage 3.3, and the length of the control pulse 3.6. The length of the control pulse 3.6 can be chosen so that the magnitude of the recoil pulse is, for example, 60V.

[0047] The amplitude of the feedback pulse 3.5 also depends on the presence of metal in front of coil 3.2, in this case, the metallic layer or coating 1.2. Due to the pulse amplitude of feedback pulse 3.5 being 60V, any influence on the metallic layer or coating 1.2 will manifest as a relatively large change in pulse amplitude. Relatively large means, for example, a voltage change of 200mV with a typical user press. This is a voltage change that can be easily amplified and evaluated under "normal" circumstances. "Normal" in this case means that this voltage change is within the range of the supply voltage 3.3, i.e., between ground potential and 3.3V. However, this is not the case here, as the voltage change is at a level of 60V, which is difficult to process.

[0048] Fig. Figure 4 shows the peak 4.1 of the recoil impulse, represented by line 4.2, which shows the amplitude of the recoil impulse without pressure on control surface 1.7. When control surface 1.7 is pressed, the peak amplitude decreases slightly, as shown by the dashed line 4.3. The width of the recoil impulse is very small in this case, e.g., < 1 ns. All in all, this is a difficult situation to evaluate.

[0049] The amplitude of the recoil pulse 3.5 can also be influenced by capacitive effects present between the coil 3.2, which serves as the sensor element, and the surface of the metallic layer or coating 1.2. The potential of the metallic layer also has a significant influence. Whether the metallic layer is grounded or not connected to anything makes a clear difference in the amplitude 4.2. Since grounding the metallic coating is often not possible for design reasons, touching it with a hand outside the operating area 1.7 could "ground" the surface of the metallic coating 1.2 and thereby trigger a malfunction. Therefore, evaluating the pulse height is not a useful method.

[0050] Now, an effect is used in which the aforementioned problems surprisingly do not occur. After the recoil impulse 3.5 subsides, an oscillation begins, i.e., a "back-and-forth" oscillation of energy between coil 3.2 and capacitor 3.7. The resonant frequency of the oscillation depends on the self-capacitance of coil 3.5 and the parallel capacitance of capacitor 3.7.

[0051] This is in Fig. Figure 5 shows a signal waveform of the voltage over time t. Before the actual "oscillation" 5.2 begins, the magnetic energy in the coil 3.2 dissipates via a corresponding current flow through the diode 3.15. This diode function is, incidentally, already a standard component of a switching transistor 3.1 and is only included in the circuit diagram for better understanding of its function. A wider region 5.1 is clearly visible before the start of the general oscillation 5.2. This region 5.1 is wider than the individual oscillations of the oscillation 5.2. One reason for this is the dissipation of the energy stored in the coil 3.2. The limitation of the negative amplitude is caused by the diode 3.15 and the characteristics of the switching transistor 3.1.

[0052] When the width of this area 5.1 is measured, a clear correlation emerges with the unpressed and pressed surface of the metallic layer or coating 1.2, i.e., the actuation of the control surface 1.7 becomes apparent. In contrast, the presence or absence of grounding of the metallic coating 1.2 has no effect whatsoever. When pressure is applied to the surface of the metallic coating 1.2, area 5.1 shortens, depending on the strength of the pressure. Therefore, an evaluation provides not only a switching signal but also the value of the analog pressure on the control surface 1.7.

[0053] Fig. Figure 3 shows a simple circuit for evaluating the width of the range 5.1. First, the high amplitude of the feedback pulse 3.5 is kept away from the subsequent electronics. This is achieved by resistor 3.11 and limiting diodes 3.12. Capacitor 3.13 serves only for DC decoupling. The voltage divider, formed by resistors 3.9 and 3.10, generates the reference voltage for comparator 3.8. Capacitor 3.14 suppresses or averages voltage influences caused by the current flow in limiting diodes 3.12 during signal limiting. Thus, comparator 3.8 provides digital information 3.16 at its output regarding the analog voltage changes across coil 3.2.

[0054] Fig. Figure 5 shows the signal waveforms in detail. Line 5.3 visualizes the reference voltage. The dashed lines 5.4 and 5.5 are the voltage limits imposed by the limiting diodes 3.12. The dashed signal waveform 5.6 symbolizes the signal before resistor 3.11, and the solid line 5.7 the limited signal at the input of comparator 3.8. At the output of comparator 3.8 in Fig. The digital output signal 5.8 is located at position 3 on the right. Fig. 5 below, from which area 5.9 is evaluated for variation in time length.

[0055] Line 5.4 is the upper limit voltage, and line 5.5 is the lower limit voltage, formed by the limiter diodes 3.12. The reference voltage 5.3 is typically the midpoint between these two, formed by the voltage divider 3.9 and 3.10. This reference voltage 5.3 is thus the "zero line" for the comparator 3.8, which does not necessarily mean that the reference voltage is 0 V. It should be viewed as a "reference line." For this reason, in Fig. 5. The voltage is also indicated only as V and -V, which are shown in the signal waveform over time t. Ground 3.4 is generally the true zero voltage of the entire circuit. In the exemplary embodiment, the voltage in region 5.1 falls below zero (due to diode 3.15).

[0056] As can be seen in the figures, the area around the reference voltage 5.3 is primarily considered as the "average value". Advantageously, the circuit keeps a rather high voltage resulting from the recoil pulse 3.5 away from the comparator 3.6, which may be sensitive to overvoltage. Only a portion of the voltage between the limiting voltages 5.4 and 5.5 is fed to the comparator 3.8.

[0057] The important point is that this simple circuit immediately generates a digital signal which advantageously contains information about the pressure on the operating surface 1.7, without potential differences or capacitive influences having any effect on the metallization of the operating surface 1.7.

[0058] Further evaluation can now be carried out using exclusively digital processes. Since the starting point 5.10 of area 5.9 does not change over time when pressure is applied to the operating surface 1.7 relative to the control pulse 3.6, the trigger point for starting the measurement can be derived from the beginning or end of the control pulse 3.6 or from the starting point 5.10.

[0059] Fig. Figure 6 shows the possible starting points 6.1 for a measurement. The actual measurement can only begin shortly before the end of the range 5.1, since the variation in this range represents only a small fraction of the entire range. Therefore, a fixed time 6.2 can elapse before the actual high-resolution measurement 6.3 takes place. This may be necessary because the change in the length of range 3.16 at average pressure can only vary by, for example, 200 ns.

[0060] A further advantage results from the additional metallization of the inside of the control surface 1.7. This creates a smaller distance between the metal and the coil 3.2. This increases the sensitivity of the pressure detection on the control surface 1.7.

[0061] This circuit allows any number of switching elements to be implemented with minimal effort using simple means such as the use of Multiplexer 7.3. Fig.Figure 7 shows an example application. Figure 7.1 is a microcontroller (µC) with exclusively digital signal processing, which outputs the control pulse 3.6 periodically or aperiodically and selects the sensor units 7.2, consisting of a switching transistor and an inductor, via multiplexer 7.3. The sensor unit 7.2 represents any number of different inductors and switching transistors. The feedback pulse of the selected sensor unit 7.2 is fed back to the comparator and returned to the microcontroller (µC) as digital information 7.4. Here, the evaluation of temporal changes can be performed on a purely digital basis. Reference symbol list 1.1 Finger Operator 1.2 Metallic layer or coating of the surface 1.3 Carrier material 1.4 Circuit board 1.6 Cavity 1.7 Control surface 2.4 flexible circuit board 3.1 Switching transistor 3.2 Coil 3.3 Supply voltage level 3.4 Ground Potential (Mass) 3.5 Backlash impulse 3.6 Control pulse, 3µs 3.7 Parallel capacitance to the coil 3.8 Comparator 3.9, 3.10 Resistor voltage divider 3.11 Resistance 3.12 Limiter diodes 3.13 Capacitor for DC decoupling 3.14 Capacitor for suppressing the influence of the limiter diodes 3.15 Diode 4.1 Peak of the backlash impulse 4.2 Amplitude without touch 4.3 reduced amplitude 5.1 wider area 5.2 general decay 5.3 Reference voltage 5.4, ​​5.5 Limiting voltage of the limiter diodes 5.6 symbolized signal before resistor 3.11 5.7 Signal at the input of the comparator 5.8 digital output signal 5.9 Area that is evaluated for variation in time length 5.10 Starting point of area 5.9 6.1 Starting point of the measurement 6.2 fixed time 6.3 High-resolution measurement 7.1 µC with exclusively digital signal processing 7.2 Sensor unit 7.3 Multiplexer 7.4 Digital Information

Claims

[1] Method for detecting pressure exerted by an operator on a surface of an operating area (1.7) provided with a metallic layer, preferably a metallic coating (1.2), comprising the steps: - Placing at least one coil (3.2) integrated into an electronic circuit below the operating surface (1.7), - Applying a supply voltage (3.3) controlled by a control pulse (3.6) to at least one coil (3.2), - Generating a recoil pulse (3.5) during a pulse pause of the control pulse (3.6) using the at least one coil (3.2) and allowing the recoil pulse (3.5) to oscillate. characterized by, that a region (5.1) after the recoil impulse (3.5) and before the oscillation (5.2) of the recoil impulse, which is longer in time than the individual oscillations of the oscillation (5.2), is correlated with the pressure exerted by the operator, wherein a temporal length (5.9) of the region (5.1) is proportional to the pressure exerted by the operator. [2] Method according to claim 1, characterized by , that the temporal length (5.9) of the area (5.1) is analogously in a linear direct relationship with the pressure exerted by the operator. [3] Method according to claim 1 or 2, characterized by , that at the output of the electronic circuit a digital information (3.16, 7.4) of analog voltage changes at the coil (3.2) is output. [4] Method according to any one of the preceding claims, characterized by , that exactly one coil (3.2) is placed below the operating surface (1.7) for each operating function. [5] Method according to any one of the preceding claims, characterized by , that a measurement of the temporal length (5.9) of the area (5.1) with increased resolution (6.3) only takes place at the end of the area (5.1). [6] Method according to any one of the preceding claims, characterized by , that the magnitude of the recoil pulse (3.5) is several times higher than the supply voltage (3.3), preferably 20 to 30 times higher than the supply voltage (3.3). [7] Method according to any one of the preceding claims, characterized by , that the operating surface (1.7) has an area of ​​reduced material thickness in which the at least one coil (3.2) is arranged in the immediate vicinity of the metallic layer or metallic coating (1.2). [8] Method according to any one of the preceding claims, characterized by, that at least in the area of ​​the operating surface (1.7) on the side of the carrier material (1.3) facing away from the operator, a metallic layer or a metallic coating is applied, which is arranged in the immediate vicinity of the at least one coil (3.2). [9] Method according to any one of the preceding claims, characterized by , that a cavity (1.6) is formed in the carrier material (1.3) and / or in a circuit board (1.4, 2.4) in which the at least one coil (3.2) is arranged. [10] Method according to any one of the preceding claims, characterized by , that the thickness of the carrier material, in particular if the operating surface (1.7) has an area of ​​reduced material thickness according to claim 7, is dimensioned such that, under pressure exerted by an operator, a change in shape of the surface of the operating surface (1.7) occurs which is not perceptible to the human eye. [11] Device for detecting pressure exerted by an operator on a surface of an operating area (1.7) provided with a metallic layer, preferably with a metallic coating (1.2), configured to carry out the method according to one of claims 1 to 10, comprising at least one coil (3.2) located below the operating area (1.7) in the vicinity of the metallic layer and integrated into an electronic circuit, which is configured to generate a recoil pulse (3.5) during a pulse pause of a control pulse (3.6), characterized by, that a detection device is provided which detects a region (5.1) after the recoil impulse (3.5) and before the oscillation (5.2) of the recoil impulse, which region is longer in time than the individual oscillations of the oscillation (5.2), and correlates with the pressure exerted by the operator, wherein a temporal length (5.9) of the region (5.1) is proportional to the pressure exerted by the operator. [12] Device according to claim 11, characterized by , that exactly one coil (3.2) is provided below the operating surface (1.7) for each operating function. [13] Device according to claim 11 or 12, characterized by , that the operating surface (1.7) has an area of ​​reduced material thickness in which the at least one coil (3.2) is arranged in the immediate vicinity of the metallic layer or metallic coating (1.2). [14] Device according to any one of claims 11 to 13, characterized by, that at least in the area of ​​the operating surface (1.7) on the side of the carrier material (1.3) facing away from the operator, a metallic layer or metallic coating is provided which is arranged in the immediate vicinity of the at least one coil (3.2). [15] Device according to any one of claims 11 to 14, characterized by , that a cavity (1.6) is formed in the carrier material (1.3) and / or in a circuit board (1.4, 2.4) in which the at least one coil (3.2) is arranged. [16] Device according to any one of claims 11 to 15, characterized by , that the thickness of the carrier material is dimensioned such that, under pressure exerted by an operator, a change in shape of the surface of the operating area (1.7) occurs that is not perceptible to the human eye.

Images