Operating element, use thereof and associated detection method

Abstract

The invention relates to an operating element having an operating region and a capacitive sensor device for detecting a proximity and / or touch of an operator to the operating region, the capacitive sensor device has an electrode and a counter electrode for generating a measurement capacitance associated with the capacitive operating region and an analysis unit that can be selectively electrically connected to the electrodes on a side of the operating region facing away from the operator. According to the invention, the capacitive sensing device is designed to carry out a method having at least a plurality of steps, by means of different initial or influencing potentials applied to the electrodes, a potential set at the electrodes after a certain duration, i.e., a first potential or a second potential, is determined; the steps i to viii are repeated a plurality of times in this order, each of which forms a measurement cycle and, after each measurement cycle, a change in the value formed by the first potential and the second potential relative to the old value previously acquired in the previous measurement cycle is determined qualitatively and / or quantitatively by means of the capacitive sensor device.

Description

Field of the Invention

[0001] The present invention relates to an operating element for a capacitive sensing device for detecting proximity and / or touch with better reduction of temperature influence, its application, and a related detection method. Background Art

[0002] In order to recognize user input at an operating element, so-called touch-sensitive operating areas are popular. To recognize a touch, a capacitive sensing device is preferably used because of its relatively high and reliable sensing sensitivity. These capacitive sensing devices associated with the corresponding operating area generally include at least one electrode and an analysis unit connected thereto. Common capacitive sensing devices for this purpose include expensive special hardware components such as tilt oscillators (Kipp-Oszillatoren), comparators. A sensing device that does not use such components is known, for example, from US 8 836 350 B2. In addition to electromagnetic interference, which is a relatively easy-to-control problem related to capacitive sensing devices, additional problems caused by the temperature sensitivity of the sensing device have also emerged in practice. Especially in motor vehicles, capacitive sensing devices are exposed to large temperature fluctuations, which cause a large change in the measured capacitance associated with the operating area and may lead to false detections under expected user inputs, which is called "ghost touch". For manufacturing process reasons and due to simplified electrical contacts, such measured capacitance is achieved by a metal coating forming one or more electrodes on a foil substrate, which is typically arranged on the side of the panel facing away from the operator. Here, the expansion and position changes caused by temperature cannot be completely suppressed mechanically. Therefore, there is a need to offset the change in the measured capacitance caused by temperature changes, which is also simply referred to as temperature compensation here. Summary of the Invention

[0003] In this context, the basic object of the present invention is to provide an operating element for a capacitive sensing device for detecting proximity or touch, which in addition to precise detection also ensures that the influence of temperature on detection is minimized, can be implemented at low cost in particular, and has a low complexity. This object is achieved by an operating element having the features of claim 1 and by a method having the features of the independent claims in parallel. The corresponding dependent claims disclose other particularly advantageous design solutions of the present invention.

[0004] It should be noted that the features described separately in the following description can be combined with each other in any technically meaningful way and exhibit other design solutions of the present invention. In addition, the description characterizes and details the present invention in particular in conjunction with the accompanying drawings.

[0005] It should further be noted that the conjunction "and / or" used hereinafter in this text to connect two features and to link them to each other is always to be understood as follows: in a first design variant of the subject matter of the invention, only the first feature may be present, in a second design variant only the second feature may be present, and in a third design variant both the first feature and the second feature may be present.

[0006] In addition, the term "about" used in this text gives a tolerance range that is regarded as common by a person skilled in the art. The term "about" should in particular be understood as a tolerance range of up to + / −20% of the relevant value, preferably up to + / −10% of the relevant value.

[0007] In addition, in the context of the present invention, relative concepts regarding features used in this text, such as "greater", "smaller", "higher", "lower", etc., are to be understood such that parametric deviations of the features in question that result from manufacturing and / or from implementation and that lie within the manufacturing / implementation tolerances of the corresponding manufacturing or implementation specifications of the features in question are not taken into account for the respective relative concepts. In other words, according to the definitions applicable in this text, the parameters of a feature are only regarded as "greater", "smaller", "higher", "lower", etc. than the parameters of a comparison feature in the context of the present invention if the two parameters being compared differ from each other so significantly in their values that their parametric difference definitely does not fall within the tolerance range of the feature in question caused by manufacturing / implementation but is the result of a purposeful action.

[0008] The present invention relates to an operating element having an operating area and a capacitive sensing device for detecting an approach to the operating area by an operator as an operating input and / or a touch of the operating area by the operator as an operating input. According to the invention, the capacitive sensing device has an electrode arranged on the side of the operating area facing away from the operator and a counter electrode also arranged on the side of the operating area facing away from the operator for generating a measurement capacitance associated with the capacitive operating area. The capacitive sensing device has an analysis unit that can be selectively electrically connected to the electrode for determining the electric potential applied to the electrode, respectively. Preferably, the analysis unit has an analog-to-digital converter for determining the measurement capacitance. Still more preferably, the analysis unit (including the analog-to-digital converter) is an integrated component of a microcontroller, and this component together with the electrode forming the measurement capacitance forms the capacitive sensing device. According to the invention, the capacitive sensing device is formed to implement a method having at least the following steps.

[0009] In a first step (which is also the first step of a sequence of multiple steps described below and together constituting a measurement cycle), the electrode is set to a predetermined initial potential, which is preferably less in absolute value than a first potential and a second potential described below and preferably corresponds to the ground potential in most cases.

[0010] In a second step following the first step, the electrode is charged, i.e., a charge is applied to the electrode, and at the same time the counter electrode is held at a first reference potential, which is less in absolute value than at least the potential ultimately applied to the electrode. Both the charging and the holding last for a predetermined first duration. The first reference potential preferably corresponds to the initial potential and preferably corresponds to the ground potential in most cases. In the sense of the present invention, "holding" preferably does not necessarily mean strictly maintaining a constant value, but in the sense of the present invention, "holding" can implicitly mean a relatively small change over time of the relevant potential compared to "charging", and "holding" preferably includes an average fluctuation over time of less than 10% during the step involved.

[0011] In a subsequent third step, an influencing potential different from the first reference potential, such as the operating voltage of the above-mentioned microcontroller, is applied to the counter electrode for a predetermined second duration, such that the influencing potential is greater in absolute value than the first reference potential of the first step and greater than at least the potential ultimately applied to the electrode.

[0012] In a fourth step within the second duration, the analysis unit is connected to the electrode that was previously insulated from the analysis unit at the latest before the end of the second duration, and a first potential is determined by means of the analysis unit connected to the electrode, which first potential is set by the influencing potential applied to the counter electrode at the end of the second duration.

[0013] In a subsequent fifth step, the electrode is again set to the predetermined initial potential, which is preferably less in absolute value than the first potential and a second potential described below and corresponds, for example, to the ground potential, while maintaining the application of the influencing potential to the counter electrode.

[0014] In a subsequent sixth step, the electrode is charged, i.e., a charge is applied to the electrode, and at the same time the counter electrode is held at the influencing potential. Both the charging and the holding last for a predetermined third duration.

[0015] In a subsequent seventh step, the first reference potential or a second reference potential different from the first reference potential is applied to the counter electrode for a predetermined fourth duration, and the second reference potential is less in absolute value than at least the potential ultimately applied to the electrode.

[0016] In an eighth step within a fourth duration, the analysis unit is connected to the electrode that was previously insulated from the analysis unit, at the latest before the end of the fourth duration, and a second electric potential is determined by the analysis unit connected to the electrode, the second electric potential being set by a first reference electric potential or a second reference electric potential applied to the counter electrode at the end of the fourth duration.

[0017] According to the invention, the above steps formed by the first step to the eighth step are repeatedly performed multiple times in the sequence of their numbers, where the sequences respectively form measurement cycles. According to the invention, after each measurement cycle, the change of the value formed by the first electric potential previously obtained in the fourth step and the second electric potential previously obtained in the eighth step with respect to the value (referred to as the old value) previously obtained in a previous, preferably directly previous measurement cycle is qualitatively and / or quantitatively acquired by the capacitive sensing device, so as to positively or negatively detect the touch or proximity to the operation area by means of the change and output a corresponding detection result by the capacitive sensing device.

[0018] The design of the operating element according to the invention has the following advantages: by determining the electrode electric potential twice (i.e., the first electric potential and the second electric potential) in one measurement cycle, and changing the counter electric potential of the counter electrode in the opposite polarity with respect to the electrode (i.e., once higher than the electric potential of the electrode and once lower than the electric potential of the electrode), the influence of temperature on the measured capacitance, such as caused by mechanical changes (such as expansion or position change) of the participating electrodes, is reduced or eliminated.

[0019] That is, it has been shown that although in any case the temperature influence is a change in the same direction of these electric potentials (i.e., the first electric potential and the second electric potential) determined at the electrode, the changes of these two electric potentials (i.e., the first electric potential and the second electric potential) determined in the fourth step and the eighth step due to the proximity and touch of the operation area are in the opposite direction. By substantially eliminating the influence of temperature on the measured capacitance, this leads to an improvement in the touch detection or proximity detection of the change in the value derived from the previously determined two electric potentials from the first electric potential and the second electric potential.

[0020] Preferably, the change of the obtained value with respect to the old value is compared with a pre-given comparison change to positively or negatively detect the touch or proximity to the operation area by means of the comparison.

[0021] Still more preferably, the smallest change of the value determined from one measurement cycle to the next measurement cycle that is less than the pre-given absolute value is used to subsequently fit the pre-given comparison change. This working method is called baseline fitting.

[0022] The numerical values are preferably the differences between the first electric potential and the second electric potential respectively, and a touch or proximity to the operating area is definitely detected only when exceeding a pre-given absolute minimum difference which is a pre-given contrast change.

[0023] The respectively predetermined durations formed by the first to fourth durations can be selected to be relatively short. For example, these durations can be a few microseconds, such as 1 μs to 2 μs or 0.5 μs to 10 μs, such as 5 μs. These durations can be, for example, respectively only a few clock cycles of the calculation and storage units used in the capacitive sensing device. The calculation and storage units or the microcontroller can operate, for example, at a clock frequency of 64 MHz, so that the durations formed by the first to fourth durations can also be in the range of a few nanoseconds or a few tens of nanoseconds or a few hundreds of nanoseconds. It should be understood that the shorter the corresponding durations are determined, the more measurement cycles can be achieved in each time interval. However, it is also conceivable to change the durations formed by the first to fourth durations from one measurement cycle to the next.

[0024] The first duration and the third duration are preferably selected to be the same respectively.

[0025] The second duration and the fourth duration are preferably selected to be the same respectively.

[0026] According to a preferred design, the first, second, third, and fourth durations are all selected to be the same.

[0027] The invention further relates to the use of the operating element according to one of the above-described embodiments in a motor vehicle.

[0028] The invention also relates to a method for detecting the proximity or contact of an operator to the operating area of an operating element, the method having the following steps:

[0029] In an initial providing step, an operating element having an operating area and a capacitive sensing device is provided. Here, the capacitive sensing device of the provided operating element has an electrode and a counter electrode for generating a measurement capacitance associated with the capacitive operating area on the side of the operating area facing away from the operator, and an analysis unit capable of selectively electrically connecting to the electrode.

[0030] In a first step (which is also the first step of a sequence of multiple steps described below and jointly constituting a measurement cycle), the electrode is set to a predetermined initial electric potential, and the initial electric potential is preferably smaller in absolute value than the first electric potential and the second electric potential described below and preferably corresponds to the ground electric potential in most cases.

[0031] In a second step following the first step, the electrode is charged, i.e., a charge is applied to the electrode, and at the same time the counter electrode is held at a first reference potential which is smaller in absolute value than at least the potential ultimately applied to the electrode. Both the charging and the holding last for a respective predetermined first duration. The first reference potential preferably corresponds to the initial potential and, in most cases, preferably corresponds to the ground potential. In the sense of the present invention, "holding" preferably does not necessarily mean strictly holding constant, but rather "holding" in the sense of the present invention can implicitly mean a smaller change over time of the relevant potential compared to "charging", and "holding" preferably includes an average fluctuation over time of less than 10% during the step involved.

[0032] In a subsequent third step, an influencing potential different from the first reference potential, such as the operating voltage of the above-mentioned microcontroller, is applied to the counter electrode for a predetermined second duration such that the influencing potential is greater in absolute value than the first reference potential of the first step and greater than at least the potential ultimately applied to the electrode.

[0033] In a fourth step within the second duration, and at the latest before the end of the second duration, the analysis unit is connected to the electrode which was previously insulated with respect to the analysis unit and a first potential is determined by means of the analysis unit connected to the electrode, the first potential being set by the influencing potential applied to the counter electrode at the end of the second duration.

[0034] In a subsequent fifth step, the electrode is again set to the predetermined initial potential which is preferably smaller in absolute value than the first potential and a second potential described below and which corresponds, for example, to the ground potential, while maintaining the application of the influencing potential to the counter electrode.

[0035] In a subsequent sixth step, the electrode is charged, i.e., a charge is applied to the electrode, and at the same time the counter electrode is held at the influencing potential. Both the charging and the holding last for a respective predetermined third duration.

[0036] In a subsequent seventh step, the first reference potential or a second reference potential different from the first reference potential is applied to the counter electrode for a predetermined fourth duration, the second reference potential being smaller in absolute value than at least the potential ultimately applied to the electrode.

[0037] In an eighth step within a fourth duration, the analysis unit is connected to the electrode that was previously insulated from the analysis unit, at the latest before the end of the fourth duration, and a second electric potential is determined by the analysis unit connected to the electrode, the second electric potential being set by a first reference electric potential or a second reference electric potential applied to the counter electrode as the fourth duration ends.

[0038] According to the invention, the above steps formed by the first step to the eighth step are repeated a plurality of times in the sequence of their numbers, where the sequences respectively form measurement cycles. According to the invention, after each measurement cycle, a change in a value formed by the first electric potential previously obtained in the fourth step and the second electric potential previously obtained in the eighth step with respect to an old value previously obtained in a previous, preferably directly preceding, measurement cycle is qualitatively and / or quantitatively acquired by the capacitive sensing device, so as to positively or negatively detect a touch or proximity to the operating area by means of the change and output a corresponding detection result by the capacitive sensing device.

[0039] The design of the method according to the invention has the following advantages: by determining the electrode electric potential twice (i.e., the first electric potential and the second electric potential) in one measurement cycle, and by changing the counter electric potential of the counter electrode with opposite polarities with respect to the electrode (i.e., once higher than the electric potential of the electrode and once lower than the electric potential of the electrode), the influence of temperature on the measurement capacitance, which is caused by, for example, mechanical changes (such as expansion or position change) of the participating electrodes and thus obtained from the measurement capacitance, is reduced or eliminated.

[0040] That is, it has been shown that although in any case the temperature influence is a change in the same direction of these electric potentials (i.e., the first electric potential and the second electric potential) determined at the electrode, the changes in these two electric potentials (i.e., the first electric potential and the second electric potential) determined in the fourth step and the eighth step due to proximity and touch to the operating area are in opposite directions. By substantially eliminating the influence of temperature on the measurement capacitance, this results in an improvement in touch detection or proximity detection of the change in the value derived from the previously determined two electric potentials from the first electric potential and the second electric potential.

[0041] Preferably, the change in the obtained value is compared with a pre-given contrast change to positively or negatively detect a touch or proximity to the operating area by means of the comparison.

[0042] Still more preferably, the smallest change in the value determined from one measurement cycle to the next measurement cycle that is less than the pre-given absolute value is used to subsequently fit the pre-given contrast change. This working mode is called baseline fitting.

[0043] The numerical values are preferably the differences between the first electric potential and the second electric potential, respectively, and a touch or proximity to the operating area is definitely detected only when exceeding a pre-given absolute minimum difference as a pre-given contrast change.

[0044] The respectively pre-given durations formed by the first to fourth durations can be selected to be relatively short. For example, these durations can be a few microseconds, such as 1 μs to 2 μs or 0.5 μs to 10 μs, such as 5 μs. These durations can, for example, each be only a few clock cycles of the calculation and storage units used in the capacitive sensing device. The calculation and storage units or microcontrollers can, for example, operate at a clock frequency of 64 MHz, such that the durations formed by the first to fourth durations can also be in the range of a few nanoseconds or a few tens of nanoseconds or a few hundreds of nanoseconds. It should be understood that the shorter the respective durations are determined, the more measurement cycles can be achieved in each time interval. However, it is also conceivable to change the durations formed by the first to fourth durations from one measurement cycle to the next.

[0045] The first duration and the third duration are preferably selected to be the same respectively.

[0046] The second duration and the fourth duration are preferably selected to be the same respectively.

[0047] According to a preferred design, the first, second, third, and fourth durations are all selected to be the same. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Other features and advantages of the present invention are derived from the following description, not limited to the embodiments of the present invention to be understood, and the present invention will be described in detail below with reference to the drawings. Schematically shown in the drawings:

[0049] Figure 1 Showing an embodiment of an operating element according to the present invention;

[0050] Figure 2 Showing a flowchart of an embodiment of a method or an operating element according to the present invention;

[0051] Figure 3 Showing for demonstrating Figure 1 the electric potential U 1 and U 2 determined at the electrodes of the temperature dependence of the graph,

[0052] Figure 4 Showing a flowchart regarding temperature changes and contact events to demonstrate its influence on the numerical value ΔU determined by the method of the present invention.

[0053] Parts that are functionally equivalent in different figures are always provided with the same reference signs, so that they are generally described only once. Detailed Description of the Invention

[0054] Figure 1 An embodiment of an operating element 1 for detecting a touch on and / or an approach to an operating area 2 is shown. The operating area 2 is formed, for example, by a panel which covers the electrode S and the counter electrode S' from the perspective of the operator.

[0055] For the detection, the operating element 1 has a capacitive sensing device 3 which has an electrode S arranged on the side of the operating area 2 facing away from the operator and a counter electrode S' also arranged on the side of the operating area 2 facing away from the operator. These two electrodes S and S' are provided for generating a measurement capacitance associated with the capacitive operating area. The electrode S and the counter electrode S' are electrically insulated from each other and extend side by side, for example, in a meandering or fork-shaped manner respectively, wherein the electrode S and the counter electrode S' are arranged intertwined such that the gaps of one are filled by the other.

[0056] The capacitive sensing device 3 has an analysis unit μC in the form of a microcontroller here. The analysis unit can be selectively electrically connected to the electrode S in particular for determining the electric potential applied to the electrode S respectively. In addition, the analysis unit μC is also connected to the counter electrode S', is also fed with a supply potential Vcc, and has a connection to the ground potential. The analysis unit μC is also formed to set the initial potential GND of the electrode S and to charge it and selectively set a first reference potential GND' or optionally a second reference potential GND” and the influence potential Vcc of the counter electrode S'.

[0057] The sensing device 3 is formed to perform the reference Figure 2 subsequent steps described below. Figure 2 The time-dependent potential curve U(t) of the electrode S and the time-dependent potential curve of the counter electrode S' (also referred to as the counter potential U'(t)) during a measurement cycle formed by the steps i to viii described below are shown here, wherein the situation shown is that no touch or approach of the operator occurs during the measurement cycle.

[0058] In a first step i (which is also the first step of a sequence of steps ii to viii described below and together form a measurement cycle), the electrode S is set to a predetermined initial potential GND, which initial potential is preferably smaller in absolute value than the first potential U 1 and the second potential U 2 described below and preferably corresponds to the ground potential in most cases.

[0059] At the time point t after the first step i 0Starting at time point t 1 In a second step ii that starts and ends at time point t, the electrode S is charged, i.e., a charge is applied to the electrode S, and at the same time the counter electrode S' is held at a first reference potential GND', which is less in absolute value than at least the potential that is ultimately (i.e., at the end time point t of the second step 1 ) applied to the electrode S. Both the charging and the holding last for a predetermined first duration respectively. The first reference potential GND' preferably corresponds to the initial potential GND of the electrode S and most preferably corresponds to the ground potential in most cases. In the sense of the present invention, "holding" preferably does not necessarily mean strictly maintaining a constant value, but in the sense of the present invention, "holding" can implicitly mean a relatively small change over time of the relevant potential compared to "charging", and "holding" preferably includes an average fluctuation over time of less than 10% during the step involved.

[0060] At time point t 1 In a third step iii following the second step ii, an influencing potential VCC (e.g., the operating voltage of the microcontroller of the analysis unit μC as previously described) different from the first reference potential GND' is applied to the counter electrode S' for a predetermined second duration Δt 2 , such that the influencing potential Vcc is greater in absolute value than the first reference potential GND' of the first step and greater than at least the potential U(t 2 ) applied to the electrode S at the end of this third step at time point t 2 ).

[0061] During the second duration Δt 2 or at the latest before the end of the second duration, in a fourth step iv, the analysis unit μC that was previously insulated from the electrode S is connected thereto.

[0062] At the latest with the end of the second duration Δt 2 (i.e., at time point t 2 ), also in the fourth step iv, a first potential U 1 is determined by means of the analysis unit μC connected to the electrode S, and the first potential is set on the electrode S by the influencing potential Vcc applied to the counter electrode S'.

[0063] In a subsequent fifth step v that starts at time point t 2 and ends at time point t 3 , the electrode S is again set to a predetermined initial potential GND, which is preferably less in absolute value than the first potential U 1 and the second potential U 2 described below and, for example, corresponds to the ground potential, while maintaining the application of the influencing potential Vcc to the counter electrode S'.

[0064] In a subsequent sixth step vi that starts at time point t 3 and ends at time point t 4 the electrode S is charged, i.e., a charge is applied to the electrode S, and at the same time the counter electrode S' is held at the influencing potential Vcc. The charging and holding each last for a predetermined third duration Δt 3 .

[0065] In a subsequent seventh step vii that starts at time point t 4 and ends at time point t 5 a first reference potential GND' or a second reference potential GND” different from the first reference potential GND' is applied to the counter electrode S' for a predetermined fourth duration Δt 4 , where the second reference potential is smaller in absolute value than at least the potential U(t 5 ) finally applied to the electrode S in the seventh step vii.

[0066] During the fourth duration Δt 4 or at the latest before the end of the fourth duration, in an eighth step viii the analysis unit μC is connected to the electrode S that was previously insulated with respect to the analysis unit μC. At the latest with the end of the fourth duration Δt 4 , i.e., at time point t 5 , a second potential U 2 is also determined by the analysis unit μC connected to the electrode S, where the second potential is set by the first reference potential GND' or the second reference potential GND” applied to the counter electrode S'.

[0067] Here, the above steps formed by the first step i to the eighth step viii are repeated several times in the sequence of their numbers, where the sequences each form a measurement cycle. After each measurement cycle, the change of the value ΔU formed by the first potential U 1 previously obtained in the fourth step iv and the second potential U 2 previously obtained in the eighth step viii with respect to a value (here called the old value) previously obtained in a previous, preferably directly preceding measurement cycle is qualitatively and / or quantitatively acquired by the capacitive sensing device 3. In order to positively or negatively detect a touch or proximity to the operating area 2 by means of the change of the value ΔU with respect to the old value and output a corresponding detection result by the capacitive sensing device 3. In the current design, the value ΔU is respectively the difference between the first potential U 1 and the second potential U 2 , where a touch or proximity to the operating area 2 is positively detected only when exceeding a predetermined minimum difference in absolute value as a predetermined comparison change.

[0068] The design of the operating element 1 according to the invention has the following advantages: By determining the electrode potential twice in one measurement cycle (i.e., the first potential U 1 and the second potential U 2 ), by changing the counter potential U'(t) applied to the counter electrode S' in opposite polarities with respect to the electrode S (i.e., once influencing the potential Vcc and once the first reference potential GND' or the second reference potential GND”), the influence of temperature on the measurement capacitance, which is caused, for example, by mechanical changes (such as expansion or position changes) of the participating electrodes and thus results from the measurement capacitance, is reduced or eliminated. That is, it has been shown that although the temperature influence is in the same direction of change of these potentials (i.e., the first potential U 1 and the second potential U 2 ) determined at the electrode S in any case, the changes of these two potentials (i.e., the first potential U 1 and the second potential U 2 ) determined in the fourth and eighth steps due to approaching and touching the operating area 2 are in the reverse direction. By substantially eliminating the influence of temperature on the measurement capacitance, this leads to an improvement in touch detection or proximity detection of the value ΔU derived from these two previously determined potentials from the first potential U 1 and the second potential U 2 .

[0069] Then, Figure 3 shows the first potential U 1 and the second potential U 2 determined at the electrode S, where it is simply assumed that there is a linear proportionality, and T 2 >T 1 .

[0070] In contrast, Figure 4 shows these two potentials determined at the electrode S (i.e., the first potential U 1 determined in the fourth step iv and the second potential U 2 determined in the eighth step viii) and the above-mentioned value ΔU derived therefrom, which is obtained here by the difference between the two (on the one hand, when touching B in the time interval t 6 <t<t 8 compared to not touching in the time intervals t<t 6 and t>t 8 , which are respectively marked by crossed-out B in Figure 4 ). Corresponding to Figure 3 , since the time point t 7 , the temperature starts to rise from T 1 and finally reaches T 2 long after the time point t8. It is shown that in the time interval t<t6 and t>t 8 in the case of no touch, the first potential U 1 (T 1 ) increases to the final U 1 (T 2 ), and the second potential U 2 undergoes a change in the same direction and here approximately the same in absolute value, i.e., also from U 2 (T 1 ) increases to the final U 2 (T 2 ), so that the no-touch situation can still be recognized essentially independently of the temperature change by means of the value ΔU. For the case of a touch in the time interval t 6 <t<t 8 , due to the dielectric influence of the operator's finger, an influence on the measured capacitance is generated, and due to different "polarizations" of the potential U', a reverse change of the first potential U1 and the second potential U2 caused by proximity or touch compared to the no-touch situation occurs, i.e., a decrease from U 1 (T 1 ) to U * 1 (T 1 ) (where the asterisk represents the touch or proximity situation) and an increase from U 2 (T 1 ) to U * 2 (T 1 ). The value ΔU of the touch and proximity situations * differs from the ΔU of the no-touch situation not only in the reverse change but also remains essentially unaffected by the temperature increase, as shown by the further temporal change of ΔU * up to the time point t 8 .

Claims

1. An operating element (1), comprising an operating area (2) and a capacitive sensor device (3) for detecting an operator approaching and / or touching the operating area (2), wherein the capacitive sensor device (3) comprises, on a side of the operating area (2) facing away from the operator, an electrode (S) and a counter electrode (S') for generating a measurement capacitance associated with the capacitive operating area, and an evaluation unit (μC) which can be selectively electrically connected to the electrode (S), wherein the capacitive sensor device (3) is formed to implement a method having at least the following steps: i. setting the electrode (S) to a predetermined initial potential (GND); ii. subsequently charging the electrode (S) and simultaneously maintaining the counter electrode (S') at a first reference potential (GND') for a predetermined first duration (Δt1), the first reference potential being smaller in absolute value than at least the potential finally applied to the electrode (S); iii. subsequently applying an influencing potential (Vcc) different from the first reference potential (GND') to the counter electrode (S') for a predetermined second duration (Δt2), such that the influencing potential (Vcc) is greater in absolute value than the first reference potential (GND') and greater than at least the potential finally applied to the electrode (S); iv. connecting the analysis unit (μC) to the electrode (S) at the latest before the end of the second duration (Δt2) and determining a first potential (U1) by means of the analysis unit (μC) connected to the electrode (S), the first potential being set by the influencing potential (Vcc) applied to the counter electrode (S') at the end of the second duration (Δt2); v. then setting the electrode (S) to the predetermined initial potential (GND) while maintaining the influencing potential (Vcc) applied to the counter electrode (S'); vi. subsequently charging said electrode (S) and simultaneously maintaining said counter electrode (S') at said influencing potential (Vcc), respectively for a predetermined third duration (Δt3), vii. subsequently applying the first reference potential (GND') or a second reference potential (GND") different from the first reference potential (GND') to the counter electrode (S') for a predetermined fourth duration (Δt4), the second reference potential being smaller in absolute value than the potential finally applied to at least the electrode (S); viii. connecting the analysis unit (μC) to the electrode (S) at the latest before the end of the fourth time period (Δt4) and determining a second potential (U2) by the analysis unit (μC), wherein the second potential (U2) is set by the first reference potential (GND') or the second reference potential applied to the counter electrode (S') at the end of the fourth time period (Δt4); Steps i to viii are repeated multiple times in sequence, wherein the steps respectively form a measurement cycle and after each measurement cycle, the capacitive sensing device (3) qualitatively and / or quantitatively acquires a change in a value (ΔU) formed by the first potential (U1) and the second potential (U2) relative to an old value previously acquired in a previous, preferably directly preceding, measurement cycle, so that the capacitive sensing device (3) detects a touch or approach to the operating area (2) positively or negatively by means of the change in the value (ΔU) relative to the old value and outputs a corresponding detection result.

2. An operating element (1) according to the preceding claim, wherein the capacitive sensor device (3) is formed to compare the change of the acquired numerical value (ΔU) relative to the old numerical value with a predetermined comparison change, so as to detect a touch on the operating area (2) or an approach to the operating area (2) positively or negatively by means of the comparison. 3 . The operating element ( 1 ) according to claim 1 , wherein a minimum change of the value (ΔU) between measuring cycles which is less than a predefined absolute value is used for subsequent adaptation to the predefined comparative change.

4. An operating element (1) according to one of the preceding claims, wherein the numerical value (ΔU) is the difference between a first potential (U1) and a second potential (U2), and a touch or approach to the operating area (2) is detected with certainty only when a predetermined absolute minimum difference as a predetermined contrast change is exceeded. 5 . The operating element ( 1 ) according to claim 1 , wherein the evaluation unit (μC) has an analog-to-digital converter (ADC) which is selectively connected to the electrode (S). 6 . The operating element ( 1 ) according to claim 1 , wherein the initial potential (GND) and the first reference potential (GND′) correspond to ground potential.

7. The operating element (1) according to one of the preceding claims, wherein the first duration (Δt1) and the third duration (Δt3) are each selected to be identical and / or the second duration (Δt2) and the fourth duration (Δt4) are each selected to be identical.

8. Use of an operating element (1) according to one of the preceding claims in a motor vehicle.

9. A method for detecting an operator's approach to and / or contact with an operating area (2) of an operating element (1), the method comprising an initial provision step, in which the operating element (1) having the operating area (2) and a capacitive sensor device (3) is provided, and wherein the capacitive sensor device (3) has, on a side of the operating area (2) facing away from the operator, an electrode (S) and a counter electrode (S') for generating a measurement capacitance associated with the capacitive operating area, and an evaluation unit (μC) which can be selectively electrically connected to the electrode (S); the method further comprising the following steps: i. setting the electrode (S) to a predetermined initial potential (GND); ii. subsequently charging the electrode (S) and simultaneously maintaining the counter electrode (S') at a first reference potential (GND') for a predetermined first duration (Δt1), the first reference potential being smaller in absolute value than at least the potential finally applied to the electrode (S); iii. subsequently applying an influencing potential (Vcc) different from the first reference potential (GND') to the counter electrode (S') for a predetermined second duration (Δt2), such that the influencing potential (Vcc) is greater in absolute value than the first reference potential (GND') and greater than at least the potential finally applied to the electrode (S); iv. connecting the analysis unit (μC) to the electrode (S) at the latest before the end of the second duration (Δt2) and determining a first potential (U1) by means of the analysis unit (μC) connected to the electrode (S), the first potential being set by the influencing potential (Vcc) applied to the counter electrode (S') at the end of the second duration (Δt2); v. then setting the electrode (S) to the predetermined initial potential (GND) while maintaining the influencing potential (Vcc) applied to the counter electrode (S'); vi. subsequently charging said electrode (S) and simultaneously maintaining said counter electrode (S') at said influencing potential (Vcc), respectively for a predetermined third duration (Δt3), vii. subsequently applying the first reference potential (GND') or a second reference potential (GND") different from the first reference potential (GND') to the counter electrode (S') for a predetermined fourth duration (Δt4), the second reference potential being smaller in absolute value than the potential finally applied to at least the electrode (S); viii. connecting the analysis unit (μC) to the electrode (S) at the latest before the end of the fourth time period (Δt4) and determining a second potential (U2) by the analysis unit (μC), the second potential being set by the first reference potential (GND') or the second reference potential applied to the counter electrode (S') at the end of the fourth time period (Δt4); Steps i to viii are repeated multiple times in sequence, wherein these steps respectively form a measurement cycle and after each measurement cycle, the capacitive sensor device (3) qualitatively and / or quantitatively acquires a change in a value (ΔU) formed by the first potential (U1) and the second potential (U2) relative to an old value previously acquired in a previous, preferably directly preceding, measurement cycle, so that the capacitive sensor device (3) can detect a touch or approach to the capacitive operating area (2) positively or negatively based on the change and output a corresponding detection result through the capacitive sensor device (3).

10. A method according to the preceding claim, wherein the capacitive sensing device (3) is formed to compare the change of the acquired value (ΔU) relative to the old value with a predetermined comparison change, so as to detect a touch on the operating area (2) or an approach to the operating area (2) positively or negatively by means of the comparison. 11 . The method according to claim 1 , wherein a minimum change of the value (ΔU) between measuring cycles which is less than a predefined absolute value is used for subsequent fitting of the predefined comparative change.

12. A method according to any of the preceding claims 9 to 11, wherein the numerical value (ΔU) is the difference between a first potential (U1) and a second potential (U2), and a touch on the operating area (2) or an approach to the operating area (2) is detected with certainty only when a predetermined absolute minimum difference as a predetermined contrast change is exceeded. 13 . The method according to claim 9 , wherein the evaluation unit (μC) has an analog-to-digital converter (ADC) for selective connection to the electrode (S). 14 . The method according to claim 9 , wherein the initial potential (GND) and the first reference potential (GND′) correspond to ground potential.

15. The method according to claim 9, wherein the first duration (Δt1) and the third duration (Δt3) are each selected to be identical and / or the second duration (Δt2) and the fourth duration (Δt4) are each selected to be identical.

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