Control element with capacitive sensor technology for detecting proximity and / or touch with improved reduction of temperature influence, its use and associated detection method

Abstract

Control element (1) with control panel (2) and capacitive sensor (3) for detecting an approach and / or touch of the control panel (2) by an operator, wherein the capacitive sensor (3) has on a side of the control panel (2) facing away from the operator an electrode (S) and a counter electrode (S') for generating a measuring capacitance associated with the capacitive control panel and an evaluation unit (µC) that can be selectively electrically connected to the electrode (S), wherein the capacitive sensor (3) is configured to perform a method comprising at least the following steps: i. Setting the electrode (S) to a predetermined initial electrical potential (GND); ii. subsequent charging of the electrode (S) and simultaneous holding of the counter electrode (S') at a first ground potential (GND') which is in magnitude less than the potential applied at the electrode (S) at least at the end, each for a predetermined first time period (Δt1); iii. subsequent application of an influencing potential (Vcc) to the counter electrode (S') that differs from the first basic potential (GND') such that the influencing potential (Vcc) is greater in magnitude than the first basic potential (GND') and the potential applied at least finally to the electrode (S) for a predetermined second time period (Δt2); iv. at the latest before the end of the second time period (Δt2) connect the evaluation unit (µC) to the electrode (S) and determine an electrical first potential (U1) that arises at the electrode (S) due to the influencing potential (Vcc) applied to the counter electrode (S') after the second time period (Δt2) by the evaluation unit (µC) connected to the electrode (S); v. subsequent adjustment of the electrode (S) to the predetermined initial electrical potential (GND) while maintaining the application of the influencing potential (Vcc) to the counter electrode (S'); vi. subsequent charging of the electrode (S) and simultaneous holding of the counter electrode (S') at the influencing potential (Vcc) each for a predetermined third time period (Δt3), vii. subsequent application of the first basic potential (GND') or a second basic potential (GND") that differs from the first basic potential (GND') and is lower in magnitude than the potential applied at least at the end of the electrode (S) for a predetermined fourth time period (Δt4); viii. at the latest before the expiry of the fourth time period (Δt4) connect the evaluation unit (µC) to the electrode (S) and determine a second electrical potential (U2) that arises at the electrode (S) due to the first basic potential (GND') or second basic potential applied to the counter electrode (S') after the expiry of the fourth time period (Δt4) by the evaluation unit (µC); Repeating steps i to viii multiple times in sequence, each forming a measurement cycle, and after each measurement cycle qualitatively and / or quantitatively determining a change in a quantity (ΔU) formed from the first potential (U1) and from the second potential (U2) compared to a previous quantity determined in a preceding, preferably the immediately preceding, measurement cycle by means of the capacitive sensor (3), in order to detect the touching or approaching the control panel (2) positively or negatively by means of the capacitive sensor (3) based on a change in the quantity (ΔU) compared to the previous quantity and to output a corresponding detection result by means of the capacitive sensor (3).

Description

[0001] The present invention relates to a control element with capacitive sensors for detecting approach and / or touch with improved temperature influence reduction, its use, and an associated detection method. Touch-sensitive control panels are very popular for detecting user input. Capacitive sensors are preferably used for touch detection because their sensitivity is comparatively high and reliable. These capacitive sensors, assigned to the respective control panel, generally comprise at least one electrode and an associated evaluation unit. Conventional capacitive sensors incorporate expensive, specialized hardware components such as tilting oscillators and comparators. A sensor that does not use such components is known, for example, from US 8,836,350 B2.Besides electromagnetic interference, a problem affecting capacitive sensors but one that is relatively easy to manage, another issue arises in practice due to the sensors' temperature sensitivity. Particularly in motor vehicles, capacitive sensors are exposed to large temperature fluctuations, which leads to significant variations in the measuring capacitance assigned to the control panels. This can result in false detections due to supposed user input, a phenomenon known as "ghost touch." For manufacturing reasons and to simplify electrical contacting, such measuring capacitances are implemented using metallic coatings on a foil substrate, forming one or more electrodes. These coatings are typically located on the side of a sensor facing away from the user. Temperature-related changes in expansion and position cannot be completely suppressed mechanically.Therefore, it is necessary to neutralize the change in measuring capacity caused by the temperature change, which is also referred to here as temperature compensation.

[0002] DE 10 2020 102 249 A1 discloses an operating element with a control panel and capacitive sensors for detecting an approach to and / or touch of the control panel by an operator, wherein the capacitive sensors have an electrode and a counter electrode on a side of the control panel facing away from the operator for generating a measuring capacitance associated with the capacitive control panel and an evaluation unit that can be selectively electrically connected to the electrode. The capacitive sensors perform the following steps: i. Setting the electrode to a predetermined initial electrical potential; ii. subsequent charging of the electrode and simultaneous holding of the counter electrode at a first basic potential, which is in magnitude lower than the potential at least finally applied to the electrode; iii. Subsequent application of an influencing potential to the counter electrode that differs from the first basic potential, such that the influencing potential is greater in magnitude than the first basic potential.

[0003] DE 10 2012 105 266 A1 also discloses a capacitive proximity sensor for a motor vehicle, wherein the electrodes can be switched to ground or Uo by means of a switch. A generic method for capacitive touch and actuation detection is known from DE 10 2020 110 172 A1.

[0004] Against this background, the present invention aims to provide a control element with capacitive sensors for detecting approach or touch, which, in addition to precise detection, ensures a minimization of the temperature influence on detection, is particularly cost-effective, and exhibits low complexity. This objective is achieved by a control element with the features of claim 1 and by a method with the features of the dependent claim. Further, particularly advantageous embodiments of the invention are disclosed in the respective dependent claims.

[0005] It should be noted that the features listed individually in the following description can be combined in any technically sensible way and demonstrate further embodiments of the invention. The description further characterizes and specifies the invention, particularly in conjunction with the figures.

[0006] It should also be noted that the conjunction “and / or” used below, which stands between two features and links them together, is always to be interpreted in such a way that in a first embodiment of the object according to the invention only the first feature may be present, in a second embodiment only the second feature may be present, and in a third embodiment both the first and the second feature may be present.

[0007] Furthermore, the term "approximately" used herein indicates a tolerance range that a person skilled in the art in this field would consider customary. In particular, the term "approximately" is to be understood as a tolerance range of the relative quantity of up to a maximum of + / -20%, preferably up to a maximum of + / -10%.

[0008] Furthermore, relative terms used herein with respect to a feature, such as “larger”, “smaller”, “higher”, “lower” and the like, are always to be interpreted in such a way that manufacturing and / or implementation-related size deviations of the feature in question, which are within the manufacturing / implementation tolerances defined for the respective manufacturing or implementation of the feature in question, are not covered by the respective relative term.In other words, according to the definition applicable herein, a size of a feature is to be regarded as "larger", "smaller", "higher", "lower" and the like within the meaning of the present invention than a size of a comparison feature only if the two sizes compared differ so significantly in their value that this difference in size certainly does not fall within the manufacturing / implementation-related tolerance range of the feature in question, but is the result of deliberate action.

[0009] The invention relates to a control element with a control panel and capacitive sensors for detecting an approach to the control panel by the operator as an input and / or a touch of the control panel by the operator, also as an input. According to the invention, the capacitive sensor has an electrode arranged on a side of the control panel facing away from the operator and a counter electrode also arranged on the same side of the control panel to generate a measuring capacitance associated with the capacitive control panel. The capacitive sensor has an evaluation unit that can be selectively electrically connected to the electrode for determining the potential applied to the electrode. Preferably, the evaluation unit has an analog-to-digital converter for determining the measuring capacitance.Even more preferably, the evaluation unit, including the analog-to-digital converter, is an integrated component of a microcontroller, which, together with the electrodes forming the measuring capacitance, constitutes the capacitive sensor. According to the invention, the capacitive sensor is configured to execute a method comprising at least the following steps.

[0010] In a first step, which is the first step of a sequence that is further comprised of several steps described below and which together form a measurement cycle, the electrode is set to a predetermined initial electrical potential, which is preferably lower in magnitude than the first and second potentials described below and usually preferably corresponds to the ground potential.

[0011] In a second step following the first, the electrode is charged, i.e., an electrical charge is applied to the electrode, and simultaneously the counter electrode is held at a first base potential, which is lower in magnitude than the potential applied at least at the end of the process at the electrode. Both the charging and holding processes take place for a predetermined initial duration. Preferably, the first base potential corresponds to the initial potential, and more preferably, it corresponds to the ground potential. "Holding" in the sense of the invention preferably, but not necessarily, means maintaining a strictly constant potential. Rather, "holding" in the sense of the invention can imply a smaller temporal variation of the potential compared to "charging." Preferably, "holding" involves an average temporal fluctuation of less than 10% over the respective step.

[0012] In a subsequent third step, the counter electrode is subjected to an influencing potential that differs from the first basic potential, for example the operating voltage of the previously described microcontroller, such that the influencing potential is greater in magnitude than the first basic potential of the first step and the potential at least finally applied to the electrode for a predetermined, second period of time.

[0013] In a fourth step, which lies within the second time period, the evaluation unit is connected to the electrode, which was previously isolated from the evaluation unit, at the latest before the end of the second time period, and an electrical first potential, which arises at the electrode due to the influencing potential applied to the counter electrode at the end of the second time period, is determined by means of the evaluation unit connected to the electrode.

[0014] In a subsequent fifth step, the electrode is again adjusted to the predetermined initial electrical potential, which is preferably lower in magnitude than the first potential and the second potential described below, and corresponds, for example, to the ground potential, while the application of the influencing potential to the counter electrode is maintained.

[0015] In a subsequent sixth step, the electrode is charged, i.e., an electrical charge is applied to the electrode and the counter electrode is simultaneously held at the influencing potential, i.e., charging and holding, for a predetermined third period of time.

[0016] In the subsequent seventh step, the counter electrode is subjected to the first basic potential or a second basic potential that differs from the first basic potential and is lower in magnitude than the potential that is at least finally applied to the electrode for a predetermined fourth period of time.

[0017] In an eighth step, which lies within the fourth time period, the evaluation unit is connected to the electrode, which was previously isolated from the evaluation unit, at the latest before the end of the fourth time period, and an electrical second potential is determined by the evaluation unit connected to the electrode, which arises at the electrode due to the first or second basic potential applied to the counter electrode at the end of the fourth time period.

[0018] According to the invention, the aforementioned steps from the first to the eighth step are repeated multiple times in the sequence of their numbering, each of these sequences constituting a measurement cycle. According to the invention, after each measurement cycle, a change in a quantity derived from the first potential determined in the fourth step and the second potential determined in the eighth step, compared to a quantity determined in a previous measurement cycle (preferably the immediately preceding one), is qualitatively and / or quantitatively determined by the capacitive sensor. This change is used to detect, positively or negatively, contact with or approach to the control panel by the capacitive sensor and to output a corresponding detection result.

[0019] The design of the control element according to the invention has the advantage that temperature influences on the measuring capacity, which result, for example, from mechanical changes of the electrodes involved, such as expansion or change in position, can be reduced or eliminated by determining the electrode potential twice, namely the first and second potential, in one measuring cycle, but with the counter-potential of the counter-electrode being reversed in terms of polarity with respect to the electrode, namely once above the potential of the electrode and once below the potential of the electrode.

[0020] It has been shown that while the temperature influence at most results in a change in the same direction in the potentials determined at the electrode, namely the first potential and the second potential, the change in the two potentials determined in the fourth and eighth steps, namely the first potential and the second potential, caused by approaching and touching the control panel, is in the opposite direction. This leads to the change in the quantity derived from the two previously determined potentials of the first and second potential improving the touch or proximity detection by largely eliminating the temperature influence on the measuring capacitance.

[0021] Preferably, the determined change in size compared to the original size is compared with a predetermined reference change in order to detect positive or negative contact or approach to the control panel based on the comparison.

[0022] Even more preferred is the use of a minimal change in the quantity, below a predetermined amount, detected from one measurement cycle to the next, for the subsequent adjustment of the predetermined comparison change. This procedure is known as baseline adjustment.

[0023] Preferably, the magnitude is a difference between the first potential and the second potential, whereby a touch or approach to the control panel is positively detected only when a predetermined minimum absolute difference is undershot as a predetermined change in comparison.

[0024] The predetermined duration of each of the first four time intervals can be relatively short. For example, it can be a few microseconds, e.g., 1 µs to 2 µs, or 0.5 µs to 10 µs, e.g., 5 µs. It can also be just a few clock cycles of the processing and storage unit used in the capacitive sensor. For example, the processing and storage unit or microcontroller can operate at a clock frequency of 64 MHz, so the duration of each of the first four time intervals can also be in the range of a few nanoseconds, a few tens of nanoseconds, or a few hundred nanoseconds. It goes without saying that the shorter the respective durations are, the more measurement cycles can be achieved per time interval. It is also conceivable to vary at least one of the durations from the first to the fourth time intervals from one measurement cycle to the next.Preferably, the first and third time periods are chosen to be identical.

[0025] Preferably, the second and fourth time periods are chosen to be identical.

[0026] According to a preferred embodiment, all time periods, the first, second, third and fourth, are chosen identically.

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

[0028] The invention further relates to a method for detecting an approach to or touch of a control panel of a control element by an operator, comprising the following steps: In an initial deployment step, the control element with the control panel and capacitive sensor is deployed. The capacitive sensor of the deployed control element has an electrode and a counter electrode on the side of the control panel facing away from the operator, for generating a measuring capacitance associated with the capacitive control panel, and an evaluation unit that can be selectively electrically connected to the electrode.

[0029] In a first step, which is the first step of a sequence that further consists of several steps described below and which together form a measurement cycle, the electrode is set to a predetermined initial electrical potential, which is preferably lower in magnitude than the first and second potentials described below and usually preferably corresponds to the ground potential.

[0030] In a second step following the first, the electrode is charged, i.e., an electrical charge is applied to the electrode, and simultaneously the counter electrode is held at a first base potential, which is lower in magnitude than the potential applied at least at the end of the process at the electrode. Both charging and holding are performed for a predetermined initial time period. Preferably, the first base potential corresponds to the initial potential, and more preferably, it corresponds to the ground potential. "Holding" in the sense of the invention preferably, but not necessarily, means maintaining a strictly constant potential; rather, "holding" in the sense of the invention can imply a smaller temporal variation of the potential compared to "charging." Preferably, "holding" involves an average temporal fluctuation of less than 10% over the respective step.

[0031] In a subsequent third step, the counter electrode is subjected to an influencing potential that differs from the first basic potential, for example the operating voltage of the previously described microcontroller, such that the influencing potential is greater in magnitude than the first basic potential of the first step and the potential at least finally applied to the electrode for a predetermined, second period of time.

[0032] In a fourth step, which lies within the second time period, the evaluation unit is connected to the electrode, which was previously isolated from the evaluation unit, at the latest before the end of the second time period, and an electrical first potential, which arises at the electrode due to the influencing potential applied to the counter electrode at the end of the second time period, is determined by means of the evaluation unit connected to the electrode.

[0033] In a subsequent fifth step, the electrode is again adjusted to the predetermined initial electrical potential, which is preferably lower in magnitude than the first potential and the second potential described below, and corresponds, for example, to the ground potential, while the application of the influencing potential to the counter electrode is maintained.

[0034] In a subsequent sixth step, the electrode is charged, i.e., an electrical charge is applied to the electrode and the counter electrode is simultaneously held at the influencing potential, i.e., charging and holding, for a predetermined third period of time.

[0035] In the subsequent seventh step, the counter electrode is subjected to the first basic potential or a second basic potential that differs from the first basic potential and is lower in magnitude than the potential that is at least finally applied to the electrode for a predetermined fourth period of time.

[0036] In an eighth step, which lies within the fourth time period, the evaluation unit is connected to the electrode, which was previously isolated from the evaluation unit, at the latest before the end of the fourth time period, and an electrical second potential is determined by the evaluation unit connected to the electrode, which arises at the electrode due to the first or second basic potential applied to the counter electrode at the end of the fourth time period.

[0037] According to the invention, the aforementioned steps from the first to the eighth step are repeated multiple times in the sequence of their numbering, each of these sequences constituting a measurement cycle. According to the invention, after each measurement cycle, a change in a quantity derived from the first potential determined in the fourth step and the second potential determined in the eighth step is qualitatively and / or quantitatively determined by the capacitive sensor compared to a previous, preferably the immediately preceding, measurement cycle. This change is then used to detect, positively or negatively, touching or approaching the control panel by the capacitive sensor and to output a corresponding detection result.

[0038] The inventive design of the method has the advantage that temperature influences on the measuring capacity, which result, for example, from mechanical changes in the electrodes involved, such as expansion or change in position, and thus on the measuring capacity, can be reduced or eliminated by determining the electrode potential twice, namely the first and second potential, in one measuring cycle, but with the counter-potential of the counter-electrode being reversed in opposite directions with respect to the electrode, namely once above the potential of the electrode and once below the potential of the electrode.

[0039] It has been shown that while the temperature influence at most results in a change in the same direction in the potentials determined at the electrode, namely the first potential and the second potential, the change in the two potentials determined in the fourth and eighth steps, namely the first potential and the second potential, caused by approaching and touching the control panel, is in the opposite direction. This leads to the change in the quantity derived from the two previously determined potentials of the first and second potential improving the touch or proximity detection by largely eliminating the temperature influence on the measuring capacitance.

[0040] Preferably, the determined change in size is compared with a predetermined reference change in order to detect, based on the comparison, whether the touching or approaching the control panel is positive or negative.

[0041] Even more preferred is the use of a minimal change in the quantity, below a predetermined amount, detected from one measurement cycle to the next, for the subsequent adjustment of the predetermined comparison change. This procedure is known as baseline adjustment.

[0042] Preferably, the magnitude is a difference between the first potential and the second potential, whereby a touch or approach to the control panel is positively detected only when a predetermined minimum absolute difference is undershot as a predetermined change in comparison.

[0043] The predetermined duration of each of the first four time intervals can be relatively short. For example, it can be a few microseconds, e.g., 1 µs to 2 µs, or 0.5 µs to 10 µs, e.g., 5 µs. It can also be just a few clock cycles of the processing and storage unit used in the capacitive sensor. For example, the processing and storage unit or microcontroller can operate at a clock frequency of 64 MHz, so the duration of each of the first four time intervals can also be in the range of a few nanoseconds, a few tens of nanoseconds, or a few hundred nanoseconds. It goes without saying that the shorter the respective durations are, the more measurement cycles can be achieved per time interval. It is also conceivable to vary at least one of the durations from the first to the fourth time intervals from one measurement cycle to the next.

[0044] Preferably, the first and third time periods are chosen to be identical.

[0045] Preferably, the second and fourth time periods are chosen to be identical.

[0046] According to a preferred embodiment, all time periods, the first, second, third and fourth, are chosen identically.

[0047] Further features and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention, which are not to be understood as limiting and are explained in more detail below with reference to the figures. These figures schematically show: Fig. 1 an embodiment of a control element according to the invention; Fig. 2 a flowchart of an embodiment of the method or control element according to the invention; Fig. 3 a diagram to illustrate the temperature dependence of the electrode Fig. 1 specific potentials U1 and U2, Fig. 4 a flowchart with temperature change and a contact event to illustrate their effect on the quantity ΔU determined by the method according to the invention.

[0048] In the different figures, parts that are equivalent in function are always provided with the same reference symbols, so that they are usually only described once.

[0049] Fig. Figure 1 represents an embodiment of a control element 1 for detecting a touch of a control panel 2 and / or approach to the control panel 2.

[0050] The control panel 2 is formed, for example, by a cover that covers the electrode S and counter electrode S' from the operator's point of view.

[0051] For detection, the control element 1 has a capacitive sensor 3, an electrode S located on the side of the control panel 2 facing away from the operator, and a counter electrode S' also located on the same side of the control panel 2. Both electrodes S and S' are designed to generate a measuring capacitance associated with the capacitive control panel. The electrode S and counter electrode S' are electrically insulated from each other and extend side by side, for example in a meandering or forked pattern, with the electrode S and the counter electrode S' being interwoven in such a way that gaps in one are filled by the other.

[0052] The capacitive sensor 3 includes an evaluation unit µC, in this case a microcontroller. This unit can be selectively electrically connected to electrode S to determine the potential applied to electrode S. Furthermore, the evaluation unit µC is also connected to the counter electrode S', is powered from the supply potential Vcc, and has a connection to ground. The evaluation unit µC is also configured to set the initial potential GND of electrode S, charge it, and selectively set the first ground potential GND' or, if applicable, the second ground potential GND'', as well as the influencing potential Vcc of the counter electrode S'.

[0053] Sensor 3 is trained to perform the following steps, which relate to Fig. 2 will be described below. Fig. Figure 2 shows the time potential profile U(t) of electrode S and the time potential profile, also referred to as counter potential U'(t), of counter electrode S' over a measurement cycle formed by steps i to viii described below, showing the case in which there is no contact or approach by the operator during the measurement cycle.

[0054] In a first step i, which is a first step of a sequence that is further formed from several steps ii to viii described below and which together form a measurement cycle, the electrode S is set to a predetermined initial electrical potential GND, which is preferably lower in magnitude than the first potential U1 and second potential U2 described below and usually preferably corresponds to the ground potential.

[0055] In a second step ii, following the first step i, beginning at time t0 and ending at time t1, the electrode S is charged, i.e., an electric charge is applied to the electrode S, and simultaneously the counter electrode S' is held at a first ground potential GND', which is lower in magnitude than the potential applied to the electrode S at least at the end time t1 of the second step. Both the charging and holding processes are carried out for a predetermined first time period. Preferably, the first ground potential GND' corresponds to the initial potential GND of the electrode S, and more preferably to the ground potential."Holding" in the sense of the invention preferably, but not necessarily, means a strict constant holding; rather, "holding" in the sense of the invention can imply a lower temporal variation of the relevant potential compared to "loading"; preferably, "holding" includes a temporal mean fluctuation over the relevant step of less than 10%.

[0056] In a third step iii following the second step ii at time t1, the counter electrode S' is subjected to an influencing potential VCC that differs from the first basic potential GND', for example the operating voltage of the previously described microcontroller as evaluation unit µC for a second time period Δt2 such that the influencing potential Vcc is greater in magnitude than the first basic potential GND' of the first step and the potential U(t2) applied to the electrode S at least finally at time t2 in this third step.

[0057] During or at the latest before the end of the second time period Δt2, in a fourth step iv, the evaluation unit µC, which was previously isolated from the electrode S, is connected to the electrode S.

[0058] At the latest at the end of the second time period Δt2, i.e. at time t2, in the fourth step iv a determination of an electrical first potential U1, which is set at the electrode S by means of the evaluation unit µC connected to the electrode S, by means of the influencing potential Vcc applied to the counter electrode S'.

[0059] In a subsequent fifth step v, beginning at time t2 and ending at time t3, the electrode S is again adjusted to the predetermined initial electrical potential GND, which is preferably lower in magnitude than the first potential U1 and the second potential U2 described below and corresponds, for example, to the ground potential, while the application of the influencing potential Vcc to the counter electrode S' is maintained.

[0060] In a subsequent sixth step vi, beginning at time t3 and ending at time t4, the electrode S is charged, i.e., an electric charge is applied to the electrode S and the counter electrode S' is simultaneously held at the influencing potential Vcc, i.e., charging and holding, for a predetermined third time period Δt3.

[0061] In the subsequent seventh step vii, beginning at time t4 and ending at time t5, the counter electrode S' is subjected to the first fundamental potential GND' or a second fundamental potential GND'', which differs from the first fundamental potential GND', for a predetermined fourth time period Δt4. This second potential is less than the potential U(t5) applied to the electrode S at least during the seventh step vii. During or at the latest before the end of the fourth time period Δt4, in an eighth step viii, the evaluation unit µC is connected to the electrode S, which was previously isolated from the evaluation unit µC. At the latest at the end of the fourth time period Δt4, i.e., at time t5, the evaluation unit µC, connected to the electrode S, determines a second electrical potential U2, which arises at the electrode S due to the first fundamental potential GND' or second fundamental potential GND'' applied to the counter electrode S'.

[0062] The aforementioned steps from step i to step viii are repeated multiple times in numerical order, each sequence constituting a measurement cycle. After each measurement cycle, the capacitive sensor 3 qualitatively and / or quantitatively determines a change in a quantity ΔU, derived from the first potential U1 determined in step iv and the second potential U2 determined in step viii, compared to a quantity determined in a previous measurement cycle, preferably the immediately preceding one (referred to here as the "baseline value"). This change is then used to detect contact or approach to the control panel 2, either positively or negatively, based on the change in quantity ΔU relative to the baseline value, and to output a corresponding detection result.In the present embodiment, the quantity ΔU is in each case a difference between the first potential U1 and the second potential U2, whereby only when a predetermined minimum absolute difference is undershot as a predetermined change in comparison is a touch or an approach to the control panel 2 positively detected.

[0063] The design of the control element 1 according to the invention has the advantage that temperature influences on the measuring capacitance, which result, for example, from mechanical changes of the electrodes S, S' involved, such as expansion or change in position, and thus from measuring capacitance, can be reduced or eliminated by the double determination of the electrode potential, namely the first potential U1 and second potential U2, in one measuring cycle, but with the opposite polarity of the counter-potential U'(t) applied to the counter-electrode S', namely once the influencing potential Vcc and the other time the first basic potential GND' or second basic potential GND''.It has been shown that while the temperature influence at most results in a change in the same direction of the potentials determined at electrode S, namely the first potential U1 and the second potential U2, the change in the two potentials determined in the fourth and eighth steps, namely the first potential U1 and the second potential U2, caused by approaching and touching the control panel 2, is in the opposite direction. This leads to the change in the quantity ΔU derived from the two previously determined potentials of first potential U1 and second potential U2 improving the touch or proximity detection by largely eliminating the influence of temperature on the measuring capacitance.

[0064] This shows Fig. 3 the dependence of the first potential U1 and second potential U2 determined at electrode S, whereby a linear proportionality is assumed for simplification, and T2>T1 holds.

[0065] Fig. In contrast, Figure 4 shows the behavior of the two potentials determined at electrode S, namely the first potential U1 determined in step iv, the second potential U2 determined in step viii, and the quantity ΔU derived from them, obtained here by taking the difference between the two aforementioned, on the one hand when B is touched in the time interval t6 <t<t8 im Vergleich zur Nichtberührung in den Zeitintervallen t<t6 und t> t8, which is in Fig. 4 is each marked by a crossed-out B. From time t7, the temperature decreases according to the Fig.3 starting from T1, ultimately reaching well after time t5T2. It turns out that if there is no contact in the time intervals t<t6 und t> The first potential U1(T1) increases to ultimately U1(T2), and the second potential U2 undergoes a similar variation, also increasing from U2(T1) to ultimately U2(T2), so that non-contact remains identifiable based on the quantity ΔU, essentially independent of temperature development. For the case of contact in the time interval t6

Claims

[1] Control element (1) with control panel (2) and capacitive sensor (3) for detecting an approach and / or touch of the control panel (2) by an operator, wherein the capacitive sensor (3) has on a side of the control panel (2) facing away from the operator an electrode (S) and a counter electrode (S') for generating a measuring capacitance associated with the capacitive control panel and an evaluation unit (µC) that can be selectively electrically connected to the electrode (S), wherein the capacitive sensor (3) is configured to perform a method comprising at least the following steps: i. Setting the electrode (S) to a predetermined initial electrical potential (GND); ii. subsequent charging of the electrode (S) and simultaneous holding of the counter electrode (S') at a first ground potential (GND') which is in magnitude less than the potential applied at the electrode (S) at least at the end, each for a predetermined first time period (Δt1); iii. subsequent application of an influencing potential (Vcc) to the counter electrode (S') that differs from the first basic potential (GND') such that the influencing potential (Vcc) is greater in magnitude than the first basic potential (GND') and the potential applied at least finally to the electrode (S) for a predetermined second time period (Δt2); iv. at the latest before the end of the second time period (Δt2) connect the evaluation unit (µC) to the electrode (S) and determine an electrical first potential (U1) that arises at the electrode (S) due to the influencing potential (Vcc) applied to the counter electrode (S') after the second time period (Δt2) by the evaluation unit (µC) connected to the electrode (S); v. subsequent adjustment of the electrode (S) to the predetermined initial electrical potential (GND) while maintaining the application of the influencing potential (Vcc) to the counter electrode (S'); vi. subsequent charging of the electrode (S) and simultaneous holding of the counter electrode (S') at the influencing potential (Vcc) each for a predetermined third time period (Δt3), vii. subsequent application of the first basic potential (GND') or a second basic potential (GND") that differs from the first basic potential (GND') and is lower in magnitude than the potential applied at least at the end of the electrode (S) for a predetermined fourth time period (Δt4); viii. at the latest before the expiry of the fourth time period (Δt4) connect the evaluation unit (µC) to the electrode (S) and determine a second electrical potential (U2) that arises at the electrode (S) due to the first basic potential (GND') or second basic potential applied to the counter electrode (S') after the expiry of the fourth time period (Δt4) by the evaluation unit (µC); Repeating steps i to viii multiple times in sequence, each forming a measurement cycle, and after each measurement cycle qualitatively and / or quantitatively determining a change in a quantity (ΔU) formed from the first potential (U1) and from the second potential (U2) compared to a previous quantity determined in a preceding, preferably the immediately preceding, measurement cycle by means of the capacitive sensor (3), in order to detect the touching or approaching the control panel (2) positively or negatively by means of the capacitive sensor (3) based on a change in the quantity (ΔU) compared to the previous quantity and to output a corresponding detection result by means of the capacitive sensor (3). [2] Control element (1) according to the preceding claim, wherein the capacitive sensor (3) is configured to compare the determined change in size (ΔU) compared to the original size with a predetermined reference change in order to detect, on the basis of the comparison, the touching of the control panel (2) or the approach to the control panel (2) positively or negatively. [3] Control element (1) according to the preceding claim, wherein a minimum change in the quantity (ΔU) below a predetermined amount is used from measurement cycle to measurement cycle for the subsequent adjustment of the predetermined comparison change. [4] Control element (1) according to one of the preceding claims, wherein the quantity (ΔU) is in each case a difference between the first potential (U1) and the second potential (U2) and only when a predetermined minimum absolute difference is undercut as a predetermined change in comparison is a touch or an approach to the control panel (2) positively detected. [5] Control element (1) according to one of the preceding claims, wherein the evaluation unit (µC) comprises an analog-to-digital converter (ADC) which is selectively connected to the electrode (S). [6] Control element (1) according to one of the preceding claims, wherein the initial potential (GND) and the first fundamental potential (GND') correspond to a ground potential. [7] Control element (1) according to one of the preceding claims, wherein the first time period (Δt1) and the third time period (Δt3) are each selected identically and / or the second time period (Δt2) and the fourth time period (Δt4) are each selected identically. [8] Use of the control element (1) according to any of the preceding claims in a motor vehicle. [9] Method for detecting an approach and / or touch of a control panel (2) of an operating element (1) by an operator, comprising an initial provisioning step in which the operating element (1) is provided with the control panel (2) and capacitive sensor (3), and wherein the capacitive sensor (3) has on a side of the control panel (2) facing away from the operator an electrode (S) and a counter electrode (S') for generating a measuring capacitance associated with the capacitive control panel and an evaluation unit (µC) selectively electrically connectable to the electrode (S); further comprising the following steps: i. Setting the electrode (S) to a predetermined initial electrical potential (GND); ii. subsequent charging of the electrode (S) and simultaneous holding of the counter electrode (S') at a first ground potential (GND') which is in magnitude less than the potential applied at the electrode (S) at least at the end, each for a predetermined first time period (Δt1); iii. subsequent application of an influencing potential (Vcc) to the counter electrode (S') that differs from the first basic potential (GN D') such that the influencing potential (Vcc) is greater in magnitude than the first basic potential (GND') and the potential at least finally applied to the electrode (S) for a predetermined second time period (Δt2); iv. at the latest before the end of the second time period (Δt2) connect the evaluation unit (µC) to the electrode (S) and determine an electrical first potential (U1) that arises at the electrode (S) due to the influencing potential (Vcc) applied to the counter electrode (S') after the second time period (Δt2) by the evaluation unit (µC) connected to the electrode (S); v. subsequent adjustment of the electrode (S) to the predetermined initial electrical potential (GND) while maintaining the application of the influencing potential (Vcc) to the counter electrode (S'); vi. subsequent charging of the electrode (S) and simultaneous holding of the counter electrode (S') at the influencing potential (Vcc) each for a predetermined third time period (Δt3), vii. subsequent application of the first basic potential (GND') or a second basic potential (GND'') that differs from the first basic potential (GND') and is lower in magnitude than the potential applied at least at the end of the electrode (S) for a predetermined fourth time period (Δt4); viii. at the latest before the expiry of the fourth time period (Δt4) connect the evaluation unit (µC) to the electrode (S) and determine a second electrical potential (U2) that arises at the electrode (S) due to the first basic potential (GND') or second basic potential applied to the counter electrode (S') after the expiry of the fourth time period (Δt4) by the evaluation unit (µC);Repeatedly repeating steps i to viii in sequence, each of which constitutes a measurement cycle, and after each measurement cycle qualitatively and / or quantitatively determining a change in a quantity (ΔU) formed from the first potential (U1) and from the second potential (U2) compared to a previously determined value in a preceding, preferably the immediately preceding, measurement cycle by means of the capacitive sensor (3), in order to detect, based on the change, the touching or approach to the capacitive control panel (2) positively or negatively by means of the capacitive sensor (3) and to output a corresponding detection result by means of the capacitive sensor (3). [10] Method according to the preceding claim, wherein the capacitive sensor (3) is configured to compare the determined change in size (ΔU) compared to the original size with a predetermined reference change in order to detect, on the basis of the comparison, the touching of the control panel (2) or the approach to the control panel (2) positively or negatively. [11] Method according to the preceding claim, wherein a minimum change in the quantity (ΔU) below a predetermined amount is used from measurement cycle to measurement cycle for the subsequent adjustment of the predetermined comparison change. [12] Method according to any of the preceding claims 9 to 11, wherein the quantity (ΔU) is in each case a difference between first potential (U1) and second potential (U2) and only when a predetermined minimum absolute difference is undercut as a predetermined change in comparison is a touching of the control panel (2) or an approach to the control panel (2) positively detected. [13] Method according to any one of the preceding claims 9 to 12, wherein the evaluation unit (µC) comprises an analog-to-digital converter (ADC) for selective connection with the electrode (S). [14] Method according to any one of the preceding claims 9 to 13, wherein the initial potential (GND) and the first ground potential (GND') correspond to a ground potential. [15] Method according to any one of the preceding claims 9 to 14, wherein the first time period (Δt1) and the third time period (Δt3) are each selected identically and / or the second time period (Δt2) and the fourth time period (Δt4) are each selected identically.

Images