Device for fail-safe touch detection

Abstract

The invention relates to a device (1) for fail-safe detection of a touch of a surface, comprising a primary sensor (10) having at least one measurement path (11) formed by a functional conductor, which is assigned to a region (2) of the surface, a reference sensor (20) having at least one reference path (21) and an evaluation device (30) connected for signalling purposes to the primary sensor (10) and to the reference sensor (20), wherein each measurement path (11) is assigned at least one reference path (21), wherein the primary sensor (10) is designed to detect impedance and capacitance changes, which can be caused by a touch of the region (2) of the surface or by interference on the measurement path (11), as measurement values (X), and the reference sensor (20) is designed to detect impedance and / or capacitance changes, which can be caused exclusively by interference on the reference path (21), as reference values (Y), and wherein the evaluation device (30) is designed to determine, from measurement values (X) and reference values (Y), values (Z) adjusted for the interference, from which it can be determined whether the surface is touched.

Description

[0001] Device for fail-safe touch detection

[0002] Description:

[0003] The invention relates to a device for the fail-safe detection of a contact with a surface, in particular a surface of a steering handle of a vehicle.

[0004] A variety of surfaces and steering handles are known from the state of the art on which a touch is to be detected.

[0005] These touch detection systems are often based on a touch-induced capacitance or impedance change on a current-carrying electrical conductor. However, this is problematic because the sensor that detects the capacitance or impedance changes, or a measurement path of the sensor, can also be subject to interference, which can distort the measurement and thus the determination of touch detection.

[0006] Such interference or disturbances can be, for example, electromagnetic fields, fluctuations in the vehicle electrical system or fluctuations in the supply voltage or other fluctuating environmental influences, such as humidity or temperature.

[0007] Accordingly, it can happen that touches are detected even though no contact is made with the surface, or conversely, that no contact is detected even though the surface is touched by a user.

[0008] This is particularly disadvantageous when touch detection is used for safety functions, as is common in modern vehicles. For example, hand detection on the steering handle is often required at the time of registration for the use of autonomous or automated driving.

[0009] It is therefore desirable to improve touch detection and make it more robust and less prone to errors.

[0010] Various approaches to this are already known from the state of the art, but some of them still need to be improved.

[0011] For example, DE 10 2014 117 821 A1, DE 11 2017 000 507 T5, EP 3 227 161 B1, and EP 3 227 163 B1 teach the use of a measuring circuit and a reference circuit, which together serve to detect a touch on a steering handle of a motor vehicle. However, these devices are generally based on the fact that the reference circuit must be evaluated before or after the actual touch detection, which is time-consuming and still allows errors to occur during the actual touch detection, particularly errors due to interference with fluctuating disturbance variables.

[0012] The invention is therefore based on the object of overcoming the aforementioned disadvantages and of providing a device and in particular a steering handle on and with which a touch by a user can be detected essentially free from interference.

[0013] This problem is solved by the combination of features according to patent claim 1.

[0014] According to the invention, a device is therefore proposed for the fail-safe detection of contact with a surface, wherein the surface is in particular the surface of a steering handle of a vehicle. The device has a primary sensor with at least one measuring path formed by a functional conductor, which is assigned to a region of the surface, a reference sensor with at least one reference path, and an evaluation device connected to the primary sensor and the reference sensor in terms of signal technology. It is essential to the invention that each measuring path is assigned at least one reference path, which is preferably designed as a copy of the measuring path. The term "copy" is understood to mean that the reference path has physical properties that are as identical as possible and in particular identical to those of the respectively assigned measuring path, so that disturbances act essentially identically on the measuring path and the reference path.For example, the length, dimensions and course of the reference path and the measuring path are accordingly as identical as possible and preferably identical, with the reference path being arranged at a distance from the measuring path. In order to be able to detect contact with the surface, the primary sensor is designed to detect impedance and / or capacitance changes that are caused or can be caused by contact with the area of ​​the surface or by interference on the measuring path, as measured values. In contrast, the reference sensor is designed to detect impedance and / or capacitance changes that are caused or can be caused exclusively by interference on the reference path, as reference values. Contact with the surface accordingly has no influence on the reference sensor or its reference path and in particular does not cause any impedance and / or capacitance changes on the reference path.This can be ensured, for example, by appropriate shielding and / or arrangement of the reference path, which in a simple case is arranged such that contact with the surface or at least contact with the area of ​​the surface assigned to the measurement path does not lead to a change in impedance and / or capacitance in or at the reference path. Furthermore, the evaluation device is designed to determine values ​​from measured values ​​and reference values ​​that have been adjusted for interference, from which it can be determined whether the surface or the area of ​​the surface assigned to the measurement path is touched.

[0015] The fundamental inventive idea is to sensorically evaluate two essentially identical paths (measurement path and reference path), whereby disturbances or interferences affect both paths essentially identically, but a user touch only affects one path (measurement path). Accordingly, the signal of the measurement path can be adjusted for the interference and its magnitude (disturbance), for example, by subtracting the signal from the reference path, resulting in a signal or value adjusted for the interference. The adjusted value can then be evaluated, for example, by comparing it with a threshold value for touch detection.

[0016] Although multiple reference paths can be assigned to each measurement path to improve evaluation, preferably exactly one reference path is assigned to each measurement path. In this case, at least one common, and in particular a single common, reference path can be assigned to multiple identically configured measurement paths, so that one reference path can be assigned to a measurement path, but multiple measurement paths can be assigned to a reference path. If multiple reference paths are assigned to a measurement path, their reference values ​​can be processed beforehand, for example by calculating an average, before the adjusted values ​​are determined from the processed values ​​and the measured values.

[0017] Preferably, the at least one measuring path consists of exactly one functional conductor. As explained below, a respective reference path can additionally have a capacitance or capacitor, but otherwise preferably consists of only one reference conductor, which in particular is not a functional conductor, since the reference conductor, although preferably having identical properties to the functional conductor, does not serve as a heating wire.

[0018] Furthermore, the functional conductor can be designed to simultaneously serve as a heating wire for heating the surface. For this purpose, the functional conductor of the measuring path can be alternately connected to a sensor control for detecting contact with the surface and a heating control for heating the surface.

[0019] In order to be able to take into account fixed influences on the measuring path and in particular the capacitance measurable on the measuring path, such as those resulting from the specific installation situation of the measuring path, also on the reference sensor or the reference path, an advantageous variant provides that the reference sensor has a reference capacitance for each reference path, which corresponds to the capacitance that can be measured with the measuring path belonging to the respective reference path when the area of ​​the surface to which the measuring path is assigned is contact-free.

[0020] The reference capacitance can, for example, be connected to the reference path and to a mass which corresponds in particular to a mass of the reference path.

[0021] In addition, the primary sensor can have two switches per measurement path, between which the measurement path extends and by which the measurement path can be completely decoupled from a voltage source and / or ground. Furthermore, the measurement path can also be electrically connected to the heating control system via the switches. Additionally or alternatively, the reference sensor can also have two switches per reference path, between which the reference path extends and by which the respective reference path can be completely decoupled from a voltage source and ground.

[0022] Preferably, the reference path or the reference sensor is decoupled from the voltage source and / or the earthing with which in particular the measuring path or the primary sensor is contacted.

[0023] A second or separate voltage source (stabilized power supply, battery or accumulator) can be provided for the reference sensor or the reference path, whereby this can be charged or supplied via the voltage source of the primary sensor.

[0024] An advantageous further development of the device also provides that the evaluation device is designed to carry out a subtraction, a vectorial subtraction, and / or an absolute value comparison of measured values ​​and reference values ​​or of values ​​based thereon, such as an impedance determined therefrom, in order to thereby determine the adjusted value.

[0025] A further aspect of the invention relates to a steering handle with a device according to the invention. The steering handle has a surface which is divided into several areas. Furthermore, a measuring path is assigned to each area. The surface of the steering handle is understood in particular to be the part of the surface which is gripped by a user during intended use. For example, the surface can have a first (visible side) area which faces the user and a second (rear side) area which faces away from the user. Depending on whether a touch is detected in the first area or the second area, a distinction can be made as to whether the user's hand is resting on the visible side or the back of the steering handle.

[0026] The reference paths corresponding to the measuring paths can be arranged in the steering handle itself, whereby they are arranged in such a way that they are not grasped or cannot be grasped by the user during the intended use of the steering handle.

[0027] For example, if the steering handle has an area for activating the horn, the reference paths can be located in this area, as this area is typically only touched by the user on rare occasions. If the user activates the horn, this can be detected by a corresponding sensor, which is independent of the primary or reference sensor, and taken into account by the evaluation device. Alternatively, the reference paths can also be shielded by material so that contact adjacent to the reference paths has no effect on them.

[0028] A further aspect of the invention also relates to a method for fail-safe touch detection of a surface using a device according to the invention or a steering handle according to the invention. The method comprises the following steps: a. Recording the measured values ​​with the primary sensor, ie in particular recording the measured values ​​on the at least one measuring path and preferably simultaneously recording the reference values ​​with the reference sensor, ie in particular recording the reference values ​​on the at least one reference path; b. Calculating the complex impedance of the at least one measuring path from the measured values ​​and the complex impedance of the at least one reference path from the reference values; c. Determining adjusted values ​​from the complex impedance of the at least one measuring path and the complex impedance of the at least one reference path; d. Comparing the adjusted values ​​with a threshold value above which contact with the surface is assumed.

[0029] Furthermore, it can be provided that the adjusted values ​​in step c are determined by subtraction or by vectorial subtraction of the complex impedance of the reference path from the complex impedance of the measuring path or by comparing their absolute values.

[0030] In addition, noise in the reference values ​​can be determined, particularly before step b. The noise is compared with a noise threshold. If the noise exceeds the noise threshold, an error is detected or assumed, i.e., the noise or its noise value is checked for plausibility. This error or the verification of the noise can be considered, saved, and / or displayed in the subsequent evaluation.

[0031] The noise can be determined by determining the standard deviation and / or the variance of the reference values.

[0032] The evaluation device is preferably designed to carry out the steps of the method and / or the determination and plausibility check of the noise.

[0033] The features disclosed above can be combined as desired, as long as this is technically possible and they do not contradict each other.

[0034] Other advantageous developments of the invention are characterized in the subclaims or are presented in more detail below, together with the description of the preferred embodiment of the invention, with reference to the figures. They show:

[0035] Fig. 1 shows a device for fail-safe detection of contact with a surface;

[0036] Fig. 2 a process for determining a touch.

[0037] The figures are schematic examples. Identical reference numerals in the figures indicate identical functional and / or structural features.

[0038] Figure 1 shows a schematic device 1 for detecting a touch on a surface, preferably the surface of a steering handle of a vehicle. For example, the surface has or corresponds to an area 2, wherein the area 2 or the surface of the steering handle is to be monitored for touch by the user U.

[0039] The measuring path 11 of the primary sensor 10 is assigned to this area 2, so that touching the area 2 causes a change in the capacitance and the impedance on the measuring path 11, which can be detected by the primary sensor 10.

[0040] The surface can also have several areas 2, in which case each area 2 would be assigned a primary sensor 10 with at least one measuring path 11.

[0041] If the user U does not touch the surface or area 2 of the surface, a resting capacitance of Csen is established at the measuring path 11.

[0042] In addition, the device 1 has a reference sensor 20 with a reference path 21. In order to take into account the installation situation of the measuring path 11, the reference sensor 20 further has a reference capacitance 22 with a capacitance Cp e f, which corresponds to the rest capacitance Csen of the measuring path 11.

[0043] If several primary sensors 10 and reference sensors 20 are present, these can be connected to a common evaluation device 30 for signal processing purposes.

[0044] Accordingly, a touch by the user U leads to a change in capacitance or impedance only at the measurement path 11, but not at the reference path 21. Interference, however, essentially affects both the measurement path 11 and the reference path 21.

[0045] Isolated interference influences or disturbance variables can also affect the reference path 21. To compensate for or detect and take into account at least some of such interference influences acting on the reference path 21, a plurality of reference paths 21 can be provided, which can be arranged at a distance from one another, although this is not shown here for the sake of clarity. The primary sensor 10 has a sensor controller 15 for determining the measured values ​​X, and the reference sensor 20 has a sensor controller 25 for determining the reference values ​​Y. In the present case, these are integrated together with the evaluation device 30 in a common electronics unit 40, but can also be designed separately and connected to one another merely for signaling purposes.

[0046] The sensor controller 15 of the primary sensor 10 and the sensor controller 25 of the reference sensor 20 determine the capacitance and / or impedance at the measuring path 11 and the reference path 21, respectively, within the scope of touch detection. The measured value X and the reference value Y, or values ​​determined therefrom, are forwarded to the evaluation device 30, which then determines adjusted values ​​Z from these, from which it can be reliably determined whether the area 2 is touched by the user U.

[0047] The measuring path 11 and the reference path 21 each extend between two switches 13, 14, 23, 24, by which the respective path can be completely enabled.

[0048] The measuring path 11 can be connected to ground or GND and, via a contact 16, preferably to a (first) voltage source (not shown). The reference path 21 can be further connected to the ground or GND of the measuring path 11 or, preferably, completely decoupled from the ground or GND of the measuring path 11 and the (first) voltage source of the measuring path 11 and, for example, connected via a contact 26 to a separate (second) voltage source (also not shown here) and a correspondingly separate ground.

[0049] Furthermore, the entire reference sensor 20 can, in particular, have a capacitance Cpar, which can be correspondingly detected as a reference value. Figure 2 shows an exemplary method, based on a flowchart, for determining the adjusted values ​​Z and a touch detection based thereon.

[0050] The procedure includes the following steps:

[0051] A Determination of the reference values ​​Y with the reference sensor 20;

[0052] B Determining a noise of the reference values ​​Y;

[0053] C Does the noise exceed a predetermined noise threshold?

[0054] D if yes, there is an error; save, display or correct the error

[0055] E if no, there is no error;

[0056] F Determination of the measured values ​​X with the primary sensor 10, preferably simultaneously with step A;

[0057] G Calculation of the complex impedance of the measuring path 11 from the measured values ​​X and the complex impedance of the reference path 21 from the reference values ​​Y;

[0058] H Subtraction of the complex impedance of the reference path 21 from the complex impedance of the measuring path 11;

[0059] I The subtraction results in the adjusted value Z, from which, if it exceeds or falls below a predetermined threshold value, it can be concluded that the area 2 has been touched by the user U.

[0060] In particular, steps A and F are carried out by the respective sensor 10, 20 and steps B to E and G to I are carried out by or through the evaluation device 30, which is designed accordingly for this purpose.

Claims

Patent claims 1. Device (1) for the fail-safe detection of a touch of a surface by a user (II), comprising a primary sensor (10) with at least one measuring path (11) formed by a functional conductor, which is assigned to a region (2) of the surface, a reference sensor (20) with at least one reference path (21), and an evaluation device (30) connected to the primary sensor (10) and the reference sensor (20) for signal transmission, wherein at least one reference path (21) is assigned to each measuring path (11), wherein the primary sensor (10) is designed to detect impedance and / or capacitance changes, which can be caused by touching the region (2) of the surface or by interference on the measuring path (11), as measured values ​​(X), and the reference sensor (20) is designed to detect impedance and / or capacitance changes, which can be caused exclusively by interference on the reference path (21), as reference values ​​(Y).and wherein the evaluation device (30) is designed to determine values ​​(Z) adjusted for the interference from measured values ​​(X) and reference values ​​(Y), from which it can be determined whether the surface is touched., 2. Device according to claim 1, wherein the functional conductor of the measuring path (11) can be connected to a heating control and is designed to serve at the same time as a heating wire for heating the surface.

3. Device according to claim 1 or 2, wherein the reference sensor (20) has a reference capacitance (22) for each reference path (21), which corresponds to the capacitance that can be measured with the measuring path (11) belonging to the respective reference path (21) when the area (2) of the surface to which the measuring path (11) is assigned is contact-free.

4. Device according to one of the preceding claims, wherein the primary sensor (10) has two switches (13, 14) for each measuring path (11), between which the measuring path (11) extends and by means of which the respective measuring path (11) can be completely decoupled from a voltage source and an earthing connection and / or the reference sensor (20) has two switches (23, 24) for each reference path (21), between which the reference path (21) extends and by means of which the respective reference path (21) can be completely decoupled from a voltage source and an earthing connection.

5. Device according to one of the preceding claims, wherein the evaluation device (30) is designed to carry out a subtraction, a vectorial subtraction, and / or an absolute value comparison of measured values ​​(X) and reference values ​​(Y) or values ​​based on the measured values ​​(X) and the reference values ​​(Y) in order to thereby determine the adjusted value (Z).

6. Steering handle with a device (1) according to one of the preceding claims, wherein the steering handle has a surface which is divided into several areas (2), wherein each of the areas (2) is assigned a measuring path (11).

7. Method for fail-safe touch detection of a surface with a device (1) according to one of the preceding claims, comprising the following steps: a. detecting the measured values ​​(X) with the primary sensor (10) and the reference values ​​(Y) with the reference sensor (20); b. calculating the complex impedance of the at least one measuring path (11) from the measured values ​​(X) and the complex impedance of the at least one reference path (21) from the reference values ​​(Y); c. determining adjusted values ​​(Z) from the complex impedance (X) of the at least one measuring path (11) and the complex impedance (Y) of the at least one reference path (21); d. comparing the adjusted values ​​(Z) with a threshold value above which contact with the surface is assumed.

8. Method according to the preceding claim, wherein the adjusted values ​​(Z) in step c are determined by subtraction or by vectorial subtraction of the complex impedance of the reference path (21) from the complex impedance of the measuring path (11) or by comparing their absolute values.

9. Method according to one of the two preceding claims, wherein a noise of the reference values ​​(Y) is determined, the noise is compared with a noise threshold value and an error is detected if the noise exceeds the noise threshold value.

10. Method according to the preceding step, wherein the noise is determined by determining the standard deviation and / or the variance of the reference values ​​(Y).

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