WO2023088825A1

WO2023088825A1 - Fault detection during operation of a device for detecting contact with a capacitive element

Info

Publication number: WO2023088825A1
Application number: PCT/EP2022/081728
Authority: WO
Inventors: Martin Schmitt; Ciprian Musat
Original assignee: Valeo Schalter Und Sensoren Gmbh
Priority date: 2021-11-17
Filing date: 2022-11-14
Publication date: 2023-05-25
Also published as: DE102021129932A1

Abstract

According to a method for fault detection during operation of a device for detecting contact with a capacitive element (3), the capacitive element (3) is charged during each measurement cycle of a plurality of successive measurement cycles and subsequently an amount of charge of the capacitive element (3) is transferred to a further capacitive element (5) within the same measurement cycle. After the plurality of measurement cycles, a measurement value relating to a total amount of charge transferred overall to the further capacitive element (5) during the plurality of measurement cycles is determined. It is checked whether the measurement value is smaller than or equal to a predetermined first threshold value and whether the measurement value is larger than or equal to a predetermined second threshold value. Depending on a result of the check, the presence of a fault is established and a fault type of the fault is determined.

Description

Error detection in the operation of a device for detecting a touch of a capacitive element

The present invention relates to a method for error detection when operating a device for detecting a touch of a capacitive element, wherein the capacitive element is charged during each measurement cycle of a plurality of consecutive measurement cycles and then a charge amount is transferred from the capacitive element to another capacitive element and after the plurality of measurement cycles, a measured value relating to a total amount of charge transferred to the further capacitive element during the plurality of measurement cycles. The invention also relates to a method for detecting user input that includes a user touching a capacitive element, a device for detecting touching a capacitive element, a user input device with such a device, a motor vehicle with such a user input device, and a computer program product.

Document US Pat. No. 6,466,036 B1 specifies a pulse circuit for measuring the capacitance of a sensor plate, which is capable of repeatedly transferring charge accumulated on the sensor plate to a capacitor and, after a large number of repetitions, reading out the amount of charge transferred or reading out a corresponding voltage. to determine the capacitance of the sensor pad. Such a method is also referred to as a Q-Charge method.

Such circuits can be used, for example, for the capacitive detection of user inputs, with the approach or touch of the sensor plate by the user changing the capacitance of the sensor plate and the touch or approach being able to be detected as a result. In particular, such a touch detection can be used for applications in the interior of motor vehicles, for example when detecting the actuation of touch-sensitive control panels or control elements.

It is an object of the present invention, when detecting a touching of a capacitive element in the manner described at the outset, to specify a possibility for fault detection and in particular for fault classification. This object is solved by the respective subject matter of the independent claims. Advantageous developments and preferred embodiments are the subject matter of the dependent claims.

The invention is based on the idea of checking the total amount of charge transferred to the further capacitive element after the large number of measurement cycles using the measured value in such a way that it is determined whether the measured value is less than or equal to a first threshold value or whether it is greater than or equal to a second threshold value is. Depending on this, the error type of the error is determined.

According to one aspect of the invention, a method for error detection when operating a device for detecting a touch of a capacitive element is specified. In this case, the capacitive element is charged, for example fully charged, during each measurement cycle of a plurality of successive measurement cycles, and then within the same measurement cycle a quantity of charge is transferred from the capacitive element to a further capacitive element. In other words, the capacitive element is charged in each measuring cycle and part of the charge is transferred from the capacitive element to the further capacitive element. After the large number of measuring cycles, i.e. in particular after the end of all measuring cycles of the large number of measuring cycles, a measured value relating to a value transmitted during the large number of measuring cycles overall to the further capacitive element, in particular from the capacitive element to the further capacitive element, is transmitted, in particular by means of an evaluation unit element transferred, total amount of charge determined. It is checked, in particular by means of the evaluation unit, whether the measured value is less than or equal to a predetermined first threshold value and it is checked, in particular by means of the evaluation unit, whether the measured value is greater than or equal to a predetermined second threshold value. The second threshold is greater than the first threshold. Depending on a result of the check, the presence of an error is determined and an error type of the error is determined, in particular by means of the evaluation unit.

To determine the measured value, for example, a voltage present at the further capacitive element or the voltage drop across the further capacitive element can be measured. The measured value therefore corresponds in particular to a voltage value or depends on a corresponding voltage value of the further capacitive element. In particular, the voltage measurement for determining the measured value only takes place when the large number of measurement cycles has ended. In preferred embodiments, the measured value corresponds to a difference between the voltage value and a reference voltage value.

The reference voltage value can be, for example, a previous voltage value of the further capacitive element measured before the plurality of consecutive measurement cycles.

Instead of comparing the voltage value measured after the plurality of measurement cycles directly with the threshold value or comparing its difference to a fixed reference value with the threshold value, a dynamically tracked reference voltage value can be implemented in this way. In particular, the change in the voltage which is present at the further capacitive element is then detected. In particular, this change may be due to a user touching the capacitive element and a resulting increase in the capacitance of the capacitive element. Consequently, in a single measurement cycle, the charge increases from the capacitive element to the further capacitive element and thus also the total amount of charge. The dynamically tracked reference voltage value can be used to compensate for temperature fluctuations, for example, so that more reliable touch detection is made possible. However, if such fluctuations are negligible, a static reference voltage value can also be used.

The amount of charge transferred from the capacitive element to the further capacitive element during a measurement cycle does not necessarily correspond exactly to the amount of charge that was loaded onto the capacitive element during the charging of the capacitive element during the same measurement cycle. For example, when charging the capacitive element, a charge equalization between the capacitive element and the further capacitive element can be suppressed and the charge equalization between the capacitive element and the further capacitive element can be allowed to transfer the amount of charge.

While the charge accumulates on the further capacitive element over the course of the large number of successive measurement cycles to form the total amount of charge, the capacitive element can be discharged, ie reset, for example after each individual measurement cycle or within each individual measurement cycle. A measuring cycle can therefore contain a number of successive sections which correspond to different states of the capacitive element and the further capacitive element or of a circuit with the capacitive element and the further capacitive element. The capacitive element can be designed as a capacitor, for example, or contain a single sensor area, in which case the capacitance of the capacitive element can then be given, for example, by the intrinsic capacitance of the sensor area, for example with respect to a ground potential.

The additional capacitive element can also be designed as a capacitor. The dimensioning of the further capacitive element is selected in particular in such a way that a capacitance of the further capacitive element is many times greater than a maximum capacitance of the capacitive element. For example, the ratio of the capacitance of the further capacitive element to the maximum capacitance of the capacitive element can be in the range from 10 to 1000, in particular in the range from 100 to 1000.

The evaluation unit can also be regarded as an arithmetic unit or contain an arithmetic unit. A computing unit can be understood in particular as a data processing device, so the computing unit can in particular process data for carrying out computing operations. This may also include operations to perform indexed accesses to a data structure, for example a look-up table (LUT).

In particular, the processing unit can contain one or more computers, one or more microcontrollers and/or one or more integrated circuits, for example one or more application-specific integrated circuits, ASICs (English: “application-specific integrated circuit”), one or more field-programmable gate Arrays, FPGA, and/or one or more single-chip systems, SoC (English: "system on a chip"). The computing unit can also have one or more processors, for example one or more microprocessors, one or more central processing units, CPU, one or more graphics processor units, GPU and/or contain one or more signal processors, in particular one or more digital signal processors, DSP. The processing unit can also be a physical or contain a virtual network of computers or other units mentioned.

In various exemplary embodiments, the computing unit includes one or more hardware and/or software interfaces and/or one or more memory units.

Depending on the measured value, the evaluation unit can, for example, determine the capacitance of the capacitive element depending on the measured value, in particular if there is no error. Since the capacitance of the capacitive element is determined indirectly via the total amount of charge transferred to the other capacitive element, the accuracy of the capacitance determination can be significantly increased, since the much lower voltages that are present at the capacitive element itself are not measured and evaluated Need to become.

The device for detecting touching of the capacitive element, in particular by a user, can in particular contain the evaluation unit and the circuit with the capacitive element and the further capacitive element. The error can then in particular be an error in the device or in the device or in the supply or in the operation of the device.

In particular, the error is an error that influences the measured value. It can therefore be an open circuit, also referred to as an open load or open circuit, for example, in which a connecting line between the capacitive element and the further capacitive element is interrupted or partially interrupted. The error can also be a short circuit of the connecting line to another connection, for example a reference potential connection, in particular a ground connection, or a voltage supply connection.

Depending on whether and what type of error is present, i.e. what type of error is present, this has different effects on the measured value. If, for example, there is an open circuit, the capacitive element can be charged less, for example, than would be the case with error-free operation. Accordingly, less charge quantity can be transferred from the capacitive element to the further capacitive element. Accordingly, the measured value is smaller than would be expected in error-free operation. A similar situation occurs when a short circuit to the ground potential is present. Here the charge of the capacitive element or the transfer of charge to the further capacitive element can come to a complete standstill, so that the measured value is ultimately even lower. In the event of a short circuit to the supply voltage, the further capacitive element is fully charged, for example, so that the same maximum voltage is always read out after the end of the large number of measurement cycles. Accordingly, the measured value is significantly higher than can be expected in error-free operation.

By providing two or more threshold values according to the invention and analyzing the measured value to determine whether it is greater than or equal to the second threshold value and whether it is less than or equal to the first threshold value, different error types can be identified. Accordingly, different measures can be initiated, depending on the type of error.

In order to check whether the measured value is less than or equal to the first threshold and whether the measured value is greater than or equal to the second threshold, the evaluation unit can, for example, compare the measured value with the first threshold and, if the measured value is greater than the first threshold, the Also compare the measured value with the second threshold value.

Here and in the following it is assumed that the measured value is positive. Alternatively, the measured value can also be understood as the absolute value of a negative measured value. If necessary, the signs and inequalities are to be inverted accordingly.

In accordance with at least one embodiment of the method, the measured value is compared with the first threshold value. If the measured value according to the comparison with the first threshold value is less than or equal to the first threshold value, then the presence of the error is determined and the error is assigned to a predefined first error type.

The comparison of the measured value with the first threshold value can in particular be regarded as part of the check as to whether the measured value is less than or equal to the predetermined first threshold value. In particular, by assigning the error to the first error type, the error type is determined to be the first error type.

The first type of error can correspond, for example, to a short circuit in the electrical connecting line between the capacitive element and the further capacitive element to ground potential. The first type of error can also be a situation in which either a short circuit to ground potential or an open circuit exists, not determining which of the two situations exists. Depending on the size of the first threshold value, both variants can be implemented.

In accordance with at least one embodiment, the measured value is compared to the second threshold value if, in particular only if or precisely when, the measured value is greater than the first threshold value. If the measured value according to the comparison with the second threshold value is greater than or equal to the second threshold value, then the presence of the error is determined and the error is assigned to a second error type.

The comparison of the measured value with the second threshold value can be understood in particular as part of the check as to whether the measured value is greater than or equal to the second threshold value. In particular, by associating the error with the second error type, the error type is determined to be the second error type.

The second type of error can correspond in particular to a short circuit in the electrical connection line between the capacitive element and the further capacitive element to the supply voltage connection. The supply voltage connection can be used, for example, to connect a voltage source to the capacitive element in order to charge the capacitive element during the multiplicity of measurement cycles.

In accordance with at least one embodiment, the measured value is compared to a third predefined threshold value if, in particular only if or precisely when the measured value is greater than the first threshold value. If the measured value according to the comparison with the third threshold value is less than or equal to the third threshold value, then the presence of the error is determined and the error is assigned to a third error type.

The comparison of the measured value with the third threshold value takes place in particular before the measured value is optionally compared with the second threshold value in corresponding embodiments. In particular, the third threshold is greater than the first threshold and less than the second threshold. In such specific embodiments, the first error type can correspond, for example, to the short circuit to the reference potential connection, ie to the ground potential connection, and the third error type can correspond to the open circuit.

By initially comparing with the first threshold value and only then comparing with the third threshold value if the measured value is greater than the first threshold value, the corresponding error types can be unambiguously assigned.

According to at least one embodiment, the measured value is compared to the second threshold value if, in particular only if, for example exactly when the measured value is greater than the third threshold value.

In particular, the first type of error can correspond to the short circuit in the connecting line between the capacitive element and the further capacitive element with the reference potential connection and/or the third type of error can correspond to an interruption or partial interruption of the electrical connecting line, i.e. an open circuit, and/or the second type of error can correspond to the short circuit correspond to the connection line with the supply voltage connection.

According to at least one embodiment, it is determined, in particular by means of the evaluation unit, that the error is not present if the measured value according to the comparison with the second threshold value is less than the second threshold value.

In particular, it is established that the error is not present if, according to the comparisons described, the measured value is greater than the first threshold value, greater than the third threshold value and less than the second threshold value.

According to at least one embodiment, each of the measurement cycles includes a charging portion, wherein the charging of the capacitive element occurs during the charging portion. Each of the measurement cycles includes a transfer section, with the charge quantity being transferred from the capacitive element to the further capacitive element during the transfer section.

The transmission section follows the loading section of the same measurement cycle, but does not necessarily follow it immediately. In particular, each measurement cycle of the plurality of measurement cycles includes a plurality of consecutive sections including the loading section and the transmission section. According to at least one embodiment, each of the measurement cycles includes an intermediate portion between the charging portion and the transmitting portion, wherein the capacitive element is neither charged nor discharged during the intermediate portion. According to at least one embodiment, each of the measurement cycles has a further intermediate section before the charging section or after the transmission section, wherein the capacitive element is neither charged nor discharged during the further intermediate section.

For example, each measurement cycle may include or consist of the loading section, the intermediate section, the transmission section, and the further intermediate section in that order. Alternatively, each of the measurement cycles may include or consist of the further intermediate section, the charging section, the intermediate section, and the transmission section, in that order.

As explained above, a charge equalization between the capacitive element and the further capacitive element can be prevented during the charging section and allowed during the transmission section by appropriate wiring of the capacitive element and the further capacitive element. The intermediate sections prevent leakage currents from the further capacitive element from falsifying the measurement when switching over from the charging section to the transmission section or vice versa.

According to a further aspect of the invention, a method for detecting a user input is also provided, the user input including a user touching a capacitive element. The method for detecting a user input includes carrying out a method for error detection according to the invention. The user input or the touch is determined depending on the measured value, in particular by means of the evaluation unit, in particular if it is determined based on the result of the check that the error is not present.

For example, the evaluation unit can compare the measured value with a further threshold value that is greater than the first threshold value and smaller than the second threshold value. In particular, the further measured value is greater than the third threshold value. The user input or the touch is detected if the measured value according to the comparison with the further threshold value is greater than the further threshold value and in particular less than the second threshold value. According to a further aspect of the invention, a device for detecting a touch of a capacitive element is specified. The device has a terminal to connect the capacitive element to the device. The device has a circuit that is set up to connect the capacitive element to a voltage source during each measurement cycle of a plurality of successive measurement cycles in order to charge the capacitive element and subsequently, within the same measurement cycle, transfer an amount of charge from the capacitive element to another capacitive element To transfer element of the device. The device has an evaluation unit which is set up to determine, after the plurality of measurement cycles, a measured value relating to a total amount of charge transferred to the further capacitive element during the number of measurement cycles. The evaluation unit is set up to check whether the measured value is less than or equal to a predefined first threshold value and whether the measured value is greater than or equal to a predefined second threshold value. The evaluation unit is set up to determine the presence of an error and to determine an error type of the error depending on a result of the check.

In general, the capacitive element is not necessarily part of the device. In various embodiments, however, the device, in particular the circuit, can include the capacitive element. The further capacitive element can also be part of the circuit, for example.

Likewise, in general, the voltage source is not necessarily part of the device. However, in various embodiments, the device may include the voltage source.

In order to connect the capacitive element to the voltage source or to transfer the amount of charge from the capacitive element to the further capacitive element, the circuit can have, for example, corresponding switching elements and a controller for controlling the switching elements. In various configurations, the controller can also be part of the evaluation unit.

In particular, the evaluation unit can contain a microcontroller.

According to at least one embodiment, the evaluation unit includes an analog-to-digital converter, ADC, which can be connected to the further capacitive element in order to To determine the measured value, in particular to determine a voltage drop across the further capacitive element as the measured value.

Further embodiments of the device according to the invention follow directly from the different embodiments of the method according to the invention for error detection and the method according to the invention for detecting a user input and vice versa. In particular, a device according to the invention can be set up to carry out a method according to the invention or it carries out such a method.

According to a further aspect of the invention, a user input device, also referred to as a user input interface, is specified, in particular a user input device for use in a motor vehicle interior of a motor vehicle. The user input device includes a capacitive element arranged and adapted to be touched by a user. The user input device contains a device according to the invention.

According to a further aspect of the invention, a motor vehicle with a user input device according to the invention is also specified.

According to a further aspect of the invention, a computer program product with instructions is provided. When the commands are executed by a device according to the invention, in particular by the evaluation unit of the device according to the invention, the commands cause the device to carry out a method according to the invention for error detection or a method according to the invention for detecting a touch of a capacitive element.

The computer program can be configured as a computer program with the commands, for example. The computer program product can also be designed as a computer-readable storage medium with a computer program that contains the instructions.

Further features of the invention result from the claims, the figures and the description of the figures. The features and feature combinations mentioned above in the description and the features and feature combinations mentioned below in the description of the figures and/or shown in the figures can be used not only in the combination specified in each case, but also in other combinations be encompassed by the invention. In particular, the invention also includes versions and combinations of features that do not have all the features of an originally formulated claim. The invention also encompasses designs and combinations of features that go beyond or deviate from the combinations of features set out in the back references of the claims.

In the figures show:

1a shows a schematic representation of an exemplary embodiment of a device according to the invention in an initialization state;

FIG. 1b shows a schematic representation of the device from FIG. 1a in an intermediate state; FIG.

1c shows a schematic representation of the device from FIGS. 1b and 1c in a charging state;

1d shows a schematic representation of the device from FIGS. 1a to 1c in a transmission state;

1e shows a schematic representation of the device from FIGS. 1a to 1d in a readout state;

2 shows a flow chart of a first part of an exemplary embodiment of a method according to the invention;

3 shows a flow chart of a second part of an exemplary embodiment of a method according to the invention;

4 schematically different threshold values in an exemplary embodiment of a method according to the invention;

5a shows a schematic representation of a further exemplary embodiment of a device according to the invention in an initialization state; FIG. 5b shows a schematic representation of the device from FIG. 5a in an intermediate state; FIG.

5c shows a schematic representation of the device from FIGS. 5b and 5c in a charging state;

5d shows a schematic representation of the device from FIGS. 5a to 5c in a transmission state;

FIG. 5e shows a schematic representation of the device from FIGS. 5a to 5d in a read-out state; FIG.

6a shows a schematic representation of a further exemplary embodiment of a device according to the invention in an initialization state;

FIG. 6b shows a schematic representation of the device from FIG. 6a in an intermediate state; FIG.

6c shows a schematic representation of the device from FIGS. 6b and 6c in a charging state;

FIG. 6d shows a schematic representation of the device from FIGS. 6a to 6c in a transmission state; FIG.

FIG. 6e shows a schematic representation of the device from FIGS. 6a to 6d in a read-out state;

7a shows a schematic representation of a further exemplary embodiment of a device according to the invention in an initialization state;

FIG. 7b shows a schematic representation of the device from FIG. 7a in an intermediate state; FIG.

7c shows a schematic representation of the device from FIGS. 7b and 7c in a charging state; FIG. 7d shows a schematic representation of the device from FIGS. 7a to 7c in a transmission state; FIG. and

FIG. 7e shows a schematic representation of the device from FIGS. 7a to 7d in a read-out state.

1a to 1e show an exemplary embodiment of a device 2 according to the invention, which is part of a user input device 1, for example, for use in the interior of a motor vehicle (not shown). 1 a to 1 e represent different states of the device 2 corresponding to different sections of measurement cycles in a method according to the invention.

The user input device 1 has a capacitive element 3 which is arranged and set up to be touched by a user. The capacitive element 3 can be designed, for example, as a touch-sensitive foil or touch-sensitive sensor plate. The user can, for example, touch or approach a surface of the capacitive element 3 with a finger in order to provide user input. When the user approaches or touches the capacitive element 3, its capacitance changes. The device 2 is able to determine the capacitance or the change in capacitance of the capacitive element 3 and based thereon infer the presence of the user input.

The capacitance of the capacitive element 3 can be understood as an intrinsic capacitance compared to a ground potential. Therefore, the capacitive element 3 is shown in Figures 1a to 1e as a capacitor whose first connection is connected to a reference potential connection 9, in particular a ground connection.

The device 2 has a connection 4 in order to connect the capacitive element 3, in particular a second connection of the capacitive element 3, to the device 2, as well as a further capacitive element 5, which can be designed as a capacitor, for example.

The second connection of the capacitive element 3 is connected to a first connection of the further capacitive element 5 . The second connection of the capacitive element 3 is in particular directly connected to the sensor plate or the touch-sensitive chen foil or the like connected or formed thereby. A second connection of the further capacitive element 5 is connected to a first connection 7 of an evaluation unit 6 of the device 2 . A second connection 8 of the evaluation unit 6 is connected to the second connection of the capacitive element and to the first connection of the further capacitive element 5 . The evaluation unit 6 can contain, for example, a microcontroller or another integrated circuit.

The device 2 also has a circuit which is not shown separately in FIGS. 1a to 1e. The circuit includes a controller and several switching elements that can be controlled by the controller. The controller can also be part of the evaluation unit 6 . The switching elements are arranged and set up to be controlled by the controller to connect the connections 7 and 8 of the evaluation unit 6 to the reference potential connection 9 or to separate them from it, depending on the current state of the device 2 . Using the switching elements, the controller can also connect a voltage source 10, which can be part of the device 2 or the user input device 1 or can be provided externally to them, for example, to the second connection 8 of the evaluation unit 6 or disconnect the connection, depending on the state of the device 2

The evaluation unit 6 also has an analog/digital converter, ADC, 11 which can be connected to the second connection 8 . In particular, the switching circuit can connect or disconnect the ADC 11 to the second terminal 8 depending on the state of the device 2 .

1a to 1e show a situation in which there is no error. In Fig. 5a to Fig. 5e, the device of Fig. 1a to Fig. 1e is shown again in the same states, with an error being present here which is caused by a partial or complete interruption, for example a line break, in an electrical connecting line between the capacitive element 3 and the further capacitive element 5 is given. The interruption or partial interruption can in particular lie between the connection 4 and the capacitive element 3 or between the connection 4 and the further capacitive element 5.

Such an error, which can also be referred to as an open circuit, "open load" or "open circuit", can be traced back, for example, to an incorrectly connected plug connection, a defect in the sensor plate or the touch-sensitive film or the like. 6a to 6e show the device of FIGS Element 5 is given to the reference potential terminal 9. In particular, there is therefore a short circuit to ground.

7a to 7e show the device of FIGS Element 5 is provided with a voltage supply connection 17 . The voltage supply connection 17 can in particular correspond to an output of the voltage source 10 or be connected to it. In particular, there is a short circuit to the supply voltage.

When carrying out a method according to the invention, various states S0, S1, S2, S3, S4 of the device 2, as shown in FIGS. 1a to 1e and 5a to 7e, are partly cyclically or repeated run through, as shown by way of example in FIG. SO designates an initialization state of the device 2 during an initialization section of the method and S4 designates a readout state of the device 2 during a readout section of the method.

The states S1 to S3 form a measurement cycle, with a large number of successive measurement cycles being carried out to carry out the method. As can be seen from Fig. 2, to determine the capacitance of the capacitive element 3 or to detect the user input, the device 2 is first brought into the initialization state SO, then the plurality of measurement cycles are carried out and again after that the device 2 is in the Brought readout state S4. The process outlined in FIG. 2 can also be referred to as a measurement process, in which case the measurement process can also be carried out repeatedly during operation of the device 2 or the user input device 1 in order to implement permanent monitoring of the capacitive element 3 with regard to a touch by the user.

In one embodiment of the method as shown in FIG. 2, each measurement cycle includes an intermediate section, a subsequent charging section, a subsequent further intermediate section and a subsequent transmission end- cut. Accordingly, during a measurement cycle, the device 2 is transferred from an intermediate state denoted S1 to a charging state denoted S2, which is again followed by the intermediate state S1, followed by a transfer state denoted S3. After the end of the measurement cycle, the evaluation unit 6 checks whether a predetermined number of measurement cycles per measurement process has been reached. If this is the case, the device 2 is brought into the readout state S4, otherwise the next measurement cycle follows.

In the SO state, the controller uses the circuit to connect the first connection 7 and the second connection 8 to the reference potential connection 9. The first and the second connection of the capacitive element 3 and the first and the second connection of the further capacitive element 5 are each connected to the reference potential connection 9 . Accordingly, both the capacitive element 3 and the further capacitive element 5 are discharged during the initialization state SO. In the subsequent first intermediate section, the device 2 is brought into the intermediate state S1, which can also be referred to as the switching state or switching state. Here the connections 7 and 8 of the evaluation unit 6 are separated from the reference potential connection 9 . The device 2 remains in the intermediate state S1 during the intermediate section for an intermediate duration which is, for example, less than 1 ps, for example between 0.1 ps and 1 ps.

Thereafter, the controller transfers the device 2 to the charge state S2 by means of the switching circuit. In comparison to the intermediate state S1, here the second connection 8 of the evaluation unit 6 is connected to the voltage source 10 in order to charge the capacitive element 3 in this way. By setting the first connection 7 internally to a high impedance, for example, the amount of charge on the further capacitive element 5 does not change. The state of charge S2 is maintained for a specified charging period, which can be in the range from 1 ps to 10 ps, for example. Thereafter, the device 2 is brought back into the intermediate state S1 during a further intermediate section. A further intermediate duration of the further intermediate section can be equal to the intermediate duration of the intermediate section, for example.

During a subsequent transmission section, the device 2 is brought into the transmission state S3, which can also be referred to as the transfer state, by the control of the switching circuit. Here the second connection 8 of the evaluation unit 6 is now set to a high impedance and the first connection 7 is connected to the reference potential connection 9 . This allows a charge balance between the capacitive element 3 and the further capacitive element 5 take place. The capacitance of the further capacitive element 5 is chosen to be many times higher than the maximum capacitance of the further capacitive element 3, so that a charge quantity determined by the two capacitances is effectively transferred from the capacitive element 3 to the further capacitive element 5.

A transmission duration of the transmission section can be, for example, in a range from 0.5 ps to 5 ps or in a range from 0.5 ps to 2 ps or the like. A readout duration of the readout period can be, for example, in a range from 0.5 to 5 ps or in a range from 0.5 ps to 2 ps.

The states S1, S2, S1, S3 are repeated cyclically in this order, as indicated in FIG. 2, until a predetermined total number of measurement cycles has been run through, for example 300 to 500 measurement cycles. After the total number of measurement cycles, a total amount of charge was transferred from the capacitive element 3 to the further capacitive element 5 in the respective transfer sections. This total amount of charge is now read out by means of the evaluation unit 6 in the subsequent readout section. For this purpose, the device 2 is brought into the readout state S4 by means of the controller and the circuit. For this purpose, the first connection 7 of the evaluation unit 6 remains connected to the reference potential connection 9 and the second connection 8 of the evaluation unit 6 is connected to the ADC 11 in order to measure the voltage between connection 4 of the device 2 and the reference potential connection 9 and thus to determine a measured value , which reflects the total amount of charge.

After the readout section, the evaluation unit 6 can compare the measured value determined in this way with two or more specified threshold values in order to determine whether there is an error and, if so, to assign an error type to the error.

FIG. 3 shows a flow chart of a further part of a method according to the invention, which begins with the readout state S4 and is used for error detection and error classification.

4 shows a number of threshold values for the measured value as horizontal lines, with the ordinate axis corresponding to the measured value. In particular, three threshold values 12a, 12b, 12c are provided, which correspond to the different error types. If the measured value is less than the threshold value 12a, a short circuit to the reference potential 9 can be assumed. If the reading is less than the threshold value 12b, but greater than the threshold value 12a, it is an open circuit. If the measured value is greater than the threshold value 12c, there is a short circuit to the voltage supply connection 17. The theoretical upper limit 16 for the measured value is also shown. The upper limit 16 can correspond to the maximum value of the ADC 11, for example.

In step S5 of the method in FIG. 3, the evaluation unit 6 compares the measured value with the threshold value 12a. If the measured value is less than the threshold value 12a, the method continues in step S6, otherwise in step S9. In step S6, a first counter value relating to the error type of the short circuit to the reference potential connection 9 is increased by one increment since the measured value was less than the corresponding threshold value 12a. In step S7, the evaluation unit 6 then compares the current first counter value with a corresponding first error confirmation value. If the first counter value is greater than the first error confirmation value, the error is confirmed in step S8. In other words, the error is then deemed to have been detected. Accordingly, an error bit can be set in a corresponding error register, for example. The method can then be continued with the next measurement cycle and step S1 as described with reference to FIG. 2 . Alternatively, the user input device 1 can also be deactivated or the method can no longer be continued if the error bit was set in step S8.

If it is not determined in step S5 that the measured value is less than the threshold value 12a, the measured value is compared with the threshold value 12b in step S9. If the measured value is less than the threshold value 12b, the method is continued with step S10, otherwise with step S13. In step S10, a second counter value is increased by one increment since, according to the comparison from step S9, there is an open circuit. In step S11, the second counter value can be compared with a corresponding second error confirmation value, analogously to that described with regard to step S7. If the second counter value is greater than the second error confirmation value, a corresponding further error bit can be set in step S12, which confirms the presence of the open circuit. The method can then be continued with the next measurement cycle or the user input device 1 can be deactivated as described or the like.

If it is established in step S9 that the measured value is not less than the threshold value 12b, then in step S13 the measured value is compared with the threshold value 12c. If the measured value is greater than the threshold value 12c, the method continues with step S14, otherwise with step S17. In step S14, as described with reference to step S6 or S10, a third counter value is increased by one increment in order to take account of the determination of a short circuit to the voltage supply connection 17 based on the comparison from step S13. In step S15, the third counter value is compared with a third error confirmation value, analogously to that described with regard to step S7 and step S11. If the third counter value is greater than the third error confirmation value, a corresponding error bit is set in step S16. The next measurement cycle can then be carried out or the user input device 1 can be deactivated accordingly.

If it is determined in step S13 that the measured value is less than the threshold value 12c, then the measured value is in particular between the threshold value 12b and the threshold value 12c. This is the range that can be expected for the device 2 to operate correctly. Accordingly, it is determined in step S17 that there is no error.

For example, by comparing the measured value with a further threshold value 13, the evaluation unit 6 can determine whether or not the user has touched it. If the measured value is greater than the further threshold value 13, it can be assumed that there has been contact; if the measured value is lower than the further threshold value 13, then there is no contact. However, a hysteresis can also be taken into account by providing a threshold value 14 that is slightly smaller than the threshold value 13. A touch can then be detected, for example, if the measured value is greater than the threshold value 13 and as long as it is greater than the threshold 14. The thresholds 13 and 14 are respectively between the threshold 12b and the threshold 12c. In addition, a baseline or reference line 15 is drawn in, which lies between the threshold value 12b and the threshold value 13, in particular between the threshold value 12b and the threshold value 14. The reference line 15 can be tracked, for example, so that the detection is based on a change in the measured value with respect to the Reference line 15 can be detected.

In various embodiments, in addition to the counter values for the errors, a respective further counter value can also be provided, which is each increased by an increment if the corresponding error type is not determined at the end of the corresponding measurement cycle. If, after a measurement cycle according to the method described, it is determined that there is no error, all other counters relating to the healing can be increased by 1 increment. It can also be a be implemented individual approach by making a specific decision for each type of error, whether the further error memory is incremented regarding the healing of the respective error type. A corresponding healing confirmation limit value can then also be provided for each of the counters and the corresponding error bit can be reset, for example, when this is reached. The error is then no longer active. However, it can be stored in a memory element that the error was present in order to ensure appropriate documentation.

As described in particular with reference to the figures, the invention makes it possible to detect and classify different types of faults in a device for detecting touching of a capacitive element, in particular based on a Q-Charge method.

In this way, the requirement for electrical fault detection can be comprehensively met, particularly for applications in motor vehicles. A reliable and differentiated fault analysis according to the invention is advantageous especially for user input devices that are linked to safety-related functions, for example functions for warning of hazards, for lighting control, for a parking brake or for locking and unlocking the doors of the vehicle. The invention can of course also be applied to a number of capacitive elements or a number of user input devices, ie a number of touch-sensitive elements, in particular in the vehicle. It is then advantageous to provide each user input device with individual threshold values in order to take sufficient account of differences in the specific design, tolerance ranges or line capacities.

Claims

22 patent claims

1 . Method for error detection when operating a device for detecting a touch of a capacitive element (3), wherein during each measuring cycle of a plurality of consecutive measuring cycles the capacitive element (3) is charged and then within the same measuring cycle a charge quantity is transferred from the capacitive element (3) to another capacitive element (5) is transmitted; after the plurality of measurement cycles, a measured value relating to a total amount of charge transferred to the further capacitive element (5) during the plurality of measurement cycles is determined; and characterized in that it is checked whether the measured value is less than or equal to a predetermined first threshold value and whether the measured value is greater than or equal to a predetermined second threshold value; depending on a result of the test, the presence of an error is determined and an error type of the error is determined.

2. The method according to claim 1, characterized in that the measured value is compared with the first threshold value; the presence of the error is determined and the error is assigned to a first error type if the measured value according to the comparison with the first threshold value is less than or equal to the first threshold value.

3. The method as claimed in claim 2, characterized in that the measured value is compared with the second threshold value if the measured value is greater than the first threshold value; the presence of the error is determined and the error is assigned to a second error type if the measured value is greater than or equal to the second threshold value according to the comparison with the second threshold value.

4. The method according to claim 2, characterized in that the measured value is compared with a third threshold value if the measured value is greater than the first threshold value; the presence of the error is determined and the error is assigned to a third error type if the measured value is less than or equal to the third threshold value according to the comparison with the third threshold value.

5. The method according to claim 4, characterized in that the measured value is compared with the second threshold value if the measured value is greater than the third threshold value; the presence of the error is determined and the error is assigned to a second error type if the measured value is greater than or equal to the second threshold value according to the comparison with the second threshold value.

6. The method according to any one of claims 4 or 5, characterized in that the first type of error corresponds to a short circuit of an electrical connecting line between the capacitive element (3) and the further capacitive element (5) with a reference potential connection (9); and/or the third type of error corresponds to a break or a partial break in the electrical connection line between the capacitive element (3) and the further capacitive element (5).

7. The method according to any one of claims 3 or 5, characterized in that the second type of error corresponds to a short circuit in an electrical connection line between the capacitive element (3) and the further capacitive element (5) with a voltage supply connection (17).

8. The method according to any one of the preceding claims, characterized in that each of the measurement cycles includes a charging portion, wherein the charging of the capacitive element takes place during the charging portion; each of the measurement cycles includes a transfer section, the amount of charge being transferred from the capacitive element (3) to the further capacitive element (5) during the transfer section.

A method according to claim 8, characterized in that each of the measurement cycles includes an intermediate portion between the charging portion and the transmitting portion, during which intermediate portion the capacitive element (3) is neither charged nor discharged; and/or each of the measurement cycles includes a further intermediate section before the charging section or after the transmission section, during which further intermediate section the capacitive element (3) is neither charged nor discharged.

10. A method for detecting a user input, which includes a touch of a capacitive element (3) by a user, characterized in that a method according to any one of the preceding claims is carried out; the user input or the touch is determined depending on the measured value.

11 . Method according to Claim 10, characterized in that the measured value is compared with a further threshold value which is greater than the first threshold value and smaller than the second threshold value; and the user input or the touch is detected when the measured value according to the comparison with the further threshold is greater than the further threshold.

12. Device (2) for detecting a touch of a capacitive element (3), the device (2) having 25, a terminal (4) to connect the capacitive element (3) to the device (2); a circuit configured to, during each measurement cycle of a plurality of consecutive measurement cycles

- connecting the capacitive element (3) to a voltage source (10) in order to charge the capacitive element (3); and

- subsequently transferring a quantity of charge from the capacitive element (3) to a further capacitive element (5) of the device (2); and an evaluation unit (6) which is set up to determine, after the plurality of measurement cycles, a measured value relating to a total amount of charge transferred to the further capacitive element (5) overall during the plurality of measurement cycles; characterized in that the evaluation unit (6) is set up to check whether the measured value is less than or equal to a predetermined first threshold value and whether the measured value is greater than or equal to a predetermined second threshold value; to determine the presence of an error depending on a result of the check and to determine an error type of the error. User input device (1) comprising a capacitive element (3) arranged to be touched by a user, characterized in that the user input device (1) includes a device (2) according to claim 12. Motor vehicle with a user input device (1) according to claim 13. Computer program product with instructions which, when executed by a device (2) according to claim 12, cause the device (2) to carry out a method according to one of claims 1 to 11.