METHOD AND DEVICE FOR PROXIMITY DETECTION

Description

[0001] The present invention relates to a method and a device for proximity detection. In particular, the invention relates to a method and a device for use in vehicles to detect an activation action for a function on the vehicle by detecting the approach of a person or a body part of the person to a sensor element of the arrangement.

[0002] It is known from the prior art that a sensor element having a sensor electrode can provide a variable capacitance that is sensitive to changes in the sensor element's environment. Detecting the variable capacitance makes it possible to detect changes in the sensor element's environment. In vehicles, such capacitive sensing can be used to detect approaches and / or gestures, thus activating vehicle functions.

[0003] Capacitive detection is based on the sensor element being evaluated by means of charge transfer. DE 10 2019 133 913 A1 discloses a generic device and an associated method. The device disclosed therein for detecting an activation action has at least one capacitive sensor element for detecting an approach. The sensor element is repeatedly subjected to a voltage and charged according to its capacitance. Subsequently, the charge accumulated on the sensor element is transferred to a storage element. For this purpose, a rectifier arrangement rectifies the sensor voltage between an electrical storage arrangement and the sensor element. An evaluation is carried out based on the amount of charge stored on the storage arrangement after one or more charge transfers, whereby the amount of charge is checked to determine whether this is characteristic of an approach.

[0004] One problem with known methods and devices is that environmental conditions can complicate capacitive detection and analysis. In particular, moisture, e.g., in the form of water films in the area of ​​the sensor elements, impairs detection, especially if these water films have electrical ground contact.

[0005] From document DE 10 2019 133 913 A1, an arrangement with a sensor element for detecting a change in proximity by means of an activation means in an environment of the sensor element is known. A control arrangement serves to generate an electrical control signal for carrying out repeated charge transfers at the sensor element and for capacitive sensor evaluation. A transmission arrangement serves to provide an electrical sensor signal based on the repeated charge transfers and the control signal. A rectifier arrangement for rectifying the electrical sensor signal is connected between the electrical storage arrangement and the transmission arrangement. The arrangement is suitable for a vehicle for detecting an activation process of a function on the vehicle. The arrangement performs a detection based on the evaluation to output an activation signal for activating the function on the vehicle when the charge quantity exceeds a limit value.

[0006] The object of the invention is to provide a method and a device which allow reliable detection and evaluation even under problematic environmental conditions.

[0007] This object is achieved by a method and a device having the features of the independent claims.

[0008] The invention is based on the finding that detection can be more robust against environmental conditions if it detects both the reactance of a sensor element and its resistance. In the known devices, a capacitive sensor is charged and discharged with a changing potential such that the resulting sensor signal corresponds to an alternating voltage signal, and its waveform in particular resembles an oscillation. During detection, the sensor signal is then demodulated such that the main focus is on detecting the reactance of the sensor element, while other components of the impedance, i.e. the reactance, are not evaluated. According to the invention, the detection, in particular the demodulation of the sensor signal, is adapted such that reactance and components of the resistance are detected together.For this purpose, the invention uses a clock signal to time the rectification of the voltage signal detected by the sensor means and the storage of the charge contained in the rectified signal so that the additive amplitudes of both the reactance and the resistance contained in the signal are measured. The method used according to the invention is similar to the concept of quadrature amplitude modulation (QAM) and the associated demodulation. In QAM, a carrier is used twice, but with a 90° phase shift, so that two carriers are initially created. A signal is modulated onto each carrier using multiplicative mixing. The two modulated signals are then added to obtain the transmitted signal. During demodulation, the signals are separated with a phase position identical to that of the transmitter.The invention exploits the fact that the actual modulation occurs in the sensor device, where the impedance of the sensor device (in particular, capacitive reactance and resistance) causes the modulation. This applies when the sensor device is supplied with an alternating voltage. The modulation thus occurs readily due to the resistive and capacitive components of the impedance in the sensor device. In the circuit of DE 10 2019 133 913 A1, which is also suitable for implementing the invention, this modulation also occurs in principle.

[0009] According to the invention, demodulation requires special timing of the rectification in order to feed the sensor signal, with regard to phase and duty cycle, for integration and storage only in selected sections of the sensor signal. While in the prior art, switching and timing are usually carried out to detect the capacitive reactance, according to the invention the phase and duty cycle are changed to detect resistance and reactance. This is achieved according to the invention by selecting a value of 0.25 to 0.6 for the duty cycle of the clock signal, based on the period of the sensor signal. The phase is also selected such that, based on the sensor signal, at least two quadrants are included in the rectification and storage and at least one zero crossing (or inflection point) of the sensor signal is included.

[0010] Quadrants of the signal are understood to be a quarter of a full period, beginning with a zero crossing (or inflection point) of the sensor signal (beginning of the first quadrant), a first positive maximum (end of the first quadrant and beginning of the second quadrant), a second zero crossing (end of the second quadrant and beginning of the third quadrant), a (negative) minimum (end of the third quadrant and beginning of the fourth quadrant), and ending with the renewed zero crossing (end of the fourth quadrant). A negative half-wave of the sensor signal extends over the third and fourth quadrants, while the positive half-wave extends over the first and second quadrants. Due to the resistive and capacitive components of the signal, the quadrants contain different information in different sections. In the state of the art, for example,The third and fourth quadrants, i.e., the negative half-waves, are rectified and integrated to measure the reactance. According to the invention, however, a signal section with a zero crossing is used to always include a signal component of the resistance. The clock signal is synchronized with the sensor signal (which in turn is usually synchronized with the control signal for the sensor).

[0011] Coherent rectifiers are particularly suitable as rectifiers, as they not only respond to the amplitude of the input signal but also take its phase into account. An input signal is compared with a reference signal.

[0012] According to the invention, a change in the duty cycle of the clock signal occurs periodically or as a function of the evaluation signal.

[0013] For example, both reactance and resistance are repeatedly measured, alternating with measurements of other components of reactance and resistance. In this way, a basic measurement of reactance can be achieved, as in the prior art and by rectifying the negative half-wave (third and fourth quadrants of the sensor signal). However, the duty cycle and / or phase of the clock signal are changed at predetermined intervals in order to simultaneously measure a component of the resistance. Thus, the invention makes it possible to detect differences in the signals between the two measurement methods when the environment of the capacitive sensor element changes, e.g., when it starts to rain.

[0014] In a preferred embodiment of the invention, the duty cycle is 0.5 and the phase of the clock signal is selected to be -45°, so that the third quadrant (i.e., the first half of the negative half-wave) and one half each of the second and fourth quadrants are included in the rectification of the sensor signal. The resulting demodulation then comprises a total of one-quarter of the positive half-wave and three-quarters of the negative half-wave.

[0015] It has been shown that this selection allows a robust evaluation of an approach to the sensor electrode, even if it is exposed to a liquid coating (even if the liquid coating is grounded).

[0016] The invention will now be explained in more detail with reference to the accompanying drawing. Fig. 1 shows a circuit arrangement according to the prior art which is suitable for carrying out the method according to the invention; Fig. 2 shows a detailed view of components from Fig. 1 ; Fig. 3 shows a schematic representation of the operating principle of the invention; Fig. 4a shows schematically a tuning of the clock signal for the rectifier according to the prior art; Fig. 4b schematically shows a tuning of the clock signal for the rectifier according to an embodiment of the invention; Fig. 5 shows schematically the comparison of measurement signals under the same conditions according to the prior art on the one hand and according to the invention on the other hand;

[0017] In Fig. 1 A device 10 according to the prior art is shown, which is suitable for detecting an approach according to the method according to the invention. The device 10 has at least one sensor element 20 for detecting a change in an environment of the sensor element 20. In reality, the sensor element 20 is formed by a capacitive electrode, which, for example, .arranged in the door handle of a vehicle or in the rear bumper of a vehicle (kick sensor). According to the invention, the evaluation / demodulation is sensitive to both the reactance and the resistance of the sensor element 20. However, with regard to the illustrated design, there is no structural difference in the components of the sensor element 20 and the other components in the illustrated circuit compared to the prior art, since the implementation of the invention lies in a modified control and demodulation, i.e., a different operation of the components.

[0018] With respect to the environment and / or a ground potential 21, the sensor element 20 has a capacitance (hereinafter also referred to as sensor capacitance CS) and thus also a reactance essentially determined by the capacitance. In addition, the sensor element 20 has a resistance. By generating an electrical potential (by means of an electrical control described below) at the sensor element 20, an electrical field is generated in its environment. The sensor capacitance CS is influenced by the change in the environment, as is its resistance. An evaluation of the capacitance CS according to the prior art is carried out by evaluating the amount of charge stored in the sensor element 20 and allows conclusions to be drawn about the change in its environment.Carrying out charge transfers from and to the sensor element 20 is suitable for providing a sensor signal based on the charge transfers (such as the amount of charge transferred and / or the current and / or voltage that can be detected thereby), which sensor signal can be evaluated to determine the variable capacitance CS.

[0019] A control / evaluation circuit 100 is used to implement the electrical control. The control / evaluation circuit 100 is electrically coupled to the sensor element 20 via a control path KP for electrically controlling the sensor element 20. The electrical control causes a (forced) charging and discharging of the sensor element 20. Detection is effected by the control / evaluation circuit 100 applying a potential to the sensor element 20 in order to charge the sensor element 20. This potential is a changing potential, so that an electrical voltage is generated at the sensor element 20, e.g., as a periodic and / or sinusoidal voltage. An evaluation arrangement 200 is provided for evaluating the sensor element 20, which allows repeated determination of the variable capacitance.

[0020] It is optionally provided that at least one shield element 160 is provided, which is arranged adjacent to (and thus within the effective range of) the sensor element 20 for shielding the sensor element 20. To enable shielding by the shield element 160, a shield control arrangement 150 with a connection 150.A for the shield element 160 is provided. The shield control arrangement 150 can be electrically connected to the control path KP and thus also to the shield element 160 via a shield control input 150.B for providing the (previously described) electrical control of the control / evaluation circuit 100 for the shield element 160. Thus, the shield control arrangement 150 can provide the same electrical control for the shield element 160 that is also used for the sensor element 20.

[0021] The control / evaluation circuit 100 has a signal generator arrangement 130, which is electrically coupled to the sensor element 20 for electrically controlling the sensor element 20 in order to repeatedly generate an electrical control signal for charging the sensor element 20. In this embodiment, the control / evaluation circuit 100 has a filter arrangement 140, e.g., a low-pass filter. This is connected downstream of the signal generator arrangement 130 in order to output the control signal for electrically controlling the sensor element 20, filtered, via the control path KP to the sensor driver circuit 170. In this way, the control signal can be shaped with a specific operating frequency. This advantageously allows EMC (electromagnetic compatibility) specifications to be implemented during the operation of the device 10. The active filtering is preferably implemented by an operational amplifier 140.1 and by filter elements 140.2 such as at least one capacitor and / or at least one resistor and / or at least one coil.

[0022] The control signal generated by the signal generator arrangement 130 is filtered and applied to terminal 170.C. The sensor driver circuit 170 controls the sensor element 20 based on the control signal. Thus, based on the control signal, a charge transfer (charging and / or discharging) is initiated at the sensor element 20 (possibly also to the further sensor element 20' and / or the shield element 160). The temporal progression of this charge transfer can be influenced by shaping the electrical signal. For this purpose, the signal generator arrangement 130 comprises, for example, a digital-to-analog converter 130.1.

[0023] In order to interrupt any charge transfer to the sensor element 20 and, for example, to charge at least one further sensor element 20', the switching element 180 can be opened in a clocked manner and then closed again. The sensor driver circuit 170 has an amplifier and / or a voltage follower and / or a voltage multiplier to replicate an electrical potential present at terminal 170.C on the sensor element 20. For this purpose, the sensor driver circuit 170 has an operational amplifier 170.1 and at least one amplification means 170.2. A further switching element 180 can, for example, be coupled in the path between the terminal 170.A and the further sensor element 20' and, for example, be switched alternately with the switching element 180.

[0024] The sensor driver circuit 170 effects the repeated charge transfers to the sensor element 20 via the operational amplifier 170.1. For this evaluation of the sensor element 20, the sensor driver circuit 170 has at least one amplification means 170.2, which is electrically coupled to the evaluation arrangement 200 (and also to the sensor element 20). It is shown that the amplification means 170.2 electrically couples an output of the operational amplifier 170.1 to a (particularly inverting) first input of the operational amplifier 170.1, so that the amplification means 170.2 forms a negative feedback for the operational amplifier 170.1. The negative feedback enables the charge transfers to be controlled by the control signal when the control signal is applied to the other (particularly non-inverting) second input of the operational amplifier 170.1. If the first input is directly connected to the terminal 170.A is electrically connected, as in . Fig. 1 As shown, in this way, the sensor driver circuit 170 provides a voltage follower for the sensor element 20, so that the voltage at the (particularly low-impedance) terminal 170.A follows the control signal at the (particularly high-impedance) terminal 170.C. This corresponds to the control of the charge transfers at the terminal 170.A by the control signal, and thus to a (particularly low-impedance) sensor supply. The sensor signal is provided at tap 170.B of the amplifier arrangement comprising the operational amplifier 170.1 and the amplification means 170.2. The amplification means 170.2 has at least one or two filter elements, in this example a capacitance C and a resistor R. This arrangement forms the amplification means 170.2, which generates an electrical voltage proportional to the sensor capacitance CS. The sensor signal is then (particularly proportional) dependent on the voltage U1 at the first terminal 170.A of the sensor driver circuit 170 (or at the first input of the operational amplifier 170.1), amplified by an amplification factor.

[0025] For evaluating the reactance and resistance of sensor element 20, the invention provides for charge transfer from sensor element 20 (or the further sensor element 20') via sensor driver circuit 170 to evaluation arrangement 200. The sensor element 20 is repeatedly charged and discharged via the first terminal 170.A of sensor driver circuit 170 by means of charge transfers. Depending on the charge transfers, an electrical sensor signal is output via the second terminal 170.B of sensor driver circuit 170. Depending on the amount of charge transferred, a storage arrangement 250, preferably an integrator 250, of evaluation arrangement 200 is charged. These repeated charges and discharges are controlled by the control signal (due to a periodically changing voltage amplitude of the control signal).

[0026] Component 300 of control / evaluation circuit 100 is coupled via a terminal 250.A to the memory device 250 of the evaluation device 200 in order to evaluate the electrical charge accumulated by the memory device 250 after one or more measurements to determine a value characteristic of the state of the sensor element. From this charge state, an evaluation signal is generated, which is sent to a downstream device, e.g. . a central control unit of a vehicle.

[0027] It is optional to perform electrical filtering of the sensor signal before rectification. For this purpose, an evaluation filter arrangement 210 can be used to filter the electrical sensor signal (such as bandpass filtering). This makes it possible to filter out interfering emissions from the environment of the sensor element 20 (EMC filtering of emissions). For this purpose, the evaluation filter arrangement 210 comprises, for example, a complex resistor and additional filter elements.

[0028] The Fig. 1 Block 220 shown is a rectifier arrangement. The described rectification can be a "coherent" rectification by the at least one rectifier. This means that the at least one rectifier forwards the sensor signal from the evaluation filter arrangement 210 to the memory arrangement 250 according to a predetermined clock signal.

[0029] In Fig. 2 Details of the evaluation device 200 are shown, namely an evaluation filter arrangement 210, a rectifier arrangement 220, and a memory arrangement 250 with further details. The evaluation filter arrangement 210 serves to filter the sensor signal provided by the sensor driver circuit 170. Its filter elements can each be designed, for example, as a resistor, coil, and / or capacitor, and thus as an RC and / or RL element (and / or as an RLC element). By interconnecting and designing the filter elements 210.1, a low-pass and high-pass behavior of the evaluation filter arrangement 210 can be set, thus providing a bandpass filter. This bandpass filter is advantageously adapted to a frequency of the electrical control, in particular an operating frequency of the control signal, with regard to its passband and / or center frequency.Through serial connection to a virtual zero point 250.B of the storage device 250, the filtered sensor signal can then be forwarded as a current signal to the storage device 250. In this way, a charge transfer to and thus charging of the storage device 250 can occur.

[0030] The rectifier arrangement 220 comprises at least one controllable rectifier 220.1, preferably in the form of a synchronous rectifier or the like. The clock rate with which the rectifier arrangement is controlled can be synchronized with the signal generator arrangement 130.

[0031] While the device is in the Figuren 1 and 2 As is generally known (e.g. from DE 10 2019 133 913 A1), the use and parameterization of the device according to the invention is responsible for a significantly more robust detection of approaches, even under critical environmental conditions.

[0032] According to the invention, the clock signal for rectifying the sensor signal is selected with regard to its phase and duty cycle such that both reactance and resistance signal components are included in the rectified signal forwarded to the memory arrangement.

[0033] In Fig. 3 The concept of the detection according to the invention is shown schematically. The principle corresponds to the principle of quadrature amplitude modulation. Two carrier signals IPH and QPH are phase-shifted from each other (corresponding to a sine and the associated cosine). Signals I and Q are modulated onto the respective carriers, corresponding to the components of resistance and reactance, respectively. The signals are added, resulting in a modulated overall signal QAM. A clock signal CCLK provides a synchronous phase-shifted rectifier clock, according to which the QAM signal is rectified to the CR_QAM signal. A smoothing filter FLTR then supplies the QADM signal, which is optimized for maximum swing when the resistive and capacitive components of the sensor signal increase simultaneously.

[0034] Due to the capacitive and resistive components present in the sensor element, Fig. 3 processes represented by carrier and signal modulation without any further structural changes. The timing and phase of the evaluation, i.e., demodulation, are crucial for simultaneously evaluating the resistive and capacitive components present in the signal. The phase of the rectification and the duty cycle of the signal evaluation are crucial here; these are selected according to the invention so that both the resistance and the reactance are incorporated into the resulting signal for charging a storage device.

[0035] The Fig. 4a shows a timing diagram for an evaluation according to the prior art, wherein a signal 510 is rectified by the clock signal 500. The illustration shows the synchronous coordination of the timing and the sensor signal 510. In this example, the negative half-wave of the signal 510 is subjected to rectification, controlled by the clock signal 500, and then passed to a storage device, which is charged as a function of the signal from the sensor element. In this timing, the different charging of the storage device varies primarily as a function of the reactance of the sensor means. Therefore, if the capacitance changes, this causes a change in the charge accumulated in the storage device.

[0036] In Fig. 4b In contrast, a clocking system according to the invention is shown with a clock signal 520, which has a phase that also leads to a rectification of components of the positive half-wave of the sensor signal 510. It has been shown that the phase angle of -45° shown offers a significant improvement in robustness against deteriorated environmental conditions, in particular against water films with ground contact in the region of the sensor element. While a conventional sensor means becomes completely blind to approaches when covered by a water film with ground contact, the shown rectification and charge reversal allows approaches to be detected even under such circumstances. Curve 530 schematically shows the integrator voltage at the inverse integrator, which is part of the memory arrangement.

[0037] In this example, the duty cycle is shown as 0.5 relative to one period of the sensor signal, but a variation of the duty cycle is possible within the scope of the invention, whereby a zero crossing or inflection point is always included by the clock signal and the rectification in order to detect reactance and resistance simultaneously.

[0038] Fig. 5 shows measurements with one and the same structural measuring arrangement, but with different control. For curve 550, a conventional timing of the rectification and charge reversal was used, and in curve 560, a timing of the rectification and charge reversal according to the invention was used. In time segment 570, five approaches of an operator to the sensor element are shown, whereby the sensor element is covered with a water film, but this film is not in contact with the ground. The measuring strokes are comparable if the sensing pattern from Fig. 4a (Curve 550) and the keying pattern from Fig. 4b be applied.

[0039] In time segment 580, five approaches are shown in each case, in which the water film in the area of ​​the sensor element has ground contact. This demonstrates the more robust response of the inventive timing of the rectification and storage. While curve 550 shows no evaluable measuring strokes, the measuring strokes in curve 560, i.e., when the rectification and charge transfer are timing according to the scheme in Fig. 4b , significantly easier to detect and evaluate. This is where the simultaneous evaluation of both reactance and resistance comes into its own, and the method exhibits sufficiently high performance to enable evaluations even under these conditions.

Claims

1. Method for operating a device (10) for detecting an operating action, wherein the device comprises: - at least one sensor means (20, 20'), - a control / evaluation circuit (100) coupled to the sensor means (20, 20'), which at least temporarily outputs a periodic electrical control signal for periodically charging and discharging the sensor means, - a sensor driver circuit (170) coupled to the sensor means (20, 20') and the control / evaluation circuit (100), which outputs a sensor signal (510) tapped from the sensor means (20, 20'), - a controllable rectifier arrangement (220) coupled to the sensor driver circuit (170) for rectifying the sensor signal (510), - wherein the controllable rectifier arrangement (220) is coupled to the control / evaluation circuit (100) in order to transmit a rectified sensor signal to a memory arrangement (250) for predetermined phase sections of the sensor signal in dependence on a clock signal output by the control / evaluation circuit (100), - wherein the control / evaluation circuit (100) is coupled to the memory arrangement for determining a charge quantity accumulated in the memory arrangement (250) and for generating an evaluation signal dependent on the accumulated charge quantity, characterised in that the clock signal (520) for driving the rectifier (220) is output by the control / evaluation circuit (100) in such a way that it is synchronised with the sensor signal (510) and comprises a duty cycle according to which at least 25% and at most 75% of the period duration of the sensor signal is active, wherein during the active clock signal the rectifier (220) is controlled for rectifying and transmitting the rectified sensor signal to the memory arrangement, wherein the phase of the clock signal (520) is predetermined such that the rectification comprises at least one zero crossing of the sensor signal (510), wherein the clock signal is changed periodically or in dependence on the evaluation signal, and wherein a change in the clock signal comprises a change in the duty cycle of the clock signal.

2. Method according to claim 1, wherein a coherent rectifier is used as the rectifier (220).

3. Method according to one of the preceding claims, wherein the clock signal (520) is selected such that the phase shift of the clock signal relative to the sensor signal (510) is - 45°.

4. Method according to claim 1, wherein a change in the clock signal comprises a change in the phase of the clock signal.

5. Method according to one of the preceding claims, wherein the memory arrangement comprises an integrator.

6. Method according to one of the preceding claims, wherein an electrode arrangement is used as sensor means, which is charged and discharged in accordance with its impedance.

7. Method according to one of the preceding claims, wherein the sensor signal can be divided into a positive and a negative half-wave, wherein the duty cycle and phase of the clock signal are predetermined such that 25% of the positive half-wave and 75% of the negative half-wave are rectified.

8. Device comprising: - at least one sensor means (20, 20'), - a control / evaluation circuit (100) coupled to the sensor means, which at least temporarily outputs a periodic electrical control signal for periodically charging and discharging the sensor means (20, 20'), - a sensor driver circuit (170) coupled to the sensor means and the control / evaluation circuit (100), which outputs a sensor signal tapped from the sensor means, - a controllable rectifier arrangement (220) coupled to the sensor driver circuit (170) for rectifying the sensor signal and for transmitting the rectified sensor signal to a memory arrangement (250), - wherein the rectifier arrangement is coupled to the control / evaluation circuit (100) in order to couple the memory arrangement to the sensor driver circuit for transmission of the rectified sensor signal in dependence on a clock signal output by the control circuit for predetermined phase sections of the sensor signal, - wherein the control / evaluation circuit (100) is coupled to the memory arrangement for determining a charge quantity stored in the memory arrangement and generating an evaluation signal dependent on the charge quantity, wherein the device is configured to carry out a method according to one of claims 1 to 7.