EP3500826A1

EP3500826A1 - Evaluation circuit for a capacitive sensor, capacitive sensor, and actuator in a motor vehicle

Info

Publication number: EP3500826A1
Application number: EP16766277.4A
Authority: EP
Inventors: Jörg Schulz
Original assignee: IFM Electronic GmbH
Current assignee: IFM Electronic GmbH
Priority date: 2016-08-19
Filing date: 2016-09-14
Publication date: 2019-06-26
Also published as: US10684142B2; WO2018033223A1; DE102016215570A1; US20180274950A1

Abstract

The invention relates to an evaluation circuit for a capacitive sensor for detecting the distance, the speed, or the position of an object, comprising a reference capacitance (1) and a measuring capacitance (2), wherein a square wave voltage (3) is applied to the reference capacitance (1) and the measuring capacitance (2) via a resistor, and a pulse (7) which has a variable duration is obtained with the aid of a logic linking unit (4) and which duration represents a measure of the respective measuring capacitance (2). According to the invention, the reference capacitance (1) is connected to the input of a first switching stage (41, 43) and the measuring capacitance (2) is connected to the input of a further switching stage (43, 41). A single measuring capacitance (21) has a capacitive coupling (15) to an auxiliary electrode (8), and the switching stages (41, 43) are part of a logic linking unit (4) which is designed such that reaching the threshold voltage of a first switching stage (41, 43) determines the activation time of an output signal (7) and reaching the threshold voltage of a further switching stage (43, 41) determines the deactivation time of the output signal (7), the output of the logic linking unit (4) being connected to the input of an integration stage, and a charging capacitor (Ca) being charged or discharged via the output of the integration stage (5). The invention also relates to a capacitive sensor and an actuator comprising said capacitive sensor.

Description

Evaluation circuit for a capacitive sensor, capacitive sensor and actuator in a motor vehicle

The invention relates to an evaluation circuit for a capacitive sensor according to the preamble of patent claim 1.

Capacitive sensors are widely used not only in automation technology, but recently also in automotive technology, where they u. a. be used as trunk, door opener, or seat occupancy recognition application.

AT 403 213 B discloses a capacitive humidity sensor with a square-wave generator whose signal is supplied to an AND gate via two different signal paths, one signal path being straight and the other having a measuring electrode whose capacitance influences the signal shape and thereby reaching a switching threshold delayed.

WO 2007 025 785 A1 discloses a capacitive sensor with a square-wave generator whose signal is supplied via two different signal paths to an XOR gate, wherein one signal path contains a measuring electrode and the other a reference electrode.

DE 10 2012 106 526 AI discloses a capacitive door handle sensor for a motor vehicle with at least two electrodes with different monitoring areas, wherein one electrode acts as a reference electrode.

DE 10 2012 224 007 AI discloses an arrangement and a method for determining the capacitance of a measuring capacitor in a detectable with an analog-to-digital converter voltage with a charge transfer device for transferring the charge of an unknown capacitance C _X on a measuring capacitor C _L , however, only the Comparison of a single unknown capacity C _{X is provided} with a reference capacity C _re f.

DE 10 2014 216 998 A1 shows an evaluation circuit for a capacitive sensor with a plurality of measuring capacitances and a reference capacitance, wherein the measuring capacitances are successively compared in a predetermined time regime with the same reference capacitance.

The object of the invention is to provide a comparison with the circuit shown in DE 10 2014 216 998 AI again cost-optimized circuit, which also has additional opportunities to detect the capacitive environmental effects. The object of the invention is achieved with the characterizing features of claim 1. The subclaims relate to the advantageous embodiment of the invention.

The essential idea of the invention is to compare the measuring capacity in a predetermined time regime with a reference capacitance and to influence the respective capacitance measurement controllable by an additional auxiliary electrode. This is the

Reference capacitance with the input of a first switching stage and the measuring capacitance connected to the input of a further switching stage, these switching stages are formed, for example, as a NAND gate and together form a logical combination unit which is designed so that the switching time of the first switching stage determines the turn-on of an output signal and the switching time of a further switching stage determines the switch-off time of the output signal or that the switching time of the first switching stage determines the switch-off time of an output signal and the switching time of a further switching stage determines the switch-on time of the output signal. The output signals of the logic operation unit are the input of a

Supplied to the integration stage. Via the output of the integration stage, which can also act as a current source, a charging capacitor is charged. The length of time of the o. G.

logic operation unit generated output pulses determines the voltage of the charging capacitor.

In an advantageous embodiment, the reference capacitance or the measuring capacitance is connected to a time influencing unit, which has a capacitor and a voltage source, or is connected to a controllable voltage source.

The time influencing unit is used for targeted influencing by the

Reference capacitance or the measuring capacity generated delay time.

The advantage of the invention is that a targeted capacitive influencing of the measuring electrode is possible by an auxiliary electrode which is subjected to a voltage signal substantially simultaneously with a measuring electrode, so that in this way further spatial regions in the vicinity of the measuring electrode can be evaluated capacitively without requiring a separate measuring channel with additional circuit complexity for measuring the capacitance of an electrode.

Thus, for example, with only one IC of the type 74HC132, a capacitive sensor with several spatially distinguishable areas can be constructed, which on the one hand leads to a saving of components and on the other hand offers additional possibilities for detecting capacitive environmental influences.

The invention will be explained in more detail with reference to the drawings.

1 shows an evaluation circuit according to the invention with a passive auxiliary electrode.

2 shows an evaluation circuit according to the invention with an active auxiliary electrode.

FIG. 3 shows a microcontroller belonging to the circuits in FIGS. 1 and 2

Shift stage.

Fig. 4 shows the timing diagram for controlling the measurement in detail.

Fig. 5 shows the embodiment of the circuit according to the invention in a vehicle door handle.

Fig. 6 describes an example with two sensor electrodes and an auxiliary active electrode.

Fig. 7 describes an example with a sensor electrode and two auxiliary electrodes.

Fig. 1 shows an embodiment with an integrated circuit of the type 74HC132 with four switching stages (NAND gate) 41, 42, 43, 44, which form a logic operation unit 4, wherein in the idle state, the controllable gate input designated 41

Switching stage is at the logic state "high", so that their output, and thus the control signal 6 assumes the logic state "low".

This has the consequence that for the duration of this state, the switching stages 42, 43 are also on their non-externally controllable input also on 'Tie' and thus are technically blocked, so that their outputs are "high" for the duration of this signal state, the switching stage 44 assumes the state "low at its output and the integration stage 5 is likewise blocked, the charge capacitor denoted Ca here being charged, which was previously charged by the switch S, which in turn is controlled by the microcontroller μC shown in FIG becomes.

The control input of the switching stage 41, which is not connected to the operating voltage, is connected to a time influencing unit 9 which, in addition to R _re f and C _re f, has two capacitors C _rl and Cr2 to which the auxiliary voltage sources Ui and U _{2 are} connected.

In the idle state, the clock input Clock Ref and one of the clock inputs Clock l, Clock_2, is set to "High." In this example, assume that the clock input Clock l is currently at "High". The other clock input is at "low. In this example, the switching stage 42 whose clock input is high is for pulse generation while the other clock input, in this example the switching stage 43, remains inhibited by the logical input signal "Low.

To generate a pulse at one of the outputs of the switching stages 42, 43, and thus also at 44, by an externally connected, shown in Fig. 3 control unit J5, for example, a microcontroller (μθ), both the clock input "Clock Ref and the In this way, the signal applied to "Clock Re" reaches the input of the switching stage 41 via the low-pass filter R _re f, C _re f and triggers on reaching the "clock" input Threshold voltage at the output of a positive voltage jump, the delay time of this

Voltage jump is influenced by the time influencing unit (9), with the aid of which the signal to C _re f can be shifted in time. For this purpose, the

Auxiliary voltages Ui and U ₂ applied. These voltages and also the three clock signals shown in FIG. 4 (Clock Ref, Clock l, Clock_2) can be generated by the previously described control unit (μϋ).

For a meaningful pulse generation, all time constants and all control signals, which are located in front of the gate terminals of the gates 41 and 42, 43, are dimensioned or adjusted such that the voltage at the gate input of the gate 41 first reaches the negative switching threshold. This causes the non-accessible gate inputs 42, 43 of the logic state of "low" to "high" changes, so that, as shown, the gate 42, at its externally accessible input of the logic state "high" is applied , its output to "low switches and thus the subsequently connected logic element (NAND gate) 44, the subsequently connected integration stage 5 controls. This initiates a discharging process of the capacitor designated Ca via the integration stage 5. The switch-on time of this

Output signal is thus determined by the switching time of the first switching stage 41. The other gate 43, where the externally accessible input from the outset on "low, remains thus signal technology blocked.

Thereafter, the voltage at the externally accessible gate input whose connected clock input simultaneously with the signal "Clock Ref from" high "to" low reaches its negative switching threshold, so that the just switched from "high" to "low" gate output of the switching stage 42 switches back to "high" back, the gate 44 switches back to "low back and thus the control of the subsequently connected integration stage 5 again interrupts, causing the discharge of the with Ca designated capacitor is terminated. Thus, the switch-off of this output signal from the switching time of the further switching stage 42 is determined.

Thus, upon reaching the threshold voltage of a first switching stage 41, a start signal and upon reaching the threshold voltage of another switching stage 42 or 43, a stop signal is generated.

The time influencing unit 9 includes for selectively influencing the by the

Reference capacitance 1 (C _re f) generated delay time a capacitor C _rl and one of the evaluation ^ C) controllable voltage source Ui.

Thus, the time duration with which the integration stage 5 is driven depends on the electrode capacitance to be measured, which is assigned to the respectively activated clock input (Clock 1, Clock_ 2). For evaluating any capacitance to be measured, the respective assigned clock input is activated in the manner described above.

The auxiliary electrode 8 with the designation EL H lies on a further terminal IN I of the control unit .mu.C of FIG. 3, is supplied by a resistor (Re3) from one of the clock inputs Clock l, Clock_2, and is capacitive with one of the measuring electrodes 21, 22 (EL I, EL 2) coupled. In the example shown, the auxiliary electrode 8 is fed by the clock input Clock_2 and is capacitively coupled to the measuring electrode 22 (EL_2).

The IN IN terminal can be operated in 2 different modes during pulse generation of Clock_2, for example high impedance and low impedance. As a result, in the high-impedance mode, the clock signal applied to Clock_2 is likewise conducted to the auxiliary electrode 8 (EL H), while in the low-impedance mode, the clock signal applied to Clock_2

Clock signal is short-circuited by IN I and thus does not appear on the auxiliary electrode 8 (EL H). Thus, in the two different modes, the capacitance measurement at 22 (EL 2) is influenced differently via the capacitive coupling between the electrodes 8 (EL H) and 22 (EL 2), which in the signal evaluation provides information about the mutual capacitance between the electrodes 8 (EL H) and 22 (EL 2) allowed.

This can be useful, for example, in order to be able to detect the influence of objects located outside the sensor arrangement, for example water, conductive primer or a chromium coating on the housing of the device, and thus to be able to optimize the detection characteristic of the sensor, for example by means of adapted parameterization. On this way can also suppress unwanted operating conditions or the influence of variable

Mounting environments are detected.

Fig. 2 shows a circuit arrangement as in Fig. 1, which differs only by the control of the auxiliary electrode 8 (EL H). In this embodiment, the

Auxiliary electrode 8 (EL H) powered by an additional clock input Clock_3. The embodiment of Fig. 2 offers the additional possibility of the control signal

Clock_3 temporally both the measurement at 21 v (EL_l) and the measurement at 22 (EL_2) to assign and thus both mutual capacities to evaluate. If Clock_3 is generated simultaneously with Clock 1, then the capacitance between the electrodes 8 (EL H) and 21 (EL I) is affected. If, on the other hand, Clock_3 is generated simultaneously with Clock_2, then the capacitance between the electrodes 8 (EL H) and 22 (EL 2) is influenced.

In addition, the control signal for Clock_3 can be generated both in-phase and out-of-phase, which allows the double Nutzsignalhub. This embodiment requires a further connection of the MikrocontroUers which allows this mode. Depending on the type of MikrocontroUers μC (J5 of Fig. 3), the variant of FIG. 1 or the variant of FIG. 2 may be preferred.

FIG. 3 shows a microcontroller for controlling and evaluating the circuits indicated in the two preceding figures. For Fig. 1, the port PI (Clock_3) is not needed, and can be left free. The same applies to Fig. 2 and the terminal P13 (IN I). The terminal P8 (A) is connected to a switching stage (T2), which can transmit, for example, a switching signal or a bus signal, so as to transmit the desired measurement results or Auswertekriterien using the switching stage T2 to an external control unit.

FIG. 4 shows an example, associated pulse diagram in detail. The signals corresponding to the clocks of Fig. 1. It can be seen for the gate 41 specific clock signal (Clock Ref), the gate 42 for certain clock signal (Clock l), the specific gate 43 for the clock signal (Clock_2) and at the Auxiliary electrode 8 (EL H) adjacent

Signal voltage. This signal voltage is in the illustrated signal pattern in

Evaluated interaction with the clock signal (Clock_2), which drives the electrode 22 (EL 2). Shown are two different modes, wherein in one mode, the clock signal Clock Ref is generated simultaneously with the clock signal Clock_2. In the diagram this is the time 52μ8. In the other mode, which generates another clock signal at the time 84μβ, an additional signal edge at EL H is visible, whereby a

Influencing the mutual capacity between EL 2 and EL H is achieved. With "Tl" designated time used to produce a defined initial state and must be at least as large as the sum of all delay times that may affect the electrical potential of the relevant capacity, and thus ensures a reproducible flow of measurement.

5 shows a constructive embodiment in the door handle of a motor vehicle, wherein the operation of the auxiliary electrode 8 and the influence of the mutual capacitive coupling (electric field 15) between the auxiliary electrode 8 and electrode 22 is shown, which is influenced by an approximated influencing object 16. The constructive sensor arrangement here includes the electronics 11 inclusive

Electrode system 8, 13, 22, housing 10 and other design-related elements, which also affect the mutual capacitive coupling between the auxiliary electrode and another electrode. Sensory usable, so in the sense of a detection of certain operating cases or influencing factors such. Water or unwanted

Operating cases, however, the arrangement is only if at least part of the capacitive coupling 15 extends outside of this constructive sensor arrangement, so that it can be influenced by external objects 16.

FIG. 6 describes a particularly simple battery-operated exemplary embodiment in which the logical combination unit 4 consists of only two NAND gates 41, 43. At the input of the first switching stage 43, the electrodes 21, 22 are connected. The function of the further switching stage, at whose input the reference capacitance 1 lies, is taken over here by the gate 41. The circuit includes two sensor electrodes 21, 22 and an auxiliary electrode 8, which is actively acted upon by an auxiliary signal (Clock_3).

In this arrangement, therefore, the switch-on time of the output signal 7 of the logical combination unit 4 is determined by the switching points of the switching stage 43 to which the measuring capacitance is connected. The switch-off time of the output signal 7 of the logical combination unit 4 is determined by the switching point of the switching stage 41 to which the reference capacitance is connected. The charging capacitor Ca at the output of the

Integration device 5 is loaded in this embodiment.

Fig. 7 shows a power-saving embodiment for battery-powered applications, wherein the logic operation unit 4 consists of only two NAND gates 41, 43, and a NAND gate further simplified and optionally can also be implemented as an inverter. Here is only a single measuring capacity 2 available. Nevertheless, several positions can be spatially evaluated, depending on which of the two auxiliary electrodes 8 active with an auxiliary signal (Clock Hl, Clock_H2) is applied. In addition, even several auxiliary electrodes can be actively acted upon simultaneously with an auxiliary signal (Clock HI, Clock_H2) in order to gain additional information through the functional modes thus generated, for example for more precise differentiation of specific operating conditions or factors such as water or contamination. At the input of the first switching stage 43, the electrode 21 is connected. The function of the further switching stage, at whose input the reference capacitance 1 lies, is taken over here by the gate 41. The circuit includes a sensor electrode 21 and two auxiliary electrodes (8, EL H1, EL H2) which are actively acted upon by an auxiliary signal (Clock Hl, Clock_H2).

In this arrangement, the switch-on time of the output signal 7 of the logical combination unit 4 is determined by the switching point of the switching stage 43, to which the measuring capacitance is connected. The switch-off time of the output signal 7 of the logical combination unit 4 is determined by the switching point of the switching stage 41 to which the reference capacitance is connected. The charging capacitor Ca at the output of the integration device 5 is charged in this embodiment.

reference numeral

1 reference capacity, C _re f

2 measuring capacity (s) Cel, Ce2, Ce3, measuring electrode (s) => 21 and 22

3 square-wave voltage, clock signal

4 Logical logic unit with the switching stages, (41, 42, 43, 44) => NAND gate 74HC132 with Schmitt trigger

5 integration stage (bipolar Miller integrator or current source) with transistor Tl and output capacitor Approx.

6 control signal for the non-accessible from the outside inputs of the gates 42 and 43rd

7 output signal of the logic operation unit

8 auxiliary capacitance, auxiliary electrode

9 Time control unit connected to the reference or measuring capacity

10 outside door handle housing

11 Capacitive sensor electronics

12 supply and data line

13 electrode lead

14 vehicle body

15 Electric field, capacitive coupling

16 object, influencing object

17 External control unit

18 power supply, battery

19 Electric vehicle mass

20 earth potential

21 First measuring electrode

22 Second measuring electrode

Claims

claims

1. evaluation circuit for a capacitive sensor for detecting the distance, the speed or the position of an object, with a reference capacitance (1) and a measuring capacitance (2), wherein the reference capacitance (1) and the measuring capacitance (2), via a resistor with a square-wave voltage (3) is applied, and with the aid of a logical combining unit (4) a time-variable pulse (7) is obtained whose duration represents a measure of the measuring capacitance (2),

characterized in that the reference capacitance (1) is connected to the input of a first switching stage (41, 43) and the measuring capacitance (2) to the input of a further switching stage (43, 41), wherein a single measuring electrode (21) with at least one Auxiliary electrode (8) has a capacitive coupling (15), wherein the switching stages (41, 43) are part of a logical combination unit (4), which is designed such that reaching the threshold voltage of a first switching stage (41, 43) the switch-on of a Output signal (7), and reaching the

Threshold voltage of a further switching stage (43, 41) determines the switch-off time of the output signal (7), and the output of the logical combination unit (4) is connected to the input of an integration stage (5), wherein via the output of the integration stage (5) a charge capacitor ( Ca) is charged or discharged.

Second evaluation circuit for a capacitive sensor according to claim 1, characterized

in that the capacitive coupling (15) between an auxiliary electrode (8) and a measuring electrode (21) can be influenced by objects (16) which are located constructively outside the sensor arrangement, wherein a plurality of positions are spatially evaluated with a single measuring electrode (21) can.

3. evaluation circuit for a capacitive sensor according to claim 1 or 2, characterized in that the reference capacitance (1) with a time influencing unit (9) is connected, wherein the time influencing unit (9) comprises a capacitor (C _rl , C _r2 ) and a controllable voltage source (Ul, U2), and targeted

Influencing the delay time generated by the reference capacitance (1) is used.

4. evaluation circuit for a capacitive sensor according to claim 1 or 2, characterized in that the measuring capacitance (2) with a time influencing unit (9) is connected, wherein the time influencing unit (9) comprises a capacitor and a has controllable voltage source, and is used to selectively influence the delay time generated by the measuring capacitance (2).

5. Capacitive sensor with an evaluation circuit according to claim 1, 2 or 3.

6. actuator in a motor vehicle with a capacitive sensor according to claim 4.