WO2016012280A1

WO2016012280A1 - Sensor electrode for a capacitive proximity sensor

Info

Publication number: WO2016012280A1
Application number: PCT/EP2015/065879
Authority: WO
Inventors: Thomas Weingärtner; Florian Pohl; Harald Krüger
Original assignee: Brose Fahrzeugteile Gmbh & Co. Kommanditgesellschaft, Hallstadt
Priority date: 2014-07-23
Filing date: 2015-07-10
Publication date: 2016-01-28
Also published as: DE102014011037A1

Abstract

The invention relates to a capacitive proximity sensor (15) and a sensor electrode (17, 18) for the same. The sensor electrode (17, 18) comprises an elongated, flat electrode conductor (23) made of electrically conductive plastic material. For the purpose of complete or partial compensation of the length-dependent sensitivity loss of the sensor electrode (17, 18), which is caused by the specific ohmic resistance of the electrically conductive plastic material, the surface area of the conductor cross-section of the electrode conductor (23) varies in the longitudinal direction of the electrode conductor (23) and/or the electrode conductor (12) contacts a metallic feed line (26, 29) at a plurality of spaced-apart contact points (25, 28, 31, 32).

Description

description

Sensor electrode for a capacitive proximity sensor

The invention relates to a sensor electrode for a capacitive proximity sensor, in particular for use in a motor vehicle. It further relates to a capacitive proximity sensor with such a sensor electrode.

Capacitive proximity sensors are often used in automotive technology for detecting obstacles in the travel path of movable motor vehicle parts, for example as anti-pinch protection in a motorized adjusting device for a side window, a tailgate or a convertible top. Capacitive sensors are further used in automotive technology for the detection of positioning commands, which gives a vehicle user contactless by means of a hand or foot movement.

For example, from DE 10 2010 049 400 A1 a capacitive proximity sensor is known, by means of which an opening command for the automatic opening of a tailgate is detected without contact. The proximity sensor in this case comprises two elongate sensor electrodes which are mounted one above the other in the vehicle transverse direction on the rear bumper of the motor vehicle. The vehicle user issues the opening command by kicking under the rear bumper with one foot.

Conventionally, either flat conductors or round conductors are used as sensor electrodes for capacitive proximity sensors of the type described above. For example, in the case of the proximity sensor known from DE 10 2010 049 400 A1, the upper sensor electrode is designed as a flat conductor and the lower sensor electrode as a round conductor. In both cases, the actual electrode conductor of the respective sensor electrode is usually formed of metal, in particular copper. On the other hand, EP 2 159 917 A1 discloses a capacitive proximity sensor whose sensor electrodes are formed from electrically conductive plastic. Such plastic electrodes are characterized by low weight and rational manufacturability and are therefore of considerable advantage over conventional sensor electrodes with a metallic electrode conductor. In addition, plastic electrodes can be easily integrated into plastic parts made of plastics, such as bumpers, whereby the assembly costs for the associated sensor can be reduced and high reliability is achieved. In particular, a faulty mounting of the sensor electrodes and a faulty detachment of the sensor electrodes from the vehicle part can be virtually ruled out.

However, plastic electrodes, unlike corresponding metal electrodes, typically have a sensitivity that decreases markedly over the length of the sensor electrode. Comparable approaches of an object (in particular of a body part) to the sensor electrode are thus detected to different degrees by the capacitive sensor, depending on whether the object near the connection side or far from the connection side is approximated to the sensor electrode. In some applications of a capacitive sensor, this length-dependent loss of sensitivity of the sensor electrode may be desirable and - as described for example in EP 2 689 976 A1 and DE 10 201 1 1 12 274 A1 - be specifically exploited to determine the longitudinal position of the approach.

In most applications, however, the length-dependent loss of sensitivity of the sensor electrode is undesirable because it increases the risk of detection errors of the proximity sensor. In these applications, plastic electrodes can often not be used.

The invention has for its object to provide an easy and rational producible, but at the same time effective sensor electrode and an associated capacitive sensor. With regard to a sensor electrode for a capacitive proximity sensor, this object is achieved according to the invention by the features of claim 1. With regard to a capacitive proximity sensor comprising at least one such sensor electrode, the object is achieved according to the invention by the features of claim 7. Advantageous embodiments and further developments of the invention are set forth in the subclaims and the description below.

The sensor electrode has an elongated, planar electrode conductor of electrically conductive plastic material. According to a first aspect of the invention, the surface area of the conductor cross-section of the electrode conductor is varied in the longitudinal direction of the electrode conductor, so that the length-dependent loss of sensitivity of the sensor electrode caused by the specific (ohmic) resistance of the electrically conductive plastic is completely or partially compensated. According to a second aspect of the invention, for the same purpose and with the same effect, the electrode conductor is contacted at a plurality of mutually spaced contact points with a metallic lead. The two aspects of the invention can be used individually within the scope of the invention, but also in combination with one another.

The length-dependent sensitivity is characterized in this case, for example, by the signal strength of the sensor signal measured by means of the sensor electrode, which is caused by a specific object approaching a certain longitudinal position of the sensor electrode at a specific distance. Conveniently, this sensitivity is normalized by giving it in relation to the maximum signal strength that causes a comparable approach event (ie, the same object approaching the same distance) at any longitudinal position of the sensor electrode. Again, the above-mentioned object may also be a body part.

Both aspects of the invention are based on the common idea that the advantageous use of electrically conductive plastic for the electrical the conductor of the sensor electrode without the previous limitations is possible if it is possible to compensate for the disadvantages associated with this material. As is known, the disadvantages of plastic electrodes are due to the comparatively high specific resistance of the plastic material. However, the measurable ohmic resistance of the sensor electrode is correlated with the specific resistance of the plastic material on the one hand over the length of the current path formed within the electrode conductor between a considered longitudinal position of the sensor electrode and the terminal side of the sensor electrode, and on the other hand via the conductor cross section of the electrode conductor. The measurable ohmic resistance of the sensor electrode is greater, the longer the current path and the smaller the conductor cross-section. This in turn is based on the knowledge that the negative influence of the high specific resistance can be compensated on the one hand by deliberate shortening of the current paths within the electrode conductor, and on the other hand by influencing the conductor cross section. Furthermore, the sensitivity of the sensor electrode is also influenced by the size of its surface, so that the negative influence of the high specific resistance can also be varied by varying this surface.

Preferably, the electrode conductor is designed such that the surface area of its conductor cross-section increases with increasing distance to the nearest contact point. The contact point of the electrode conductor is the or each point at which the electrode conductor is contacted with a metallic lead. If the sensor electrode has only one contact point, this contact point is also always the nearest point of contact.

The surface area of the conductor cross-section is preferably increased by increasing the width of the electrode conductor with increasing distance to the nearest contact point.

In an expedient embodiment, the electrode conductor forms a continuous coherent surface. In an alternative embodiment of the invention, however, the electrode conductor can also be designed such that it holes or Has incisions. In particular, the electrode conductor can be formed in the context of the invention by a net-like conductor structure. In these cases, the surface area of the conductor cross-section is optionally increased by the fact that the holes or incisions are formed or arranged with increasing distance to the nearest contact point with decreasing size and / or density.

In order to shorten the current paths within the electrode conductor, the latter has, in an expedient embodiment, a contact point at both longitudinal ends. The electrode conductor is therefore contacted at both longitudinal ends. The two contact points are expediently contacted by means of two separate metallic leads. The separate supply lines can thereby be used not only for signal transmission to the sensor electrode, but also - in the context of a diagnostic function - for testing the electrical continuity of the current paths formed over the leads and the entire length of the sensor electrode. As a result, wire breaks or other contact errors can be detected.

Additionally or alternatively, the electrode conductor is guided in parallel in an advantageous embodiment of the invention, a metallic lead over at least part of its length. In this case, this feed line is contacted with the electrode conductor at at least two spaced-apart contact points.

The proximity sensor according to the invention comprises an electronic control and evaluation unit and at least one associated sensor electrode of the type described above. The control and evaluation unit is formed in particular by a microcontroller with a control and evaluation program (firmware) implemented therein. Alternatively, however, it can also be formed by a non-programmable hardware circuit, in particular an ASIC.

Embodiments of the invention will be explained in more detail with reference to a drawing. Show: 1 is a rough schematic side view of a rear part of a motor vehicle, which is provided with a two elongated sensor electrodes having capacitive proximity sensor for contactless opening of a tailgate, and

1 shows a schematic representation of the proximity sensor according to FIG. 1 with one of the two sensor electrodes, an object guided along the sensor electrode along a specific distance to determine the length-dependent loss of sensitivity, and in a schematic diagram the profile of the length-dependent sensitivity against a longitudinal position along the sensor electrode .

FIGS. 3-5 show the proximity sensor with different further embodiments of the sensor electrode and the respective associated course of the length-dependent sensitivity.

Corresponding parts and sizes are always provided with the same reference numerals in all figures.

Fig. 1 shows a rear 1 of a motor vehicle 2, which is provided with a movable vehicle door in the form of a tailgate 3. The tailgate 3 is pivotally articulated about an upper edge 4 of the stern 1. By pivoting the tailgate 3, the same along a (indicated in Fig. 1 by an arrow) Verstellwegs P reversibly between an open position 5 and a closed position 6 are moved. In the open position 5 and the closed position 6, the tailgate 3 is shown in each case with dashed lines. With solid lines, the rear flap 3 is shown in an (arbitrarily selected) intermediate position 7 between the open position 5 and the closed position 6.

For automatic adjustment of the tailgate 3, the motor vehicle 2 is equipped with an adjusting device 10. The adjusting device 10 comprises an electric servo motor 1 1 and a (in Fig. 1 only indicated) actuating mechanism 12, via which the servomotor 1 1 mechanically with the tailgate 3 for their adjustment is coupled. For controlling the servomotor 1 1, the adjusting device 10 also comprises an electronic engine control unit 13.

For non-contact detection of opening commands of a motor vehicle user for the tailgate 3, the motor vehicle 2 is further equipped with a capacitive proximity sensor 15. The proximity sensor 15 comprises an electronic control and evaluation unit 16 and two sensor electrodes 17 and 18.

The two sensor electrodes 17 and 18 are arranged parallel and substantially one above the other on the (not visible from the outside) rear of a rear bumper 19 of the motor vehicle 2 and extend here horizontally in the vehicle transverse direction over a large part of the vehicle width.

During operation of the proximity sensor 15, an electrical alternating voltage is applied to the sensor electrodes 17 and 18 by the control and evaluation unit 16, under the effect of which each of the two sensor electrodes 17, 18 in a space respectively upstream of the sensor electrodes 17, 18 (hereinafter referred to as detection space 20 or 21) generates an electric field. As can be seen from FIG. 1, the sensor electrodes 17 and 18 are designed and aligned such that the detection space 20 of the upper sensor electrode 17 extends substantially horizontally from the bumper 19, while the detection space 21 of the lower sensor electrode 18 extends the bumper 19 flanked substantially at the bottom.

When a body part, in particular a foot of a vehicle user approaches the bumper 19 and is thereby introduced into the detection spaces 20 and 21, this body part influences the sensor electrodes 17 due to the electrical conductivity of the human body tissue and the capacitive coupling of the body tissue to the ground , 18 outgoing electric field and thus the measurable at the sensor electrodes 17,18 capacity. As a measure (hereinafter "sensor signal") for the capacity, the control and evaluation unit measures unit 16, for example, the current strength of the current flowing at a predetermined voltage to the sensor electrode displacement current.

In order to signal a door opening request, the vehicle user conventionally performs a kick-like foot movement under the bumper 19. The temporal capacity change caused thereby is detected by the control and evaluation unit 16. If the course of the detected sensor signal and thus the measurable capacitance change correspond to stored triggering criteria, the control and evaluation unit 16 interprets the capacitance change as the opening command and outputs a corresponding opening signal O to the engine control unit 13, which then opens the tailgate by activating the servomotor 1 1 3 causes.

FIG. 2 shows, roughly schematically, the proximity sensor 15 with the control and evaluation unit 16 as well as by way of example with one of the two sensor electrodes 17, 18.

As can be seen from this illustration, the sensor electrode 17,18 comprises a planar, along a longitudinal direction elongated electrode conductor 23. The electrode conductor 23 is made of electrically conductive plastic, such as polyaniline (PAni) and in the embodiment of FIG elongated rectangular strip with constant width.

At one longitudinal end 24, the sensor electrode 17,18 has a contact point 25 made of metal (in particular copper), via which a feed line 26 is electrically connected to the electrode conductor 23. Furthermore, in the embodiment according to FIG. 2, the sensor electrode 17, 18 has a further contact point 28 at the opposite longitudinal end 27, via which a further feed line 29, which is separate from the feed line 26, is electrically contacted with the electrode conductor 23.

The electrode conductor 23 is preferably insulated from the environment by means of a layer of electrically insulating plastic in order to avoid a short circuit of the electrode conductor 23 with surrounding vehicle parts and to protect the electrode conductor 23 from damaging environmental influences (water, dirt, etc.) protect. In an expedient embodiment, the sensor electrodes 17, 18, and in particular their respective electrode conductors 23, are integrated in the bumpers 19, which are likewise made of plastic.

About the leads 26 and 29, which are formed as ordinary insulated wire or stranded copper conductors, the sensor electrode 17,18 (more precisely whose electrode conductor 23) is electrically connected to the control and evaluation unit 16.

Due to the comparatively high specific resistance of the plastic material used for the electrode conductor 23, the sensor electrode 17, 18 has a sensitivity which varies over its length. Characteristic of the sensitivity is the signal strength of the control signal, which causes the approach of a certain object 30 to a certain distance A to a certain longitudinal position x of the sensor electrode 17,18. In contrast to the diagram of FIG. 2, the distance A is measured perpendicular to the surface of the electrode conductor 23.

In the following, "(length-dependent, normalized) sensitivity" S denotes a measured variable for the determination of which the signal strength of the sensor signal, which is caused by the object 30 approximating the given longitudinal position x of the sensor electrode 17, 18 at the specific distance A, is applied to the maximum signal strength is normalized (ie divided by the maximum signal strength) which causes the same object 30 to approach the same distance A at any longitudinal position x of the sensor electrode 17, 18. As indicated in Figure 2, the object 30 is particularly galvanic or at least This object 30 may in particular be a body part of the human body, in particular a foot or a hand.

To determine the course of the sensitivity, for example-as is indicated schematically in FIG. 2 -the object 30 can be displaced parallel to the longitudinal direction of the sensor electrode 17, 18, while maintaining the distance A; when continuously the sensor signal of the proximity sensor 15 is detected. The course of the sensitivity S shown in the diagram of FIG. 2 results here from the fact that the maximum of the detected curve of the sensor signal is set to the value one by the normalization described above. The standardization has the advantage that the values of the sensitivity S are largely independent of the object 30 used for their determination and the distance A at which this object 30 approaches the sensor electrode 17, 18. The normalized sensitivity S can theoretically assume values between one and zero or be given as a percentage between 100% and 0%.

A conventional plastic electrode with a strip-shaped planar electrode conductor of constant width, which is contacted only one longitudinal end with a metallic lead, has a length-dependent, normalized sensitivity S ', which has its maximum (and thus the value of one) at the contact point assigned to this longitudinal end and decreases with increasing distance to this contact point. The typical course of this sensitivity S 'of conventional sensor electrodes is plotted in the diagram according to FIG. 2 for the purpose of comparison with a dashed line.

As can be seen from FIG. 2, the effect achieved by the second contact point 28 at the second longitudinal end 27 of the electrode conductor 23 is that the sensitivity S there is likewise raised at least approximately to the value 1. Although the sensitivity also decreases in the case of the sensor electrode 17, 18 according to FIG. 2 between the two contact points 25 and 28. However, the loss of sensitivity is considerably less pronounced here than in the case of a conventional sensor electrode contacted only on one side. The sensitivity loss caused by the comparatively high specific resistance of the electrode material is thus partially compensated.

In the embodiment according to FIG. 3, the sensor electrode 17, 18 comprises, in addition to the contact points 25 and 28, further contact points 31 and 32. The contact points 25, 28, 31 and 32 are distributed here over the length of the electrode conductor 23 at regular intervals. In the embodiment of FIG. 3, the second Supply line 29 not available. Instead, the supply line 26 is guided over the entire length of the sensor electrode 17,18 parallel to the electrode conductor 23 and contacted with all contact points 25,28,31 and 32. Unlike in the illustration according to FIG. 3, the supply line 26 is preferably mechanically connected to the electrode conductor 23 over the entire length of the sensor electrode 17, 18.

As can be seen from the diagram of FIG. 3, the increase in the number of contact points 25, 28, 31 and 32 (compared to FIG. 2) makes the course of the sensitivity S even more consistent with a constant progression with the value S = 1 as in the embodiment of FIG. 2. The caused by the high resistivity of the conductor material of the electrode conductor 23 sensitivity loss is thus compensated even more.

4, the electrode conductor 23, similar to a conventional sensor electrode, only at the longitudinal end 24 in the (here single) contact point 25 with the (here single) lead 26 contacted. In order to compensate for the loss of sensitivity to be expected in this configuration of the sensor electrode 17, 18, according to FIG. 4, the electrode conductor 23 is designed in such a way that its width continuously increases with increasing distance from the longitudinal end 24. As a result of this trapezoidal shaping of the electrode conductor 23, it is achieved that the conductor cross section and the surface of the electrode conductor 23 relevant to the field generation also increase with increasing distance from the longitudinal end 24. As can be seen from the diagram of FIG. 4, this measure achieves an at least approximately constant course of the sensitivity S over the entire length of the sensor electrode 17, 18.

In the embodiments according to FIGS. 2 to 4, the electrode conductor 23 respectively forms a completely filled, continuous contiguous surface. Deviating from this, the electrode conductor 23 is provided with holes 33 in the embodiment according to FIG. 5. The remaining electrode conductor 23, which again has a constant width over its entire length in the illustrated example, thus forms a grid-like conductor structure. In order to achieve the same effect in the thus designed electrode conductor 23 as in the embodiment of FIG. 4, namely an increasing with increasing distance to the (again single) contact point 25 surface area of the conductor cross-section and an increasing effective surface, the holes 33 are designed in that their size decreases - as the density of the holes 33 remains constant - with increasing distance to the contact point 25. Alternatively or additionally, the density of the holes 33 can be lowered with increasing distance to the contact point 25. As can be seen from the diagram for FIG. 5, a substantially constant course of the sensitivity S over the entire length of the sensor electrode 17, 18 is also achieved by this measure.

The sensor electrodes 17 and 18 of the proximity sensor 15 may be the same, in particular after each of the embodiments shown in FIGS. 2 to 5, constructed. Alternatively, the sensor electrodes 17 and 18 may also be constructed differently. In particular, one of the two sensor electrodes 17 or 18 may also be designed in a conventional manner.

The invention will be particularly apparent in the embodiments described above, but is not limited thereto. Rather, numerous other embodiments of the invention may be inferred from the claims and the foregoing description. In particular, the measures for compensating the loss of sensitivity caused by the specific resistance of the electrode material can be combined as desired with reference to FIGS. 2 to 5.

Rear

motor vehicle

tailgate

top edge

open position

closed position

intermediate position

locking device

servomotor

actuating mechanism

Engine control unit

Proximity sensor

Control and evaluation unit Sensor electrode

sensor electrode

bumper

detection space

electrode conductor

longitudinal edge

contact point

supply

longitudinal end

contact point

supply

object

contact point

hole

Move away O Opening signal A Distance x longitudinal position S Sensitivity S 'Sensitivity

Claims

claims

1 . Sensor electrode (17,18) for a capacitive proximity sensor (15) having an elongated, planar electrode conductor (23) made of electrically conductive plastic material, wherein for complete or partial compensation of the caused by the specific ohmic resistance of the electrically conductive plastic material, length-dependent loss of sensitivity of the sensor electrode (17,18)

the surface area of the conductor cross-section of the electrode conductor (23) in

Is varied longitudinally of the electrode conductor (23) and / or

- The electrode conductor (12) at a plurality of spaced contact points (25,28,31, 32) with a metallic lead (26,29) is contacted.

2. Sensor electrode (17,18) according to claim 1,

wherein the area of the conductor cross-section of the electrode conductor (23) increases with increasing distance to the nearest contact point (25,28,31, 32).

3. Sensor electrode (17,18) according to claim 2,

wherein the width of the electrode conductor (23) increases with increasing distance to the nearest contact point (25,28,31, 32).

4. Sensor electrode (17,18) according to claim 2 or 3,

wherein the electrode conductor (23) has holes (33) or cuts, and wherein the size and / or density of the holes (33) or cuts with decreasing distance to the nearest contact point (25,28,31, 32) decreases.

5. sensor electrode (17,18) according to one of claims 1 to 4,

wherein the electrode conductor (23) at both longitudinal ends (24,27) each having a contact point (25,28), and in these contact points (25,28) by means of two separate metallic leads (26,29) is contacted.

6. sensor electrode (17,18) according to one of claims 1 to 5,

wherein the metallic conductor (23) is parallel led over at least part of its length to a metallic lead (26), and wherein said lead (26) contacts the electrode lead (23) at at least two spaced contact points (25, 28, 31, 32) is.

7. Capacitive proximity sensor (15) with an electronic control and

Evaluation unit (16) and at least one associated sensor electrode (17,18) according to one of claims 1 to 6.