EP2831638A1

EP2831638A1 - Capacitive positioning device

Info

Publication number: EP2831638A1
Application number: EP13704428.5A
Authority: EP
Inventors: Tobias Zibold; Andrej Albrecht
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2012-03-29
Filing date: 2013-02-14
Publication date: 2015-02-04
Also published as: DE102012205122A1; US20150084651A1; US9588162B2; CN104169742A; WO2013143763A1

Abstract

A positioning device (100) for capacitively detecting an object (110) enclosed in a medium (105) comprises a measuring electrode (140), a reference electrode (145) and a receiving electrode (150), wherein the measuring electrode with the receiving electrode forms a measuring capacitance (C1) which can be influenced by the object and the reference electrode with the receiving electrode forms a reference capacitance which cannot be influenced by the object. The positioning device further comprises an oscillator (125) for supplying the measuring capacitance and the reference capacitance with phase-shifted AC voltages and a control device for controlling amplitudes of at least one of the AC voltages, in order to adapt the effects of electrical fields of the measuring electrode or of the reference electrode on the receiving electrode to one another. To this end the electrodes are planarly formed and the measuring electrode has a larger surface area than the reference electrode.

Description

description

title

Capacitive locating device

The invention relates to a locating device. In particular, the invention relates to a device for capacitive detection of an object enclosed in a medium.

State of the art

For detecting an object hidden in a wall, such as a beam in a lightweight wall, capacitive detectors are known. Such detectors use an electrode whose charging or discharging behavior is determined to close on the dielectric object. There are also known detectors with multiple electrodes, in which a change in the capacity of a

Pair of electrodes is determined. Usually, it is necessary to manually calibrate such detectors on the wall, since the devices can not detect the wall contact itself and the capacitance of the electrodes or electrode pairs of environmental conditions, such as a temperature, humidity, an object facing away from the sensor, a ground via a user, electrical or dielectric properties of the wall material depends. In order to take account of these variable influencing factors, known devices must be calibrated on the wall, for which purpose either a corresponding control by a user or a complex sensor system is required.

DE 10 2007 058 088 A1 shows a sensor for locating dielectric objects in a medium. The sensor shown determines a relationship between a reference capacitance and a measurement capacitance, which is dependent on the position of the object with respect to electrodes of the two capacitors. DE 10 2008 005 783 B4 shows a capacitive detector as anti-trap, which compares the capacity of two capacitors with each other by means of a push-pull measuring bridge. One of the capacitances is formed by two electrodes which can be positioned relative to one another, so that a change in their relative spacing can be used to generate a signal which warns of pinching.

The invention has for its object to provide a tracking device for capacitive De detection, which requires no calibration to achieve a high accuracy.

DISCLOSURE OF THE INVENTION The invention achieves this object by means of a locating device having the features of the independent claim. Subclaims give preferred embodiments again.

There are essentially two reasons that require calibration of the locator. On the one hand, uncontrollable influences, such as an ambient temperature, an ambient humidity, a sensor-remote object or a grounding of the locating device via a user can influence the output signal. On the other hand, regardless of the object on a medium, the output signal differs from an output signal in air, wherein a material and a material thickness of the medium as well as electrical wall properties such as a dielectric constant or a conductivity can be included in the output signal.

An inventive locating device for capacitive detection of an object enclosed in a medium comprises a measuring electrode, a reference electrode and a receiving electrode, wherein the measuring electrode with the receiving electrode forms a measurable by the object measuring capacitance and the reference electrode with the receiving electrode forms a non-influenced by the object reference capacitance, further an oscillator for supplying the measuring capacitance and the reference capacitance with phase-shifted alternating voltages and a control device for controlling amplitudes of less than at least one of the alternating voltages in order to equalize the influences of electric fields of the measuring electrode or the reference electrode on the receiving electrode. The electrodes are made flat, by having only small thicknesses in relation to their surfaces. In a preferred embodiment, the surfaces are also flat. Furthermore, the

Measuring electrode on a larger surface area than the reference electrode.

By using the described electrode arrangement on a push-pull measuring bridge, interference factors which influence the capacitances between the electrodes can be compensated. Such influences may be independent of the object and the medium, such as an ambient temperature, humidity, an object facing away from the electrodes, or grounding of the locator via a user holding the device in his hand.

In a preferred embodiment, the distance of the measuring electrode to the receiving electrode is greater than the distance of the reference electrode to the receiving electrode. The push-pull measuring bridge described determines depending on a presence of the object, the change of a quotient, which is formed by a difference of the measuring capacity of the reference capacitance and a sum of these two capacitances. Influences that influence both capacities in the same way do not change the measured variable. Due to the specified geometrical appearance of the individual electrodes, the influenceability of the reference capacitance by the object can be reduced.

The measuring electrode may be at least partially and in particular in the region between the measuring electrode and the receiving electrode of a guard electrode to be concluded, which is connected to a constant potential. In this and other embodiments, it is appropriate to arrange the measuring electrode, the receiving electrode and the reference electrode in the same plane. The guard electrode may also run in this plane in this case. The constant potential can correspond in particular to the device ground. The guard electrode provides a shield in the plane, which is set to a predetermined, in particular temporally constant potential. There is no additional effort necessary to implement the shield, such a passive shielding is particularly effective when the potential at the receiving electrode due to the control condition such that AC components that are synchronous to the alternating voltages described above, disappear. The guard electrode can thus improve the quality of determination of the locating device in conjunction with the push-pull measuring bridge described.

The measuring electrode, the reference electrode and the receiving electrode can lie in one plane, wherein a screening electrode connected to a constant potential is arranged on a side facing away from the object, which covers the in-plane electrodes at least partially or, preferably, completely. An influence of an object not to be detected, in particular of a user of the locating device, can thereby be reduced. In a variant, the cover may provide only a partial cover, for example, the receiving electrode or the reference electrode may be excluded from the cover.

In another embodiment, which can be combined with the aforementioned embodiment, the carrier material has a recess between the measuring electrode and the receiving electrode.

In yet another embodiment, which can be combined with the aforementioned embodiment, the reference electrode and the receiving electrode are arranged on a surface of a planar carrier material, wherein the carrier material between the reference electrode and the receiving electrode has a recess.

Both measures are aimed at minimizing a number of electric field lines through the carrier material between the measuring electrode and the receiving electrode or between the reference electrode and the receiving electrode. An influence on the measuring capacity or on the reference capacitance by properties of the carrier material can thereby be reduced and a dependency of the capacities of temperature and humidity can be simplified. The guard electrode may be electrically connected to the shield electrode. The two different types of shielding can be connected to one another in a simple manner. This can help to easily locate the locator, thereby saving manufacturing and development costs.

Between the measuring electrode and the receiving electrode may be a plurality of conductor pieces for electrically connecting the shielding electrode to the guard electrode.

In another embodiment, which can be combined with the aforementioned embodiment, the measuring electrode and the receiving electrode are arranged on a surface of a planar carrier material, wherein the carrier material between the measuring electrode and the receiving electrode has a recess, whose boundary at least partially with a conductive layer is provided, which is electrically connected to the shield electrode and the guard electrode.

Both variants of the vertical contacting aim at the electrical connection between the guard electrode and the shielding electrode in one

Execute area between the measuring electrode and the receiving electrode such that electric field lines, in particular those are shielded by the carrier material, between the measuring electrode and the receiving electrode. A basic capacitance between the measuring electrode and the receiving electrode can thereby be reduced. As a result, the sensitivity of the measuring circuit with respect to an influence of the object can be increased. An influence on the basic capacity by properties of the carrier material can thereby be reduced and a dependence of the basic capacity on temperature and humidity can be simplified.

The measuring electrode, the reference electrode and the shielding electrode may each be coated with an insulating layer. An electrical influence, for example, of the medium on the reference or measuring capacitance can thereby be reduced. In particular, the insulating layer can serve as a moisture barrier, so that humidity does not penetrate into the substrate and the

Capacities can influence. The measuring electrode or the reference electrode may comprise a plurality of spaced-apart sections, which are connected to each other with low electrical resistance. The electrodes can thereby be arranged so that a two-dimensional determinability of the object is made possible.

The measuring electrode or the reference electrode may comprise a plurality of mutually electrically isolated sections, which are acted upon with unequal but mutually proportional signals. A sensitivity of the electrode arrangement can thus vary in different directions.

Brief Description of the Drawings The invention will now be described in more detail with reference to the accompanying figures, in which:

Figure 1 is a locating device; FIG. 2 shows an arrangement of electrodes for the locating device from FIG. 1;

FIG. 3 shows an electrical connection between electrodes on the arrangement of FIG. 2; and FIG. 4 shows an alternative electrical connection between electrodes on the

Arrangement of Figure 2 represents.

Detailed description of embodiments

FIG. 1 shows a locating device 100 for the capacitive detection of an object 1 10 enclosed in a medium 105. The locating device 100 comprises a push-pull measuring bridge 15 and an arrangement 120 of electrodes.

At the measuring bridge 15, an oscillator 125 provides two phase-shifted, preferably opposite-phase, alternating voltages of the same frequency.

The two alternating voltages are conducted to two amplifiers 130 and 135, of which at least one is controllable in its amplification factor by means of a signal. The output of the first amplifier 130 is connected to a measuring electrode 140 and the output of the second amplifier 135 is connected to a reference electrode 145.

The arrangement 120 comprises at least the electrodes 140 and 145 and a floating receiving electrode 150. The electrodes 140, 145 and 150 are arranged relative to one another such that between the measuring electrode 140 and the receiving electrode 150 a measuring capacitance C1 and between the reference electrode

145 and the receiving electrode 150 sets a reference capacitance C2. In this case, the electrodes 140, 145 and 150 are designed in such a way that the measuring capacitance C1 can be influenced by the object 110, while the reference capacitance C2 can not be influenced or to a negligible extent.

The receiving electrode 150 is connected to a measuring amplifier 155 whose output is connected to a synchronous demodulator 160. In response to a clock signal provided by the oscillator 125 whose frequency corresponds to that of the AC voltages provided to the amplifiers 130 and 135, the influences of the measuring electrode 140 and the reference electrode 145 on the receiving electrode 150 are determined alternately in time and an integrator 165, for example provided as an integrating comparator. An output of the integrator 165 is connected to an interface 170 to which a measurement signal is provided. The measurement signal is also used to control the gain factors of at least one of the amplifiers 130 and 135. If both amplifiers 130, 135 are controllable, an inverter 175 is provided in order to control the gain factors in opposite directions.

The push-pull measuring bridge 1 15 is set up to apply alternating voltages to the measuring electrode 140 and the reference electrode of the arrangement 120. suggest that the effect of a dielectric influence of the object 110 on the capacitances C1 and C2 at the receiving element 150 be the same. In this case, the reference capacitance C2 is physically constructed so that it can not be influenced by the object 110 or practically not influenced. If, for example, the object 1 10 is located asymmetrically in the region of the electrodes 140, 145, so that the capacitances C1 and C2 are influenced to a different degree by the object 110, the alternating voltages have unequally high amplitudes, so that the influences of the measuring electrode 140 and the reference electrode 145 are equal to the receiving electrode 150 in the time average. The measurement signal provided at the interface 170 reflects the modulation of the amplifiers 130, 135. If the measurement signal is higher or lower than a predetermined value that corresponds to a non-existent object 110, the object 1 10 can be deduced from the measurement signal.

FIG. 2 shows the arrangement 120 of electrodes for the locating device 100 from FIG. 1. FIG. 2A shows electrodes in a first plane facing the object 110, and FIG. 2B shows an arrangement of electrodes in a second plane, which faces away from the object 110 with respect to the first plane. In practice, the arrangement shown may be formed, for example, as a printed circuit on different layers of a board of insulating material.

In FIG. 2A, in the first plane, a first measuring electrode 205 and a second measuring electrode 210, which respectively correspond to the measuring electrode 140 in FIG. 2, a first reference electrode 215 and a second reference electrode 220, which respectively correspond to the reference electrode 145 of FIG a receiving electrode 225, which corresponds to the receiving electrode 1 15 of Figure 1 and a guard electrode 242. Interdependent electrodes 205 and 210, 215 and 220 may be electrically low impedance connected to each other. In another embodiment, electrodes 205-220 corresponding to one another are acted on with identical or unequal but mutually proportional signals, which may originate from different sources. For this purpose, for example, for each of the measuring electrodes 205 and 210, a separate amplifier 130 may be provided in the measuring bridge 15 of FIG. Each of the dual-type electrodes 205 and 210, 215 and 220 may also be implemented individually. The reference electrodes 215, 220 are smaller than the measuring electrodes 205 and 210, and preferably substantially smaller, so that the surface area of a measuring electrode 205, 210 is a multiple of the surface area of a reference electrode 215, 220. Preferably, the measuring electrodes 205 and 210 are the same size. Also preferably, the reference electrodes 215, 220 are the same size.

Preferably, the measuring electrodes 205 and 210 are farther from the receiving electrode 225 than the reference electrodes 215 and 220, and substantially further so that the distances of the measuring electrodes 205 and 210 to the

Receiving electrode 225 each amount to a multiple of the distances of the reference electrodes 215 and 220 of the receiving electrode 225.

The distance of the first measuring electrode 205 from the receiving electrode 225 preferably corresponds to the distance of the second measuring electrode from the receiving electrode 225. Also preferably, the distance of the first reference electrode 215 from the receiving electrode 225 corresponds to the distance of the second reference electrode 220 from the receiving electrode 225.

Optionally, a first counterelectrode 235 and possibly also a second counterelectrode 240 are further provided in the arrangement 120. The measuring electrodes 205, 210 and the counterelectrodes 235, 240 are preferably the same size and arranged horizontally and vertically with equal distances to each other. The measuring electrodes 205 and 210 and the counterelectrodes 235 and 240 may each be enclosed by a guard electrode 242.

Approximately in the middle of FIG. 2A, a guard electrode 232 extends in the horizontal direction, which covers the measuring electrodes 205 and 210 arranged at the top, the respectively assigned guard electrodes 242, the reference electrodes 215 and 220 and the first receiving electrode 225 from the counter-circuits arranged below. Separate electrodes 235 and 240 with their associated guard electrodes 242 and the other guard electrode 230 and reduces the capacitive coupling between the counter electrodes 235, 240 and the receiving electrode 225. The part of the arrangement 120 lying below the horizontal guard electrode 232 in FIG. 2A can also be dispensed with in other embodiments.

All Guard electrodes 230, 232, 242 are optional. The guard electrodes

242 serve to provide capacitive couplings between in the first level Electrodes 205-225, 235, 240 to interrupt. The guard electrode 230 corresponds to the receiving electrode 225 and increases the symmetry of the electrode assembly and thus the field line distribution. The guard electrodes 230, 232, 242 are connected to a predetermined, in particular temporally constant potential, for example with a device ground of the locating device 100

FIG. 1 This procedure differs from a known active shielding in that the potential of the guard electrodes is constant over time and is not tracked to any other potential The guard electrodes 242 are particularly useful when using the ones shown in FIG Push-pull measuring bridge 1 15, since the measuring bridge 1 15 is adapted to adjust the potential at the receiving electrode 150 such that AC components that are synchronous to the clock of the AC voltages at the measuring electrode 140 and the reference electrode 145, disappear.

An insulation between adjacent electrodes of the first plane can also be done with air by a recess 244 is introduced between the electrodes, as exemplified between the first reference electrode 215 and the receiving electrode 225 and between the second reference electrode 220 and the receiving electrode 225.

In the illustrated preferred embodiment, all of the electrodes 205-242 of the assembly 120 are covered by an insulating layer 246 to make resistive coupling to the ambient air medium 105 or other object more difficult. The insulating layer also serves as a moisture barrier, so that moisture, for example from the air, can not penetrate into the carrier material and influence the capacities.

FIG. 2B shows four shielding electrodes 250 which are each dimensioned and positioned such that they cover one of the measuring electrodes 205, 210 or one of the counterelectrodes 235, 240 together with the optionally associated guard electrode 242.

The shielding electrodes 250 are connected to the locating device 100 with a temporally constant potential, which may correspond to a device ground of the locating device 100. Additionally or alternatively, the shielding electrodes 250 may be connected to the guard electrodes 242. The shielding electrodes 250 can also by means of an insulating layer 246, not shown, against external

Be protected influences. FIG. 3 shows an electrical connection between different levels of the arrangement 120 of FIG. 2.

The recess 244 is inserted into a board 305, which carries the first plane of Figure 2A on its upper side and the second plane of Figure 2B on its underside. The recess 244 is inserted between the reference electrode 145 and the receiving electrode 150 in the circuit board 305. The recess 244 is optionally provided on at least one side with a conductive layer 310, the top with one of the electrodes of the first level, here exemplified by the guard electrode 242, and below with one of the electrodes of the second level, here exemplified by the shield electrode 250, electrically connected. In another example, the recess 244 may be inserted between the measuring electrode 140 and the receiving electrode 150 in the board 305. In this case, the conductive layer 210 preferably establishes an electrical contact between the guard electrode 242 on the top side and the shielding electrode 250 on the bottom side.

An alternative mechanical expression of the electrical connection is shown in FIG. Instead of the recess 244, a number of vertical holes are mounted in the board 305, through which conductor pieces 315 are performed. The conductor pieces 315 are preferably produced as plated-through holes ("vias"), for example by electroplating or by riveting.

The two variants shown in Figures 3 and 4 serve to form an air-filled region and optionally a conductor piece in a vertical direction to shield an electric field between electrodes facing each other with respect to the conductor piece in the plane. Both embodiments may be provided additionally or alternatively to a guard electrode 242 which can be used for the same purpose.

Claims

claims

Locating device (100) for the capacitive detection of an object (110) enclosed in a medium (105), comprising:

a measuring electrode (140), a reference electrode (145) and a receiving electrode (150),

- wherein the measuring electrode (140) with the receiving electrode (150) by the object (1 10) modifiable measuring capacitance (C1) and the reference electrode (145) with the receiving electrode (150) by the object (1 10) can not be influenced reference capacity ( C2) forms;

- An oscillator (125) for supplying the measuring capacitance (C1) and the reference capacitance (C2) with phase-shifted AC voltages;

- A control device (130, 135, 155, 160, 165, 175) for controlling amplitudes of at least one of the AC voltages to the influences of electric fields of the measuring electrode (140) and the reference electrode (145) on the receiving electrode (150) each other to match, characterized in that

- The electrodes (140, 145, 150) are formed flat and the measuring electrode (140) has a larger surface area than the reference electrode (145).

The locating device (100) of claim 1, wherein the distance of the measuring electrode (140) to the receiving electrode (150) is greater than the distance of the reference electrode (145) to the receiving electrode (150).

Locating device (100) according to claim 1 or 2, wherein the measuring electrode (140) is at least partially circulated by a guard electrode (242), wherein the guard electrode (242) is connected to a constant potential.

Locating device (100) according to one of the preceding claims, wherein the measuring electrode (140), the reference electrode (145) and the receiving electrode (150) lying in a plane and on a side facing away from the object (1 10) side connected to a constant potential shielding electrode (250) is ordered, which covers the in-plane electrodes (140, 145, 150) at least partially.

The locating device (100) of claims 3 and 4, wherein the guard electrode (242) is electrically connected to the shield electrode (250).

Locating device (100) according to claim 5, wherein between the measuring electrode (140) and the receiving electrode (150) a plurality of conductor pieces (315) for electrically connecting the shield electrode (250) with the guard electrode (242) are located.

Locating device (100) according to claim 5 or 6, wherein the measuring electrode (140) and the receiving electrode (150) on a surface of a planar support material (305) are arranged and the carrier material (305) between the measuring electrode (140) and the receiving electrode (150 ) has a recess (244).

The locating device of claim 7, wherein a boundary of the recess (244) is at least partially provided with a conductive layer (310) electrically connected to the shield electrode (250) and the guard electrode (242).

Locating device (100) according to one of the preceding claims, wherein the measuring electrode (140), the reference electrode (145) and the shielding electrode (250) are each covered with an insulating layer (246).

Locating device (100) according to one of the preceding claims, wherein the measuring electrode (140) or the reference electrode (145) comprises a plurality of spaced-apart sections (205, 210) which are electrically low-resistance connected to each other.

Locating device (100) according to one of the preceding claims, wherein the measuring electrode (140) or the reference electrode (145) comprises a plurality of mutually electrically isolated portions (205-220), which are applied to unequal, but mutually proportional signals.