EP1828524B1 - Sensor using the capacitive measuring principle - Google Patents

Description

The invention relates to a sensor with capacitive measuring principle and a method for detecting an approaching dielectric medium, preferably for detecting a human body part for use in a anti-trap, with a capacitor and an evaluation, wherein the caused by the medium change in the capacitance of the capacitor can be measured is.

Capacitive proximity sensors have long been known in practice. They consist of specially designed capacitors whose stray electric field is affected by approaching objects. Non-conductive objects lead to an increase in the capacitance of the sensor due to their relative to the ambient air increased dielectric constant. The capacitance change depends on the distance of the object from the sensor, its position relative to the sensor, its dimension and its dielectric constant. To detect an approaching object, the capacitance of the sensor must be determined, for which purpose all capacitance measuring methods known to the person skilled in the art can be used. In most cases, the sensor is part of a resonant circuit which is detuned by objects approaching or, given suitable dimensioning of the resonant circuit, becomes capable of oscillation only when an object is present in the stray field of the sensor. Specially designed proximity sensors can be used in a particularly advantageous manner in a trapping protection. Examples show the DE 102 48 761 A1 and the EP 1 154 110 B1 ,

Due to the high water content of the human body and the very high dielectric constant of water, a human body part in the stray field of a proximity sensor leads to a particularly high measuring effect. However, this not only detects the presence of a human body part, but also water and / or moisture that is in the field of the sensor. This leads to incorrect measurements, especially in rain or fog.

In the mentioned DE 102 48 761 A1 This problem is solved in that the measurement results of several such sensors are compared with each other and assuming a uniform water / moisture distribution in the area of the combined sensors and the associated increase in the same capacity of all sensors, the threshold value of the individual sensors is adjusted. However, the correctness of this assumption can not always be guaranteed. In addition, the use of multiple sensors with associated evaluation leads to high costs and the need for mutual adjustment of the sensors.

Other approaches known from practice provide for the use of additional compensation electrodes which, with suitable wiring and dimensioning, can attenuate the influences of water and / or moisture in the stray field of the sensor. However, again complex adjustment measures are necessary.

The present invention is therefore based on the object, a sensor and a method of the type mentioned for detecting an approaching dielectric medium, preferably for the detection of a human body part, such and further, that a secure measurement regardless of environmental influences, especially moisture and / or water, with a simple design is guaranteed.

The inventive sensor for detecting an approaching dielectric medium solves the above object by the features of claim 1. Thereafter, such a sensor is characterized in that the capacitor with at least two different frequencies and / or at least two different duty cycles can be operated in sequence.

With regard to a method, the object mentioned is achieved by the features of claim 10. Hereinafter, a method for detecting an approaching dielectric medium is characterized in that the capacitor is operated with at least two different frequencies and / or at least two different duty cycles in sequence.

According to the invention it has been recognized that using a discharge method for capacitance measurement specific behaviors of individual dielectric Media against variable electric fields can be exploited. According to the invention it has also been recognized that in this way human body parts and various solids such as wood and polyethylene are distinguishable from water and / or moisture.

In the discharge method for capacitance measurement used according to the invention, the sensor is connected to a periodic, temporally variable voltage source and, during the times in which the output voltage supplied by the voltage source is substantially equal to zero, the charge is measured on the sensor. From this charge can be closed on the capacity of the sensor and occurring changes in this capacity can be detected. This clearly detectable entering into the stray field of the sensor dielectric media.

By changing the frequency and the duty cycle of the charging voltage, the time course of the electrical stray field emitted by the sensor changes. A duty cycle is understood to mean the quotient of the period duration and the pulse duration of a periodic, time-variable voltage. The duration of a pulse refers to that period of time in which a voltage surge with arbitrary time course assumes more than 50% of its amplitude.

In a stray field generated by voltages having different frequencies and / or duty cycles, different dielectric media exhibit different behaviors. Thus, the increase in capacitance of the sensor caused by a human body part is substantially constant over a wide frequency range. The same applies to different duty cycles. Many solids, such as wood and polyethylene, have a similar effect to a human body part. In contrast, water and / or moisture in the stray field of the sensor causes an increase in the capacitance of the sensor, which depends on the frequency used and / or the duty cycle used.

One reason for this is the dipole properties of the water. Since water forms permanent dipoles, orientation polarization can be observed in an electric field. Caused by an applied electric field the individual dipoles aligned by overcoming their inertia. The degree of alignment depends on the frequency and duration of the applied field. The higher the frequency chosen, the lower the reaction (orientation) of the dipoles or the higher the heat development. The shorter the duration of a pulse, the higher the likelihood that a dipole can not be completely aligned.

Utilizing this effect, a classification of the dielectric media passing into the stray field of the sensor can be made. For this purpose, a group of measurements is carried out, which consists of at least two measurements with at least two mutually different frequencies and / or at least two mutually different duty cycles. In this case, the period of time for carrying out the measurements is advantageously chosen such that any parameter changes which occur are negligible, for example due to changes in the distribution of moisture or temperature. Preferably, a group of measurements is repeated periodically.

Fig. 1

in einer schematischen Darstellung den prinzipiellen Aufbau eines Sensors zur Detektion eines sich nähernden dielektrischen Mediums in einer Frontansicht und

Fig. 2

in einer schematischen Darstellung den Schnitt A-A aus Fig. 1

There are now various possibilities for designing and developing the teaching of the present invention in an advantageous manner. For this purpose, on the one hand to the claims 1 and 11 subordinate claims on the other hand, to refer to the following explanations of a preferred embodiment of the invention with reference to the drawings. In the drawing shows

Fig. 1

in a schematic representation of the basic structure of a sensor for detecting an approaching dielectric medium in a front view and

Fig. 2

in a schematic representation of the section AA Fig. 1

Fig. 1 and Fig. 2 show a schematic representation of a preferred embodiment of the present invention from various views. In this case, the capacitor 1 forming the sensor is formed by two spaced-apart wires 2, 3, which are preferably arranged substantially in parallel. Instead of Wires can be used all comparable conductive structures known to the person skilled in the art, such as, for example, vapor-deposited or glued-on conductor tracks, conductive polymer layers or the like. Preferably, the wires 2, 3 in the seal of a window, a tailgate, a sliding door or similar, motorized moving parts of a motor vehicle are integrated. In general, however, the device according to the invention can be used to protect all electrically, pneumatically, hydraulically or in a comparable manner moving components in which the risk of pinching exists. Thus, it would be conceivable to equip a department store revolving door with the device according to the invention and to stop the rotational movement of the door in a pinching situation and if necessary to change the direction of rotation for a short time.

The wires forming the capacitor 2, 3 are preferably applied by a not shown voltage source with a square wave voltage whose frequency is preferably adjustable between 100 kHz and 10 MHz. In principle, even higher frequencies would be conceivable. In addition, the voltage in their duty cycle is adjustable, wherein the frequency and the duty cycle are preferably independently adjustable. As a result, a time-varying electrical stray field 4 is generated in the capacitor 1 and in its edge region, whose field lines in the Fig. 1 and 2 are drawn. In this stray field 4 is a schematically illustrated dielectric medium 5, which increases the capacitance of the sensor. This may be, for example, water, moisture, a human body part, a solid such as wood or polyethylene.

During a measurement, the sensor is charged with this square-wave voltage and then, at a certain time interval, the charge on the capacitor is measured. The measurements are performed with at least two different frequencies and / or duty cycles of the charging voltage and preferably repeated periodically.

From the measured charge it is concluded that the capacitance of the sensor is determined and changes in capacitance with respect to values from previous groups of measurements. Are these changes in all measurements within the current Group substantially the same, it is concluded that there is a human body part and / or a solid in the immediate vicinity of the sensor. If the changes in all measurements within the current group are different, then it is concluded that there is water and / or moisture in the area of the sensor, for example due to rain and / or wet seals.

Finally, it should be noted that the above-discussed embodiment merely explains the claimed teaching, but does not restrict it to the exemplary embodiment.

Claims (15)

1. Sensor using the capacitive measuring principle, for detecting an approaching dielectric medium (5), preferably for detecting a human body part, for use in a trapping protector, having a capacitor (1) and an electronic evaluation system, the change in the capacitance of the capacitor (1) brought about by the medium (5) being measurable,
   characterised in that the sensor carries out a group of measurements with at least two measurements in succession,
   the capacitor (1) being operated with at least two different frequencies and/or at least two different mark-to-space ratios during those at least two measurements.
2. Sensor according to claim 1, characterised in that the capacitor (1) is formed by two wires (2, 3) or comparable conductive structures arranged spaced apart from each other,
   the wires (2, 3) being arranged substantially in parallel.
3. Sensor according to claim 2, characterised in that the wires (2, 3) are fitted at the edge regions of a region of parts driven electrically, pneumatically, hydraulically or in a comparable manner, which region is critical in respect of a trapping situation, and/or
   in that the wires (2, 3) are integrated in the seal of a window, tailgate, sliding door or similar motor-driven parts of a motor vehicle.
4. Sensor according to any one of claims 1 to 3, characterised in that the capacitor (1) can be acted upon by a periodic voltage which is variable with time.
5. Sensor according to claim 4, characterised in that the voltage is a square wave voltage.
6. Sensor according to claim 4 or 5, characterised in that the voltage is adjustable in respect of its frequency, preferably between 100 kHz and 10 MHz.
7. Sensor according to claim 5 or 6, characterised in that the voltage is adjustable in respect of its mark-to-space ratio.
8. Sensor according to claims 6 and 7, characterised in that the frequency and the mark-to-space ratio may be adjustable independently of each other.
9. Sensor according to any one of claims 1 to 8, characterised in that the charge of the capacitor (1) is measurable.
10. Method for detecting an approaching dielectric medium (5), preferably for detecting a human body part, for use in a trapping protector, using a sensor according to any one of claims 1 to 9, having a capacitor (1) and an electronic evaluation system, the change in the capacitance of the capacitor (1) brought about by the medium (5) being measured,
    characterised in that the sensor carries out a group of measurements with at least two measurements in succession, the capacitor (1) being operated with at least two different
    frequencies and/or at least two different mark-to-space ratios during those at least two measurements.
11. Method according to claim 10, characterised in that the capacitor (1) is charged with a square wave voltage.
12. Method according to claim 10 or 11, characterised in that the change on the capacitor (1) is measured and/or
    in that the changing of the capacitor (1) and the measurement of the charge are carried out with a time interval with respect to each other.
13. Method according to any one of claims 10 to 12, characterised in that the group of measurements with at least two measurements is carried out with in each case mutually differing frequencies and/or mark-to-space ratios of the charge voltage,
    it being possible to effect all of the measurements of a group within such a short time frame that fluctuations of individual parameters are negligible.
14. Method according to any one of claims 10 to 13, characterised in that the group of measurements is repeated periodically and/or
    in that the capacitance of the capacitor (1) is inferred from the measured charge.
15. Method according to any one of claims 10 to 14, characterised in that it is inferred that water has been introduced into the field of the capacitor when the change in the capacitance brought about by the dielectric (5) assumes different values for all of the measurements within a group and/or
    in that it is inferred that a human body part has been introduced into the field of the capacitor when the change in the capacitance brought about by the dielectric (5) is substantially the same for all of the measurements within a group.

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