WO2014000891A2

WO2014000891A2 - Capacitive sensor for a collision protection device

Info

Publication number: WO2014000891A2
Application number: PCT/EP2013/001903
Authority: WO
Inventors: Florian Pohl; Holger WÜRSTLEIN; Detlef Russ; Ralf Daiminger
Original assignee: Brose Fahrzeugteile Gmbh & Co.
Priority date: 2012-06-28
Filing date: 2013-06-28
Publication date: 2014-01-03
Also published as: DE102012012865A1; WO2014000891A3

Abstract

The invention relates to a capacitive sensor (2) for detecting an object, in particular for detecting the event of a collision in a mobile vehicle part. The sensor (2) comprises an electrode array (4) having at least one sensor electrode (6). The sensor (2) further comprises a signal generating circuit (7) located upstream of the at least one sensor electrode (5) for generating a transmission signal (S_E), wherein the signal generating circuit (7) generates the transmission signal (S_E) as a pulse signal having a trapezoid or triangular temporal pulse shape.

Description

description

Capacitive sensor for a collision protection device

The invention relates to a capacitive sensor for detecting an object, in particular a body part of a person or an object, and to a collision protection device with such a sensor.

Capacitive sensors are used in vehicle technology, in particular in the context of a collision protection device. Such a collision protection device is generally used to detect an obstacle in an opening portion of a vehicle part, which is movable relative to a fixed frame between an open position and a closed position. The vehicle part to be monitored may also be a side door, a trunk or engine compartment flap, a sunroof or a folding roof. when the respectively associated adjusting element is moved by a motor.

The opening area is the space through which the adjustment element passes during an adjustment movement. The opening region of the adjusting element particularly includes the space region which is arranged between a closing edge of the adjusting element and a corresponding edge of the frame, against which the adjusting element rests in the closed position with its closing edge.

When closing adjusting elements of a vehicle, in particular a tailgate, there is often the risk that body parts or other objects between the closing edge of the adjusting element and the body are clamped. The collision protection device, which is also referred to as anti-pinch device in this application, serves to avoid such a trapping case and the resulting risk of personal injury.

CONFIRMATION COPY and / or material damage, in that the collision protection device detects obstacles in the opening area and in this case stops or reverses the closing movement.

Furthermore, a collision protection device can also be used to detect obstacles that are in the way of the opening of the adjustment element. Also in this application, the collision protection device stops or reverses the movement of the adjustment when it detects such an obstacle to avoid damage to property due to a collision of the adjustment with the obstacle.

A distinction is made between indirect and direct collision protection devices. An indirect collision protection device detects the collision case (in particular Einklemmfall) based on monitoring an operating variable of the adjusting element driving servomotor, in particular an abnormal increase in the motor current or an abnormal decrease in the engine speed.

By contrast, a direct collision protection device usually comprises one or more sensors which detect a measured variable which is characteristic for the presence or absence of an obstacle in the opening region, and an evaluation unit which uses this measured variable to decide whether an obstacle is present in the opening region and, if appropriate, triggers appropriate countermeasures. Among the direct collision avoidance devices, a distinction is again made between systems with so-called touch sensors, which only detect the presence of an obstacle when the obstacle already touches the sensor, and systems with contactless sensors, which detect an obstacle already at a certain distance from the sensor. Non-contact sensors include in particular so-called capacitive (proximity) sensors.

A capacitive sensor comprises an electrode arrangement with one or more electrodes, via which an electric field is built up in the opening region of the adjusting element. An obstacle in the opening area is by monitoring recognized the capacity of the electrode assembly. In this case, use is made of the fact that an obstacle, in particular a human body part, influences the electric field generated by the sensor, and thus the capacitance of the electrode arrangement.

In a conventional design of such a capacitive sensor, the electrode arrangement of this sensor comprises at least one transmitting electrode, which is connected to a signal generating circuit, and a receiving electrode, which is connected to a receiving circuit (transmitter-receiver principle). Such a sensor measures the capacitance formed between the transmitting electrode and the receiving electrode or a measured variable correlating therewith.

In an alternative design, the electrode arrangement of a capacitive sensor comprises only one sensor electrode or a plurality of similar sensor electrodes, which are acted upon by the transmission signal, and via which also the capacity-dependent reception or response signal, e.g. in the form of the displacement current, is detected (one-electrode principle). In such a sensor, a sensor external, assepotential object is used as the counter electrode, in particular the body of the vehicle in which the sensor is installed. In such a sensor, the capacitance of the sensor electrode (s) is thus detected as mass to mass.

An intended for monitoring the opening area of a tailgate collision protection device or anti-trap device with a capacitive sensor is known from DE 20 2007 008 440 U1.

As a transmission signal, a sinusoidal electrical alternating signal is usually used, which oscillates at a predetermined transmission frequency. Disadvantageously, the generation of such a sinusoidal signal requires a comparatively complicated circuit technique. Alternatively, a square-wave pulse signal is sometimes used as the transmission signal, which can be generated much less expensively by a simple switching element. However, such a rectangular pulse signal disadvantageously complies with a high harmonic content and is thus critical with respect to the electromagnetic compatibility (EMC) of the sensor. The invention has for its object to provide an electromagnetically acceptable, but at the same time particularly simple capacitive sensor and a collision protection device with such a sensor.

With respect to the sensor, the above object is achieved by the features of claim 1. With respect to the collision protection device, the object is achieved by the features of claim 7. Advantageous embodiments and further developments of the invention are the subject of the dependent claims.

The sensor according to the invention comprises an electrode arrangement which comprises at least one sensor electrode. The sensor further comprises a signal generating circuit, which is connected upstream of the at least one sensor electrode and which serves to generate a transmission signal for this sensor electrode (s). According to the invention, the signal generation circuit generates the transmission signal as a pulse signal having a trapezoidal or triangular time pulse shape.

In this case, a triangular pulse form denotes a signal course in which the signal strength-in particular the electrical voltage-of the transmission signal in each pulse proceeds at least approximately linearly with time up to a maximum (or minimum) signal value, starting from a minimum (or maximum) signal value rises (or falls), and immediately thereafter at least approximately linearly decreases (or increases) with time to a minimum (or maximum) signal value.

In contrast, a waveform is referred to as a trapezoidal pulse shape in which the signal strength in each pulse rises (or decreases) from at least approximately linear with time to a maximum (or minimum) signal value a given plateau time remains at least approximately constant, and only then again at least approximately linearly decreasing (or increasing) with time to a minimum (or maximum) signal level.

The transmission signal is preferably symmetrically offset with respect to a change of sign. In this case, in the case of a triangular pulse shape, the pulses adjoin one another directly in time, while in the case of the trapezoidal pulse shape, two successive pulses are separated by an impulse time corresponding to the plateau time. In the context of the invention, however, the pulses of the transmission signal may also be separated by longer interpulse times.

The generation of the transmission signal as a triangular or trapezoidal pulse signal has the advantage that the transmission signal on the one hand - as a rectangular pulse signal - can be generated by simple switching. In contrast to a square-wave pulse signal, however, the transmission signal according to the invention again has the advantage that it has only comparatively weak harmonic components, which has a positive effect on the electromagnetic compatibility of the sensor.

The invention can basically be applied to capacitive sensors operating on the one-electrode principle, which sense the capacitance of their sensor electrode (s) to ground. Preferably, however, the sensor is a capacitive sensor which operates according to the transmitter-receiver principle. Accordingly, the electrode arrangement preferably comprises at least one transmitting electrode and at least one receiving electrode as sensor electrodes. The signal generating circuit is connected upstream of the at least one transmitting electrode.

In preferred dimensioning, the signal generation circuit generates the transmission signal in particular as a result of pulses whose edge rise time and / or flank descent time correspond to at least 1%, preferably at least 5%, in particular at least 10% of the total period duration. The period duration corresponds to the time that elapses between the start (or end) of a pulse and the beginning (or end) of the next pulse. The period duration thus includes the (temporal) pulse length as well as an optional interpulse time formed between two pulses. In a particularly simple design, the signal generating circuit is essentially formed by a switching element and a downstream amplifier circuit. In this case, the switching element serves to generate a rectangular pulse signal which is converted by the amplifier circuit into the - triangular or trapezoidal - transmission signal. The amplifier circuit is limited in this case according to the desired pulse shape of the transmission signal, thus has a correspondingly low slew rate. In a preferred embodiment, the amplifier circuit is designed as an integrator.

In an expedient embodiment variant, the sensor comprises a microcontroller. In this case, a digital output of the microcontroller is preferably used as a switching element for generating the square-wave pulse signal.

The collision protection device according to the invention comprises a capacitive sensor of the type described above.

Hereinafter, embodiments of the invention will be described with reference to a drawing. Show:

1 is a schematic block diagram of an anti-pinch device for detecting and avoiding a trapping case in a movable vehicle part, comprising a capacitive sensor comprising a transmitting electrode, a receiving electrode, a signal generating circuit connected upstream of the transmitting electrode, and a receiving circuit connected downstream of the receiving electrode,

2 shows in a simplified electrical circuit diagram the construction of the signal generation circuit, which is formed here by a microcontroller having a digital output serving as a switching element for generating a rectangular pulse voltage and by a downstream integrator, as well as FIGS. 3 and 4 show two variants of a transmission signal which can be generated by means of the signal generation circuit according to FIG. 2.

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

Fig. 1 shows a schematic representation of an anti-trap device 1 for a (not shown) movable adjusting a motor vehicle, in particular a motorized door or tailgate. The anti-pinch device 1 comprises a capacitive sensor 2 and a monitoring unit 3.

The sensor 2 is based on a capacitive measuring technique. The sensor 2 comprises an electrode arrangement 4 with at least one transmitting electrode 5 and at least one counterelectrode or receiving electrode 6. The electrode arrangement 4 preferably comprises (not shown in detail) a plurality of transmitting electrodes 5 which interact with a common receiving electrode 6.

During operation of the sensor 2, an electrical field F (merely indicated) is generated in an opening region of the adjusting element by application of an alternating electrical voltage to the or each transmitting electrode 5, while via the receiving electrode 6 the (electrical) capacitance of the field emitting transmitting electrode 5 and the Receiving electrode 6 formed capacitor is detected.

More specifically, in addition to the electrode assembly 4, the sensor 2 includes a signal generating circuit 7, a receiving circuit 8, and a capacitance measuring element 9.

In the operation of the sensor 2, the signal generating circuit 7 generates a transmission signal SE in the form of a pulse signal. The signal generation circuit 7 outputs the transmission signal SE to the transmission electrode 5, which, under the action of the transmission signal S _E the electric field F emitted. If the sensor 2 comprises a plurality of transmitting electrodes 5, the signal generating circuit 7 and the electrode arrangement 4 are preferably interposed by a time multiplexer (not illustrated), which alternately outputs the transmitting signal SE to one of the plurality of transmitting electrodes 5 in each case.

Under the action of the electric field F, an electrical alternating signal is generated in the receiving electrode 6, which is referred to below as the received signal SR. The received signal SR is phase-synchronized with the transmission signal SE, thus having defined pulse edges between a high signal level and a low signal level, which coincide with the pulse edges of the transmission signal SE in time. In contrast to the transmission signal SE, the signal amplitude of the reception signal SR additionally varies depending on the capacitance to be measured.

The received signal SR is supplied to the receiving circuit 8 as an input signal. In this case, the receiving electrode 6 and the receiving circuit 8 are optionally interposed with a low-pass filter (not explicitly shown) for prefiltering the received signal SR. The receiving circuit 8 is designed for example as a transimpedance amplifier. In this embodiment, the receiving circuit 8 outputs a voltage signal, hereinafter referred to as the received signal SR ', which is proportional to the displacement current induced in the receiving electrode 6 under the effect of the transmission signal SE. This received signal SR 'is fed to the capacitance measuring element 9 connected downstream of the receiving circuit 8, which generates a capacitance-proportional measured variable K from this.

The measured variable K is supplied to the sensor 2 downstream monitoring unit 3. The monitoring unit 3, which is preferably formed by a microcontroller with monitoring software implemented therein, compares the measured variable K with a stored trigger threshold value. If the threshold value is exceeded, the monitoring unit 3 outputs a triggering signal A which indicates a possible trapping case, and under whose effect the motion tion of the anti-trap device 1 associated adjustment is reversed.

The transmission signal SE is not an ordinary rectangular pulse signal but has a pulse signal with non-negligible temporal signal rise and fall regions, wherein the signal value in these ranges changes at least approximately linearly over time. In order to generate this transmission signal SE, the signal generation circuit 7 according to FIG. 2 comprises a microcontroller 20 and an electronic integrating circuit downstream of it (hereinafter integrator 21). The integrator 21 is itself formed by an operational amplifier 22, an input resistor 23, which is connected upstream of the inverting input of the operational amplifier 22, a coupling capacitor 24, via which the output of the operational amplifier 22 is fed back to the inverting input, and a coupling capacitor 24 in parallel coupling resistance 25. The non-inverting input of the operational amplifier 22 is connected to ground M.

The integrator 21 is itself formed by an operational amplifier 22, an input resistor 23, which is connected upstream of the inverting input of the operational amplifier 22, a coupling capacitor 24, via which the output of the operational amplifier 22 is fed back to the inverting input, and a coupling capacitor 24 in parallel coupling resistance 25. The digital output 26 is used as a switching element for generating a rectangular pulse signal R by the microcontroller 20 under the action of a control program implemented therein the digital output 26 temporally alternating (in particular periodically) between a high voltage value (eg + 5V) and a low voltage value (eg -5V). The non-inverting input of operational amplifier 22 is connected to ground M (0V) or other reference potential located midway between the voltage values of the rectangular pulse signal R. The vertical, ie temporally instantaneous, rising and falling edges of the rectangular pulse signal R are ground by the downstream integrator 21 into "oblique", ie temporally linear rise and fall, edges of the transmission signal SE. flanks is determined by the circuitry dimensioning of the integrator 21. In suitable dimensioning, for example, the input resistor 23 has an amount of 1 kQ, the coupling capacitor 24 an amount of 100nF and the coupling resistor 25 an amount of 1 Ω.

The resulting signal form of the transmission signal SE can hereby be specified by specifying the frequency, and thus the period P (FIG. 3), of the rectangular pulse signal R. If this period P is chosen to be greater than twice the rising edge time tR (FIG. 3) of the transmission signal SE, the result is a trapezoidal pulse shape for the transmission signal S _E , which is shown by way of example in FIG. 3 in a diagram of the transmission signal SE versus time t , Otherwise, the transmission signal SE assumes a triangular pulse shape which is shown by way of example in FIG. 4. The period P, with which the microcontroller 20 generates the square-wave pulse signal, can be fixed by the control program implemented in the microcontroller 20. Alternatively, it can be provided that the period P - by parameterization of the control program or automatically in response to the microcontroller 20 supplied environment variables - is implemented variable (ie in the form of a program variable).

As can be seen from FIG. 3, in the case of a trapezoidal pulse shape, each pulse 27 of the transmission signal SE has a rising edge 28, a falling edge 29 and a plateau 30 formed therebetween, wherein in the rising edge 28 the signal value of the transmitting signal SE within the rising edge time tR is temporal increases linearly from zero to a maximum value,

in plateau 30, the signal value remains constant at the maximum value for the duration of a plateau time tp, and

within the falling edge 29, the signal value within a fall time t, F again falls linearly from the maximum value to zero in time.

In this case, the pulses 27 are each time-symmetrical, so that the edge fall time t _F corresponds to the edge rise time t _{R in} terms of size. The entire pulse duration D thus results from the sum of the edge rise time t _R , the plateau time t _P and the edge fall time tF. Between each two successive pulses 27, an interpulse time ti is formed, which corresponds to the size of the plateau time t _R , and in sum with the pulse duration D results in the period P.

As can be seen from the comparison of FIGS. 3 and 4, the triangular pulse shape of the transmission signal SE according to FIG. 4 follows from the trapezoidal pulse shape according to FIG. 3 for the special case that the plateau time t _P and the interpulse time ti go to zero.

By appropriate design of the integrator 21 and the control program implemented in the microcontroller 20, it is ensured that the edge rise time t _R and the edge fall time t _F respectively correspond to at least 10% of the period P. In particular, it is provided that the ratio of the edge rise time t _R or edge fall time t _F to the period between 10% and 50% can be selected by correspondingly variable setting of the period P in the microcontroller 20.

Although the invention will be particularly apparent from the embodiment described above, it is not limited thereto. Rather, other embodiments of the invention may be derived by those skilled in the art from the foregoing description. In particular, the microcontroller 20 (or the control program implemented therein) and the integrator 21 may be designed such that the transmission signal S _E output from the signal generation circuit 7 is asymmetrical in that the edge rise time t _{R is} from the edge fall time t _F and / or the Plateau time tp can differ from the interpulse time ti. Furthermore, completely equivalent to the above description, the pulses 27 may also be defined as negative pulses, in which case each pulse starts with a falling edge and ends a rising edge.

In contrast to the embodiment described above, in which the signal generating circuit 7 includes its own microcontroller 20, the function of this microcontroller 20 can also be used in the microcontroller of another integrated device. In particular, it is provided in an expedient embodiment variant that the monitoring unit 3 and the signal generation circuit 7 share a common microcontroller.

Furthermore, both in the case of the signal generating circuit 7 and in the case of the monitoring unit 3, the microcontroller can also be replaced by a non-programmable hardware circuit, for example an ASIC.

LIST OF REFERENCE NUMBERS

1 anti-trap device

2 sensor t _F slope descent time

3 monitoring unit tl interpulse time

4 electrode arrangement tp plateau time

5 Transmitting electrode t _R Flank attack time

6 receiving electrode A trip signal

7 Signal generation circuit D Pulse duration

8 receiving circuit F (electric) field

9 Capacitance measuring element K Capacitance measured variable

20 microcontroller M ground

21 Integrator P Period

22 operational amplifier R Rectangular pulse voltage

23 input resistance S _E transmission signal

24 coupling capacitor SR received signal

25 coupling resistor SR. receive signal

26 digital output

27 pulse

28 rising edge

29 waste edge

30 plateau

Claims

claims

1. Capacitive sensor (2) for detecting an object, in particular for detecting a collision case in a movable vehicle part,

with an electrode arrangement (4) which comprises at least one sensor electrode (6),

- With one of the at least one sensor electrode (5) upstream signal generating circuit (7) for generating a transmission signal (SE), wherein the signal generating circuit (7) generates the transmission signal (SE) as a pulse signal having a trapezoidal or triangular temporal pulse shape.

2. Sensor (2) according to claim 1,

- Wherein the electrode assembly (4) as sensor electrodes at least one transmitting electrode (5) for emitting an electric field (F) under exposure to the transmission signal (SE) and at least one receiving electrode (6), and

- Wherein the receiving electrode (6) a receiving circuit (8) for processing in the receiving electrode (6) under the action of the electric field (F) generated received signal (SR) is connected downstream.

3. Sensor (2) according to claim 1 or 2,

wherein the signal generation circuit (7) generates the transmission signal (SE) as a sequence of pulses (27) having a period (P) and an edge rise time (tR) and a slope descent time (tF), wherein the edge rise time (t _R ) and / or the edge descent time (if) at least 1%, preferably at least 5%, in particular at least 10% of the period (P) correspond.

4. Sensor (2) according to claim 3,

wherein the signal generating circuit (7) comprises a switching element (26) for generating a rectangular pulse signal (R) and a downstream amplifier circuit (21) for converting the rectangular pulse signal (R) in the transmission signal (SE).

5. Sensor (2) according to claim 4,

wherein a digital output (26) of a microcontroller (20) is used as switching element.

6. Sensor (2) according to claim 4 or 5,

wherein the amplifier circuit is designed as an integrator (21).

7. collision protection device (1) with a capacitive sensor (2) after

of claims 1 to 6.