Capacitive sensor array and method for detecting actuation gestures at a motor vehicle

Abstract

A sensor array for detecting the approach and movement gestures of a user at a motor vehicle includes a capacitive sensor array and at least one control device that is coupled to the sensor array and detects a change in the capacitance of the sensor array. The sensor array includes at least two sensor electrode arrays which are arranged at spatially offset positions on the motor vehicle. The sensor electrodes are configured as elongate electrode arrays and are arranged with the same spatial orientation. The control and evaluation device is designed for cyclical activation and evaluation of the sensor electrodes with changeable, electrode-specific, different cycle rates.

Claims

1. A sensor arrangement for detecting the approach and movement gestures of a user at a motor vehicle, said sensor arrangement comprising: a capacitive sensor array and at least one control and evaluation device that is coupled to the sensor array and detects a change in the capacitance of the sensor array, wherein the sensor array comprises at least two sensor electrodes, which are arranged at spatially offset positions on the motor vehicle, the sensor electrodes being configured as elongate electrodes and being arranged with the same spatial orientation, wherein the control and evaluation device is designed for cyclical activation of the sensor electrodes in predetermined time intervals and to detect a change in the capacitance of each of the sensor electrodes, wherein the control and evaluation device is designed for the activation and evaluation of the sensor electrodes with changeable, electrode-specifically different cycle rates, wherein the control and evaluation device changes the cycle rate of the control and evaluation of individual electrodes as a function of the results of the evaluation at other electrodes.

2. The sensor arrangement according to claim 1, wherein one of the electrodes is able to be activated and evaluated by the control and evaluation device as a primary sensor electrode with a first cycle rate, and at least one secondary electrode is able to be activated as a function of the evaluation of the signals of the primary sensor electrode with a lower second cycle rate.

3. The sensor arrangement according to claim 2, wherein the control and evaluation device is designed for the reduction of the cycle rate of the activation of the secondary electrodes for the case where the evaluation of the primary sensor electrode indicates no actuation for a predetermined period of time.

4. The sensor arrangement according to claim 2, wherein the primary sensor electrode is arranged at a smaller distance from a monitored detection zone than the secondary sensor electrodes.

5. The sensor arrangement according to claim 1, wherein at least one of the sensor electrodes is arranged in a bumper of a motor vehicle.

Description

(1) The invention is now explained in further detail with the aid of the attached figures.

(2) FIG. 1a shows the arrangement of a first embodiment of the sensor array according to the invention on a motor vehicle;

(3) FIG. 1b shows the arrangement of FIG. 1 in a diagrammatic top view;

(4) FIG. 1c shows the arrangement from FIGS. 1a and 1b in a diagrammatic top view with illustrated detection zones;

(5) FIG. 2 shows a diagrammatic presentation of a signal sequence of two sensor electrodes;

(6) In FIG. 1a the rear of a vehicle 1 is shown. A sensor electrode array 2 is arranged in the region of the rear bumper. Beneath the sensor electrode array 2 (i.e. at a small height from the ground) a further sensor electrode 3 is arranged. The sensor electrodes 2 and 3 are connected respectively with a control- and evaluation device 5 (see FIG. 1B). The latter is coupled, in turn, with a central vehicle control unit 4, which controls and releases an opening of the tailgate of the vehicle. The electrodes are charged via the device 5 and the capacitance change of the electrodes, on the approach of a body, e.g. of a body part of the operator, can be detected by charge evaluation. This principle of a capacitive sensor is known in the field of motor vehicle technology.

(7) The sensor electrode array 3 runs substantially parallel to the electrode 2. The electrodes 2 and 3 are constructed here continuously with substantially constant sensitivity. One or both of the electrodes could, however, also be constructed as segmented electrodes, the detection sensitivity of which varies in longitudinal direction, i.e. has regions with varying detection sensitivity in the direction of the extent of the bumper.

(8) When wishing to carry out an operation, an operator can move his lower leg in a swinging movement under the bumper. This movement and approach is detected both by the electrode array 2 and also by the sensor electrode 3, as the capacitance change is interrogated repeatedly chronologically, and the change is evaluated. A capacitance is determined by each of the electrodes by repeated interrogation. In this example, the frequency of the interrogation can be 30 Hz initially for all electrodes. In each of the electrodes, however, the operation will bring about signal responses which are different chronologically and with regard to amount.

(9) A time sequence of capacitance values, which the evaluation device 5 collects, is evaluated for the detection of characteristic features of an operating gesture. When both the signal sequences of the electrode 2 and also those of the electrode 3 show the characteristic values, a signalling takes place to the control unit 4. The latter registers the operating gesture and initiates an interrogation of an authorisation. In the course of this, ID transmitters, which an authorized user carries on his person, are interrogated in the environment of the vehicle. If such an ID transmitter with access authorization is detected and successfully interrogated, the opening of the boot lid is initiated.

(10) If, however, the vehicle is locked and in addition no signal response which indicates an operation of this electrode 3 has been registered for a lengthy period of time, in this example for more than six hours, the control- and evaluation device 5 changes into a first energy-saving mode. In this first mode, the electrode 3 is still interrogated with 30 HZ, however the electrode 2 is only interrogated with 5 Hz. This reduced frequency reduces the necessary energy supply into this electrode and nevertheless ensures that the control- and evaluation device 5 receives five values per second from this electrode. On the basis of these values, a continuously updated calibration of this electrode can take place. If, for example, a rainfall begins around the parked car, the capacitance values of the electrodes will change, but so slowly that a calibration can be updated without any problems. The calibration takes place e.g. by the formation of a sliding mean value over the last 25 detected values (5 seconds). This mean value can be subtracted as offset from the current measurement values.

(11) If no operation is detected at the electrode 3 for a further considerable longer time, e.g. three days (and the vehicle is also not unlocked by other access possibilities, e.g. via the vehicle doors), the detection frequency both of the electrode 3 and also of the electrode 2 can be further reduced. For example, the interrogation frequency for the electrode 3 is reduced to 10 Hz and the frequency of the electrode 2 remains at 5 Hz. In this case, however, in the case of an operation without prior notification to the vehicle (e.g. via ID transmitter), it can be necessary that an operating gesture has to be carried out several times, because firstly the electrode array has to be alerted. Nevertheless, the electrodes are in a calibrated state at all times, even when the detection cycle time is reduced.

(12) FIG. 1C shows the arrangement from another view. Here, the detection area 3a of the electrode 3 and the detection area 2a of the electrode 2 are illustrated. The lower leg 6 of an operator is shown symbolically. From this illustration, it can be seen that the operator is already situated in the detection area 2a, but not in the detection area 3a. If the operator 6 were a passer-by, this approach would not yet lead to an alerting of the sensor electrodes, because in this example the electrode 3 is constructed as wake-up or trigger electrode, as its accidental or undirected triggering is less likely than in the case of electrode 2. Which electrode is to act, however, as high clocked trigger electrode can be established by determining various interrogation modes in the on-board system, depending on whether maximum energy saving or maximum detection readiness is desired. If the electrode 2 is selected as wake-up electrode, then this indicated approach will lead to an alerting of all sensor electrodes, wherein the electrodes, which are calibrated at all times, are immediately detection-ready.

(13) FIG. 2 shows an abstracted possible signal sequence for a sensor array with two sensor electrodes. The signal strengths or capacitances are represented along a time axis t.

(14) The signals of the electrode 3 are represented in the background (lighter hatching), whereas the signals of the electrode 2 are shown in the foreground (stronger hatching).

(15) Firstly, both electrodes are interrogated with the same frequency. At the time t1 a waiting time Mt after locking the vehicle has elapsed, and the interrogation frequency of the electrode 2 is reduced to a third with respect to the frequency of the electrode 3. The energy consumption of the system is thereby reduced.

(16) At t2, the environmental conditions of the array change, e.g. it begins to rain. The offset values for both electrodes increase, taken into consideration, however, by a continuous calibration at both electrodes. Since also the electrode 2, even though with lower frequency, is interrogated, the calibration is included and the offset is updated at all times for a detection of an actuation. The sliding averages, which are calculated at all times for both electrodes, are represented by way of example.

(17) It can be seen that at t3 in the electrode 2 a significant signal change occurs. As this electrode, however, is not the wake-up electrode and no significant change is detected at electrode 3, the electrode 3 remains in the cycle-reduced mode. This procedure can be brought about e.g. by a pedestrian who moves past the vehicle.

(18) At time t4, the electrode 3 shows a significant change, which could indicate an actuation. The cycle time of the interrogation of electrode 2 is immediately increased, in order to be able to detect an actuation. With a successful interrogation, the opening of boot is activated by the central control device.