Sensor system with at least one capacitive sensor and method for operating a sensor system

Abstract

Sensor system for securing moving objects, in particular motor-operated doors (10) or flaps, comprising at least one capacitive sensor (16), wherein the capacitive sensor has at least one first electrode, and comprising at least one control unit (18a, 18b), wherein the control unit (18a, 18b) is configured to generate a first transmit signal for the at least one capacitive sensor (16) and to evaluate a first received signal (S1) from the at least one capacitive sensor (16), characterized by at least one further separate second electrode (20) spatially separated from the sensor (16), wherein the at least one capacitive sensor (16) and the at least one further second electrode (20) are movable relative to each other, and wherein means for generating a second transmit signal for the at least one further second electrode, wherein the first transmit signal and the second transmit signal are either different or time-shifted relative to each other,and / or means for evaluating a second received signal (T1) from at least one further second electrode (20) are provided, wherein the first received signal (S1) and the second received signal (T1) are different.

Description

[0001] The invention relates to a sensor system for securing moving objects, in particular motor-operated doors or flaps, comprising at least one capacitive sensor, wherein the capacitive sensor has at least one first electrode, and at least one control unit, wherein the control unit is configured to generate a first transmit signal for the at least one capacitive sensor and to evaluate a first received signal from the at least one capacitive sensor. The invention also relates to a method for operating a sensor system according to the invention.

[0002] German patent application DE 10 2008 005 783 A1 discloses a moisture-independent capacitive pinch protection device. The pinch protection device comprises a capacitive sensor and a control unit. The control unit is configured to generate a transmit signal for the at least one capacitive sensor and to evaluate a first received signal from the at least one capacitive sensor.

[0003] German patent application DE 10 2008 035 634 A1 discloses a switching strip for obstacle detection. The switching strip has an extruded profile, comprising a first conductive area with an embedded wire strand and a second electrically conductive area with an embedded wire strand. The first and second electrically conductive areas are spaced apart. The switching strip profile is designed for capacitive pinch protection.

[0004] German patent application DE 10 2007 026 307 A1 discloses a capacitively operating anti-pinch device. It provides a transmitting electrode device for emitting an alternating field into an emission area and a receiving electrode device for detecting an alternating field present in a detection area.

[0005] German patent DE 103 10 066 B3 describes a device for detecting an obstacle in the opening area of ​​a movable locking element. The device comprises a sensor electrode and a base electrode, as well as a control unit connected to the sensor electrode and the base electrode. The sensor electrode and the base electrode generate an electric field in the opening area of ​​the locking element. The evaluation unit detects a capacitive change in the electric field caused by the presence of an obstacle in the opening area of ​​the locking element and provides at least one control signal for a drive that moves the locking element.

[0006] The invention aims to improve a sensor system and a method for operating a sensor system for securing moving objects with at least one capacitive sensor.

[0007] According to the invention, a sensor system with the features of claim 1 and a method for operating a sensor system with the features of claim 11 are provided. Advantageous embodiments of the invention are specified in the dependent claims.

[0008] A sensor system for securing moving objects, in particular motorized doors or flaps, comprises at least one capacitive sensor, wherein the capacitive sensor has at least one first electrode, and at least one control unit. The control unit is configured to generate a first transmit signal for the at least one capacitive sensor and to evaluate a first received signal from the at least one capacitive sensor. At least one further second electrode, separate from the sensor, is provided, wherein the at least one capacitive sensor and the at least one further second electrode are movable relative to each other. Means for generating a second transmit signal for the at least one further second electrode are provided, wherein the first transmit signal and the second transmit signal are either different or time-shifted from each other.Alternatively or additionally, means for evaluating a second received signal from at least one further second electrode are provided, wherein the first received signal and the second received signal are different. The control unit can include the means for evaluating a second received signal from the at least one further electrode. The evaluation means are configured to derive information about the distance between the at least one capacitive sensor and the further second electrode from the second received signal.

[0009] By providing a second electrode and evaluating the second received signal from at least one additional second electrode, information about the distance between the capacitive sensor and the second electrode is available. This distance information can be used to improve the capacitive detection of objects. Specifically, the received signal of a capacitive sensor changes when it is brought close to a ground or when the ground is brought close to the sensor. Thus, the received signal of a capacitive sensor mounted, for example, on the tailgate of a vehicle changes even without an object being present, simply by closing the tailgate.If additional distance information is available and the second electrode is, for example, fixed to the vehicle opposite the capacitive sensor on the tailgate, then the change in the capacitive sensor's received signal when the tailgate closes can be compensated for by the distance information or taken into account in another way. This allows for a significantly more reliable distinction between a change in the capacitive sensor's received signal due to a change in the distance between the capacitive sensor and ground simply from closing the tailgate, and a signal change caused by the presence of an object in the closing gap between the tailgate and the vehicle.In a surprisingly simple way, the invention enables a significant improvement in the capacitive detection of objects, particularly in the safety monitoring of motorized doors or flaps, such as tailgates, vehicle doors, sliding doors, sunroofs, machine enclosures with flaps, and the like. The sensor system according to the invention can also be used, for example, to monitor robot arms, for instance, to detect moving objects, such as people, within the range of motion of a robot arm.

[0010] In a further development of the invention, the control unit is designed to calculate a differential signal, wherein the differential signal is formed from the, optionally weighted, received signal of the at least one capacitive sensor and the, optionally weighted, received signal of the at least one further second electrode.

[0011] Such a differential signal is essentially independent of the distance between the sensor and the other electrode. For example, if the sensor is mounted on the closing edge of a door or flap, and the other electrode is mounted opposite the sensor in the closing direction on a housing, such as a vehicle body, the differential signal is essentially independent of the relative position of the door and the body and can therefore be used very easily to detect an object. The received signals from the capacitive sensor alone, and the received signal from the second electrode, provide information about the distance between the sensor and the second electrode, and thus also about the closed state of the door or flap.

[0012] In a further development of the invention, at least one further second electrode forms part of a second further capacitive sensor.

[0013] In this way, when using two capacitive sensors that are movable relative to each other, distance information can be obtained by using, for example, the received signal of the second capacitive sensor only temporarily to obtain information about the distance between the two capacitive sensors.

[0014] In a further development of the invention, at least two capacitive sensors are provided and the control unit is designed to apply a transmission signal to the capacitive sensors successively.

[0015] In this way, the two capacitive sensors can be used alternately as sensors and as an additional electrode. For example, one capacitive sensor emits a transmission signal during a first time interval, and the received signal from this capacitive sensor is then used to detect objects. During the first time interval, the second capacitive sensor is not subjected to a transmission signal and functions as an additional electrode. The received signal from the second capacitive sensor can then be used to determine the distance between the two capacitive sensors.

[0016] In a further development of the invention, at least two capacitive sensors are provided, wherein the control unit is configured to generate a transmission signal with a different frequency for each capacitive sensor.

[0017] In this way, the capacitive sensors can be operated simultaneously. The first capacitive sensor receives a transmission signal at a first frequency, and the second capacitive sensor uses the first frequency to determine the distance between the two capacitive sensors. The second capacitive sensor, however, receives a transmission signal at a second frequency and operates at this second frequency as an object detection sensor. At the second frequency, the first capacitive sensor acts as an additional electrode for determining the distance between the two capacitive sensors. Thus, both object detection and distance measurement are performed simultaneously by both sensors.This significantly improves both the detection of objects and the determination of the distance between the two capacitive sensors.

[0018] In a further development of the invention, the control unit has a memory and means for comparison, wherein at least one signal waveform of the received signal of the further second electrode and an associated distance between the capacitive sensor and the further second electrode is stored in the memory, and wherein the means for comparison compare the received received signal with the stored received signal in order to obtain information about the distance between the capacitive sensor and the further second electrode.

[0019] In this way, the distance information can be calibrated, and information about the distance between the closing edges of the door or flap is available at all times while a door or flap is closing.

[0020] In a further development of the invention, the control unit has means for learning and storing a signal profile of the received signal and the associated distance between the capacitive sensor and the further second electrode.

[0021] By learning and storing the signal profile of the received signal, local conditions and boundary conditions can be taken into account. For example, such learning can only take place in a vehicle after its completion and the installation of all optional equipment. However, the invention also allows the signal profile of the received signal to be repeatedly learned and stored during vehicle operation. This can be done as part of a functional check and does not necessarily have to cover the entire range of motion of the door or hatch, but can, for example, also be performed only in a critical range of motion immediately before the door or hatch is completely closed.Learning and saving a signal history of the received signal can also be done regularly, for example, when opening a door or flap, provided there is no risk of trapping a moving object, such as a human hand.

[0022] In a further development of the invention, the control unit has spatially distributed sub-control units, wherein each capacitive sensor and / or each further second electrode is assigned a sub-control unit, and wherein the sub-control units are each configured to generate a transmission signal, and wherein the sub-control units are synchronized at least with respect to generating the transmission signals.

[0023] This allows for short cable runs between the individual sensors and the control units. This is particularly advantageous for large doors or flaps, or, for example, for securing the movement area of ​​a robot arm. However, it is essential in such cases that the sub-control units are synchronized, at least with regard to generating the transmission signals.

[0024] In a further development of the invention, the sub-control units are each provided with a serial interface for communication with the other sub-control units.

[0025] In a method for operating a sensor system for securing moving objects, in particular motor-operated doors or flaps, with at least one capacitive sensor, wherein the capacitive sensor has at least one first electrode, with at least one control unit, wherein the control unit is configured to generate a first transmit signal for the at least one capacitive sensor and to evaluate a first received signal from the at least one capacitive sensor, and with a further second electrode spatially separated from the sensor, wherein the at least one capacitive sensor and the at least one further second electrode are movable relative to each other, the steps of evaluating a second received signal from the at least one further second electrode, wherein the first received signal and the second received signal are different, areand the derivation of information about the distance between the at least one capacitive sensor and the further second electrode from the second received signal.

[0026] By deriving information about the distance between at least one capacitive sensor and the second electrode, the detection of objects can be significantly improved, since the signal change caused solely by the approach of the capacitive sensor and the second electrode can be compensated for by means of the distance information.

[0027] In a further development of the invention, the formation of a difference signal from the first and the second received signal is provided.

[0028] Such a differential signal is essentially independent of the distance between the capacitive sensor and the second electrode, and can therefore significantly facilitate the detection of an object.

[0029] In a further development of the invention, the comparison of the second received signal of the receiving electrode with a stored profile of the second received signal is provided, wherein the stored profile is assigned a profile of the distance between the capacitive sensor and the receiving electrode.

[0030] In a further development of the invention, it is provided that a sequence of the second received signal and the associated distance is stored by means of a learning process.

[0031] In a further development of the invention, the generation of a second transmit signal for the at least one further second electrode and the application of the second transmit signal to the further second electrode and the evaluation of the first received signal from the at least one capacitive sensor are provided.

[0032] The transmit signal emitted by the second electrode is received by the at least one capacitive sensor. By evaluating this received signal, information about the distance between the second electrode and the at least one capacitive sensor can be obtained. The interference with the sensor signal can thus be compared with the distance information. In this way, interference from objects equipped with an electrode within the sensor's range can be compensated for. If two capacitive sensors are provided, both sensors can be simultaneously stimulated with a transmit signal. In this mode of operation, more sensitive object detection can be expected if both sensors are very close to each other. The interference with the sensors' received signal caused by their proximity can be compensated for by the information about the distance between the two sensors.Distance information can be obtained either through time-division multiplexing or by using different frequencies for the transmission signals from each sensor. The control unit must, of course, be able to evaluate all the frequencies used.

[0033] In a further development of the invention, the sensor system has at least two capacitive sensors, wherein the application of the first transmission signal to the two capacitive sensors is provided sequentially.

[0034] In this way, at least one capacitive sensor acts as an additional electrode, while the other capacitive sensor(s) are then used to detect objects.

[0035] In a further development of the invention, the exclusive application of the first transmission signal to the first capacitive sensor, the exclusive application of the first transmission signal to the second capacitive sensor, and the simultaneous application of the first transmission signal to at least two capacitive sensors are provided sequentially.

[0036] In this way, the capacitive sensors are operated sequentially: first as a sensor for detecting objects, then as a second electrode, and finally simultaneously as sensors for detecting objects. Higher sensitivity can be expected when at least two capacitive sensors are operated simultaneously for object detection. The different pieces of information obtained can be compared and evaluated, resulting in significantly improved object detection.

[0037] Further features and advantages of the invention will become apparent from the claims and the following description of preferred embodiments of the invention in conjunction with the drawings. Individual features of the different illustrated and described embodiments can be combined with one another in any way without exceeding the scope of the invention. The drawings show: Fig. 1 a schematic representation of a sensor system according to the invention in a first embodiment of the invention, Fig. 2 a schematic representation of the signal waveforms of the sensor system of the Fig. 1, Fig. 3 a sensor system according to the invention in a further embodiment of the invention, Fig. 4 A schematic representation of the field profile in a first operating phase of the sensor system of the Fig. 3, Fig. 5 a schematic representation of the field profile in a second operating phase of the sensor system of the Fig. 3, Fig. 6 a schematic representation of the field profile in a third operating phase of the sensor system of the Fig. 3, Fig. 7 a schematic representation of the field profile in an operating phase of the sensor system of the Fig. 1, Fig. 8 A schematic representation of the field profile during a further operating phase of the sensor system of the Fig. 3, Fig. 9 a schematic representation of two capacitive sensors, Fig. 10 a schematic representation of a sensor system according to a further embodiment of the invention, Fig. 11 a schematic representation of a sensor system according to a further embodiment of the invention, Fig. 12 a qualitative representation of the received signals of the sensor system of the Fig. 11, and Fig. 13 a further qualitative representation of the received signals of the sensor system of the Fig. 11.

[0038] The presentation of Fig. Figure 1 schematically shows a sensor system according to the invention for securing a motor-operated door 10, wherein the sensor system can generally be used for securing moving objects. The door 10 is pushed or folded over an opening 14 in the direction of arrow 12 until it is closed. The door 10 is shown only in section. A capacitive sensor 16 is arranged on a closing edge of the door 10 located at the front in the closing direction 12. The sensor 16 is designed to detect a moving object, for example a human hand, within the opening 14 when the door 10 moves in the closing direction 12. The capacitive sensor 16 is actuated with a transmission signal by a control unit. A section 18a of the control unit is shown schematically and serves to generate the transmission signal.

[0039] A further section 18b of the control unit is also connected to the capacitive sensor 16 and serves to evaluate a received signal output by the capacitive sensor 16. Depending on whether an object, such as a human hand, is present within the field generated by the transmitted signal and emanating from the capacitive sensor 16, the received signal output by the capacitive sensor 16 changes. In this way, the capacitive sensor 16, in conjunction with the control unit 18a, 18b, can detect the presence of an object within the opening 14. The described basic operating principle of capacitive sensors is well known to those skilled in the art.

[0040] According to the invention, a further electrode 20 is arranged at a boundary of the opening 14 opposite the closing edge of the door 10. The receiving electrode 20 has essentially the same dimensions as the capacitive sensor 16 (or can form part of a capacitive sensor) and extends substantially across the entire width of the opening 14. When the capacitive sensor 16 is subjected to a transmit signal, this signal is received by the further electrode 20. The received signal of the further electrode 20 changes depending on the distance between the capacitive sensor 16 and the further electrode 20. The received signal is fed by the further electrode 20 to section 18b of the control unit and evaluated. This evaluation can be performed separately from the evaluation of the received signal from the capacitive sensor 16.By evaluating the received signal from the further electrode 20, information about the distance between the capacitive sensor 16 and the further electrode 20 can be derived; in other words, information about the closed state of the door 10. Distance information can also be obtained if, as provided for in the invention, the further electrode 20 is supplied with a transmitted signal, which is received by the capacitive sensor 16, which is then passively switched and simultaneously does not itself emit a signal at the frequency of the transmitted signal from the further electrode 20, and the received signal at the capacitive sensor 16 is then evaluated with regard to a distance between the further electrode 10 and the capacitive sensor 16.

[0041] Fig. Figure 2 qualitatively shows the course of the first received signal S1 from the capacitive sensor 16 and the second received signal T1 from the further electrode 20. Fig. 2 is the signal S1 qualitatively in volts across the decreasing distance in meters between the capacitive sensor 16 and the further electrode 20, see Fig. Figure 1 shows that the signal amplitude of the first received signal S1 decreases as the distance between the capacitive sensor 16 and the other electrode 20 decreases. In other words, the signal amplitude of the first received signal S1 decreases when the door 10 closes. This decrease in the signal amplitude of the first received signal S1 is caused by its approach to the grounded closing edge of the opening 14.

[0042] In Fig. Figure 1 also shows the qualitative course of the second received signal T1 in volts plotted against the decreasing distance between the capacitive sensor 16 and the other electrode 20. The signal amplitude of the second received signal T1 increases with decreasing distance between the capacitive sensor 16 and the other electrode 20.

[0043] The solid waveform of the received signals S1 and T1 corresponds to the waveform of these two signals when there is no object to be detected in the aperture 14.

[0044] The dashed line representing the two received signals S1 and T1 corresponds to the signal profile when an object to be detected is present in the opening 14. It can be seen that the two received signals S1 and T1 drop sharply downwards simultaneously, using the example of a distance of slightly more than 0.5 m between the capacitive sensor 16 and the other electrode 20.

[0045] After this sudden drop, the first received signal S1 then runs essentially horizontally, before reverting to the course of the first received signal S1 without the presence of an object, in Fig. 2, therefore, to align with the continuous waveform of the first received signal S1. Consequently, the first received signal S1 reacts to the presence of an object, which represents an additional connection to ground, with a distinct signal drop. During normal operation of the sensor system, this signal drop is then used to stop or reverse the motor-driven door 10. If the door 10 continues to move even after an object is detected, as illustrated in the following, Fig. As shown in Figure 2, the signal change caused by the object remains in the received signal 1.

[0046] In the second received signal T1 from the second electrode 20, the presence of an object simultaneously with the first received signal leads to a significant signal drop. Since the object to be detected represents an additional connection to ground, the signal amplitude of the second received signal T1 is reduced. If, despite the presence of an object (which, as explained, does not correspond to normal operation), the door 10 is closed further, the second received signal T1 rises accordingly. Fig. The 2 dashed line resumes, but due to the still present object, the signal level remains lower than in the solid line shown case without an object to be detected.

[0047] It is immediately apparent from the solid and dashed signal waveforms of the second received signal T1 that the distance information derived from the second received signal T1 is distorted when a detectable object is present. However, this is irrelevant for the operation of the sensor system because, as already explained, after an object is detected, the door 10 is stopped or reversed in normal, practical operation due to the sudden drop in the signal of the first received signal S1. Therefore, as soon as an object is detected by the capacitive sensor 16, the distance information derived from the second received signal T1 is no longer relevant, since the door will be stopped or reversed anyway.

[0048] Once the object is removed from the movement path of door 10, the distance information from the second received signal T1 is no longer distorted, as it then follows the continuous path again.

[0049] A differential signal can be calculated from the two received signals S1 and T1. When generating the received signal, the first received signal S1 and / or the second received signal T1 can optionally be weighted. The resulting differential signal is then essentially independent of the closed position of the door 10, in other words, independent of the distance between the capacitive sensor 16 and the other electrode 20. This has the significant advantage that objects in the gap between the opening and the door can still be detected even immediately before the door 10 closes completely, i.e., just before the capacitive sensor 16 makes contact with the receiving electrode 20.

[0050] Fig. Figure 2 shows that this is no longer possible shortly before the door is finally closed using the first received signal S1, since the signal level of the first received signal S1 is already close to zero shortly before the door is finally closed. In contrast, the differential signal, which is essentially independent of the door's closing state, still allows objects within the opening 14 to be detected even shortly before the door 10 is finally closed. The sensor system according to the invention thus enables improved object detection.

[0051] Fig. Figure 3 shows a schematic representation of another sensor system according to the invention for detecting or securing moving objects. The sensor system has several capacitive sensors 16, 22, 24, and 26, the number of which is unlimited, as indicated by three dots between sensors 24 and 26. The capacitive sensors 16, 22, 24, and 26 can be successively stimulated with a transmission signal generated by section 18a of a control unit. Fig. As can be seen from section 3, only one of the sensors 16, 22, 24, 26 can be supplied with the transmission signal from section 18a at any given time. For example, the sensors 16, 22, 24, 26 can be supplied with the transmission signal sequentially using a time-division multiplexing technique.

[0052] A received signal from the capacitive sensors 16, 22, 24, 26 is each amplified and fed to section 18b of the control unit, where an evaluation takes place.

[0053] In the depicted state of the sensor system the Fig. 3 the capacitive sensor 16 is supplied with the transmit signal and the capacitive sensor 16 passes the first received signal S1 to section 18b.

[0054] The second capacitive sensor 22 is in the depicted state of the system in Fig. Sensor 3 is not receiving the transmission signal and is therefore passive. The second capacitive sensor 22 operates in the depicted state. Fig. 3 thus acts as another electrode and forwards the second received signal T1 to section 18b of the control unit. As already shown from the Fig. As explained in section 1, distance information between the two sensors 16 and 22 can be obtained from the second received signal T1.

[0055] The third capacitive sensor 24 is also in the state of Fig. Sensor 3 is not supplied with a transmit signal and is therefore passive. The third capacitive sensor 24 consequently transmits a third receive signal to section 18b, which is designated T2 and which can also be evaluated to obtain distance information about the distance between sensors 16 and 24.

[0056] Similarly, all other sensors, for example sensor 26, are in the state of Fig. 3 passive. Consequently, the other sensors also transmit a received signal to section 18b, and these further received signals can be used to determine a distance between the other sensors and the first capacitive sensor 16. For clarity, the connections between sensor 26 and sections 18a and 18b of the control unit are shown in Fig. 3 not shown.

[0057] In the state of Fig. 3. Using the first received signal S1 from the first capacitive sensor 16, an obstacle in the movement range of a moving object, in particular a door or flap, can thus be detected. The second received signal T1 from the second capacitive sensor 22 serves, in the state of Fig. 3 to obtain information about the distance between the two capacitive sensors 16, 22.

[0058] Similarly, the third received signal T2 from the third capacitive sensor 24 serves in the state of Fig. 3 to obtain information about the distance between the two capacitive sensors 16, 24. The signal from the other capacitive sensors, for example the capacitive sensor 26, is evaluated in the same way.

[0059] Starting from the state of Fig. 3. When the second capacitive sensor 22 is supplied with the transmit signal from section 18a, the received signal of the second capacitive sensor 22 is used to detect an obstacle. The received signal of the first capacitive sensor 16 and the other capacitive sensors 24, 26 is then used to obtain information about the distance between the second capacitive sensor 22 and the first capacitive sensor 16 or the other capacitive sensors 24, 26.

[0060] Based on the state of the Fig. 3. Consequently, in the sensor system, only one of the capacitive sensors 16, 22, 24, 26 is ever activated by the transmit signal from section 18a of the control unit. Only the received signal from this single capacitive sensor is then used to detect obstacles. The received signals from the other capacitive sensors are also evaluated, but serve only to obtain information about the distance between the capacitive sensor currently being activated by a transmit signal and the other capacitive sensors.

[0061] The presentation of Fig. Figure 4 shows a schematic representation of the electric field that exists in the state of Fig. 3 is generated. As explained, only the first capacitive sensor 16 is supplied with a transmit signal. The other capacitive sensors 22, 24, on the other hand, are passively connected and do not generate an electric field themselves. Based on the representation of the field lines emanating from the capacitive sensor 16, it is also easy to see that the received signal at the capacitive sensors 22, 24 becomes stronger the smaller the distance between the first capacitive sensor 16 and the second or third capacitive sensor 22, 24.

[0062] Fig. Figure 5 schematically illustrates the course of the electric field when the second capacitive sensor 22 is energized with the transmission signal. The first capacitive sensor 16 and the third capacitive sensor 24 are passively switched in this state and do not themselves generate an electric field.

[0063] Fig. Figure 6 shows the state in which only the third capacitive sensor 24 is energized with the transmission signal. The other two capacitive sensors 16 and 22 are passively switched in this case and consequently do not generate an electric field themselves.

[0064] The presentation of Fig. Figure 7 schematically shows a sensor system that is essentially the same as the sensor system of the Fig. This corresponds to 1. The first capacitive sensor 16 and the second electrode 20 are provided. The second electrode 20 is intermittently supplied with a transmission signal, thereby generating an electric field, whereas the first capacitive sensor 16 is passively switched off when the second electrode 20 is supplied with a transmission signal. The signal emitted by the second electrode 20 can therefore be received by the capacitive sensor 16 to obtain information about the distance between the second electrode 20 and the first capacitive sensor 16.

[0065] Fig. Figure 7 thus schematically represents an alternative operating mode in which, at times or with a different frequency or modulation, the additional electrode 20 acts as the transmitting electrode and the capacitive sensor 16 as the additional electrode. Based on the Fig. The operating method described in point 7 can, for example, be used alternately with the one based on the Fig. The operating procedure described in point 1 must be carried out to check the function of the sensor system.

[0066] Fig. Figure 8 schematically represents a sensor system with three capacitive sensors 16, 22, 24. In contrast to the sensor system of Fig. However, capacitive sensors 16 and 22 are simultaneously supplied with a transmit signal. Only the third capacitive sensor 24 is passively switched. If both capacitive sensors 16 and 22 are supplied with a transmit signal simultaneously, more sensitive obstacle detection can be expected if the two capacitive sensors 16 and 22 are very close to each other. To facilitate or even enable the evaluation of the received signals from the two capacitive sensors 16 and 22, these received signals are compensated by the received signal from the passively switched capacitive sensor 24. The received signals of the two capacitive sensors 16 and 22, which are supplied with a transmit signal, are then essentially independent of the distance between the two sensors 16, 22 and detection of obstacles is possible even with a very small distance between the two sensors 16, 22.

[0067] Of course, only one of the capacitive sensors 16, 22, 24 can be successively supplied with a transmission signal, and then two of the sensors 16, 22, 24 at a time, in order to enable even further improved detection of obstacles and greater operational reliability.

[0068] Fig. Figure 9 schematically shows two capacitive sensors 16, 22, which are movable relative to each other and in which, as shown by the Fig. As explained in section 3, the capacitive sensors 16 and 22 are alternately activated with a transmission signal or switched to passive mode to obtain distance information. This alternating operation results in redundant signals and therefore increased reliability of the sensor system. Functional testing of both capacitive sensors 16 and 22, as well as the associated control unit, is also possible.

[0069] As an alternative to the operating methods already discussed, several capacitive sensors 16, 22, 24, 26 can also be used, with each of the capacitive sensors 16, 22, 24, 26 being simultaneously supplied with a transmission signal at a different frequency. Each of the capacitive sensors 16, 22, 24, 26 must then be assigned a control unit that can simultaneously evaluate received signals on all frequencies used as transmission signals. This allows each of the capacitive sensors 16, 22, 24, 26 to simultaneously detect obstacles and obtain distance information from each sensor to the other sensors.

[0070] This type of operation also allows for the permanent monitoring of the functionality of the sensor system.

[0071] Fig. Figure 10 shows a sensor system according to a further embodiment of the invention. Capacitive sensors 16, 22, 24, 26, and 28 are provided. Each of the capacitive sensors 26 to 28 is assigned a separate control unit 30, 32, 34, 36, 38. The control units 30, 32, 34, 36, 38 transmit a signal to each of the capacitive sensors 16, 22, 24, 26, 28 and also evaluate the respective received signal of the capacitive sensors 16, 22, 24, 26, 28. The control units 30 to 38 are also designed to temporarily switch the capacitive sensors 16 to 28 to passive mode, i.e., not to apply a transmission signal, and then to obtain the respective distance signal to obtain information about the distance between the capacitive sensors 16 to 28.

[0072] Alternatively, the control units 30 to 38 are suitable for generating transmitted signals of different frequencies and evaluating received signals of different frequencies, as explained above. Assigning one control unit 30 to 38 to each of the capacitive sensors 16 to 28 also facilitates the spatially separated installation of capacitive sensors, for example, when securing very large doors or flaps. It is essential, however, that the control units 30 to 38 are synchronized with each other. This can be achieved by a Fig. Synchronization can be performed via the synchronization lines 40 (shown with dashed lines), or alternatively wirelessly via a radio signal.

[0073] According to a further embodiment of the invention, synchronization of the control units 30 to 38 can be dispensed with, and consequently, the Fig. The synchronization line 40, shown as a dashed line, is omitted if each control unit 30 to 38 knows the frequencies of the other control units. For example, all control units 30 to 38 operate at different frequencies when generating a transmitter signal for their respective assigned sensor and when evaluating the received signal from that sensor. Control unit 30 then knows the frequencies at which control units 32 to 38 operate; control unit 32 knows the frequencies at which control units 30, 34, 36, and 38 operate; control unit 34 knows the frequencies at which control units 30, 32, 36, and 38 operate; control unit 36 ​​knows the frequencies at which control units 30, 32, 34, and 38 operate; and control unit 38 knows the frequencies at which control units 30 to 36 operate.By filtering the signal in control units 30 to 38, the signal from each adjacent sensor can then be received and evaluated. Based on this signal, information about the distance between sensors 16 to 28 is then available. The signal from the control unit's own sensor can then be compensated for with this signal. For example, control unit 30 evaluates the signal from sensors 22 to 28 and uses this signal to compensate for the signal of its assigned sensor 16.

[0074] Fig. Figure 11 schematically shows the sensor system of the Fig. 9 with the two capacitive sensors 16 and 22. The two sensors 16 and 22 are movable relative to each other. In contrast to the one based on the Fig. In the operating mode described in section 9, only the capacitive sensor 22, which is located in the Fig. As shown on the right in Figure 11, a transmission signal is emitted, which is indicated by the arrows 40.

[0075] Fig. Figure 12 qualitatively shows the signal profile of the received signals at the two capacitive sensors 16, 22 when the two capacitive sensors 16, 22 are moved towards each other. Fig. Figure 12 shows the signal waveform without the presence of an object.

[0076] Fig. Figure 13 also shows the signal profile of the received signals at the two capacitive sensors 16, 22, whereby in the case of the Fig. 13 an object is located between the two capacitive sensors 16, 22.

[0077] In Fig. Figure 12 shows curve 42, which depicts the signal waveform at the capacitive sensor 22, from which the transmit signal 40 originates. It is in Fig. 12. It is clearly visible that the signal strength of the received signal at the capacitive sensor 22 decreases as the distance between the two capacitive sensors 16, 22 decreases. This is caused by the approach of the capacitive sensor 22 to grounded sections of a closing opening and / or a mounting of the first capacitive sensor 16.

[0078] The received signal 44, measured at the capacitive sensor 16, increases as the distance between the two sensors decreases. The closer the two capacitive sensors 16, 22 get, the greater the influence of the transmitted signal 40 on the received signal at the capacitive sensor 16.

[0079] At time t1, the distance between the two capacitive sensors 16, 22 is approximately zero.

[0080] Fig. Figure 13 shows the two signals 42 and 44, which were already identified based on the Fig. 12 explained, in the presence of an object between the two capacitive sensors 16, 22.

[0081] At time t0, an object, for example a human hand, enters the space between the two capacitive sensors 16, 22. This causes a signal drop 46 in the received signal 42 of the capacitive sensor 22, which is Fig. 13 is circled with a dashed line. This sudden drop in signal is typically used to detect the object and then causes the movement of the two capacitive sensors 16, 22 towards each other to stop or reverse. For clarity, the signal waveform of the Fig. 13 The two capacitive sensors 16, 22 continued to move towards each other despite the presence of the object. It can be seen that the signal change caused by the object at 46, i.e. an offset towards zero, is maintained as the two capacitive sensors 16, 22 continue to approach each other and thus as signal 42 continues to move.

[0082] The influence of the object on the received signal 44 at the capacitive sensor 16 is less than the influence on the received signal 42 at the capacitive sensor 22. However, compared to the course of the Fig. 12 a signal drop, which then persists throughout the further course of the approach.

Claims

[1] Sensor system for securing moving objects, in particular motor-operated doors (10) or flaps, comprising at least one capacitive sensor (16), wherein the capacitive sensor has at least one first electrode, and comprising at least one control unit (18a, 18b), wherein the control unit (18a, 18b) is configured to generate a first transmit signal for the at least one capacitive sensor (16) and to evaluate a first received signal (S1) from the at least one capacitive sensor (16), characterized byat least one further separate second electrode (20) spatially separated from the sensor (16), wherein the at least one capacitive sensor (16) and the at least one further second electrode (20) are movable relative to each other, and wherein means for generating a second transmit signal for the at least one further second electrode, wherein the first transmit signal and the second transmit signal are either different or time-shifted from each other, and / or means for evaluating a second receive signal (T1) from the at least one further second electrode (20) are provided, wherein the first receive signal (S1) and the second receive signal (T1) are different. [2] Sensor system according to claim 1, characterized by, that the at least one control unit (18a, 18b) has means for evaluating the second received signal (T1) from the at least one further second electrode (20), and wherein the means for evaluation are configured to derive information about the distance between the at least one capacitive sensor (16) and the further second electrode (20) from the second received signal (T1). [3] Sensor system according to claim 1 or 2, characterized by , that the control unit has means for evaluating the second received signal (T1) from the at least one further second electrode (20) and is designed to calculate a differential signal, wherein the differential signal is formed from the, optionally weighted, first received signal (S1) of the at least one capacitive sensor (16) and the, optionally weighted, second received signal (T1) of the at least one further second electrode (20). [4] Sensor system according to one of the preceding claims, characterized by , that at least one further second electrode (20) forms part of a second further capacitive sensor (22, 24, 26). [5] Sensor system according to claim 4, characterized by , that at least two capacitive sensors are provided, wherein the control unit is designed to apply a transmission signal to the capacitive sensors successively. [6] Sensor system according to claim 4, characterized by , that at least two capacitive sensors (16, 22, 24, 26) are provided, wherein the control unit (18a, 18b) is configured to generate a transmit signal with a different frequency for each capacitive sensor (16, 22, 24, 26). [7] Sensor system according to one of the preceding claims, characterized by, that the control unit (18a, 18b) has a memory and means for comparison, wherein at least one signal waveform of the second received signal (T1) of the further second electrode and an associated distance between the capacitive sensor (16) and the further second electrode (20) is stored in the memory and wherein means for comparing the second received received signal (T1) with the stored second received signal (T1) are provided in order to obtain information about the distance between the capacitive sensor (16) and the further second electrode (20). [8] Sensor system according to claim 7, characterized by , that the control unit has means for learning and storing a signal profile of the second received signal (T1) and the associated distance between the capacitive sensor (16) and the further second electrode (20). [9] Sensor system according to any one of the preceding claims, characterized by, that the control unit has spatially distributed sub-control units (30, 32, 34, 36, 38), wherein each capacitive sensor (16, 22, 24, 26, 28) and / or each further second electrode is assigned a sub-control unit (30, 32, 34, 36, 38) and wherein the sub-control units (30, 32, 34, 36, 38) are each configured to generate a transmit signal and wherein the sub-control units (30, 32, 34, 36, 38) are synchronized at least with respect to generating the transmit signals. [10] Sensor system according to claim 9, characterized by , that the sub-control units (30, 32, 34, 36, 38) are each equipped with a serial interface for communication with the other sub-control units (30, 32, 34, 36, 38). [11] Method for operating a sensor system for securing moving objects, in particular motor-operated doors or flaps, with at least one capacitive sensor, wherein the capacitive sensor has at least one first electrode, with at least one control unit, wherein the control unit is configured to generate a first transmit signal for the at least one capacitive sensor and to evaluate a first received signal from the at least one capacitive sensor, with at least one further separate second electrode spatially separated from the sensor, wherein the at least one capacitive sensor and the at least one further second electrode are movable relative to each other, comprising the steps of evaluating a second received signal from the at least one further second electrode and / or generating a second transmit signal for the at least one further second electrode,where the first transmitted signal and the second transmitted signal are either different or time-shifted from each other, and where the first received signal and the second received signal are different. [12] Method according to claim 11, characterized by Deriving information about the distance between the at least one capacitive sensor and the second electrode from the second received signal. [13] Method according to claim 11 or 12, characterized by Forming a difference signal from the first and second received signals. [14] Method according to claim 11, 12 or 13, characterized by Comparing the second received signal of the second electrode with a stored profile of the second received signal, wherein the stored profile is assigned a profile of the distance between the capacitive sensor and the second electrode. [15] Method according to claim 14, characterized bySaving a history of the second received signal and the associated distance by means of learning. [16] Method according to any one of claims 11 to 15, wherein the sensor system comprises at least two capacitive sensors, characterized by Applying the first transmission signal to the two capacitive sensors one after the other in a sequential manner. [17] Method according to claim 16, characterized by , successively, applying the first transmission signal exclusively to the first capacitive sensor, applying the first transmission signal exclusively to the second capacitive sensor, and simultaneously applying the first transmission signal to at least two capacitive sensors.

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