Method for detecting ballistocardiogenic and / or respiratory movements of a person sitting on a motor vehicle seat and measuring arrangement for carrying out the method

Abstract

Method for detecting ballistocardiogenic and / or breathing-related movements of a person (20) located on a vehicle seat (10) of a motor vehicle, in which a first sensor (21) is designed as a ballistographic sensor for detecting the ballistocardiogenic and / or breathing-related movements of the person (20) and delivers a ballistographic signal and a second sensor (22) generates a vibration signal as an interference reference for the ballistographic signal, characterized in that - a ballistographic sensor is used as the second sensor (22), - the second sensor (22) is arranged in the motor vehicle seat (10) in a vibration-insulated manner relative to the person (20), and - an algorithm is used to minimize interference of the ballistographic signal by means of the vibration signal.

Description

The invention relates to a method for detecting ballisticocardiogenic and / or breathing-related movements of a person located on a vehicle seat of a motor vehicle according to the preamble of claim 1 and to a measuring arrangement for carrying out the method according to the invention.The contactless monitoring of the heart activity of a person is carried out by detecting the minimum movements of this person, which are attributable to the heart beat, i.e. the heart recoil movements, so-called ballistic heart movements by means of ballistically acting sensors. Also, the breathing of a person generates a movement in his body, which movement can likewise be detected with ballistographic sensors.A generic method is known from WO 2010 / 045455 A1, which generates a ballistocardiogram for monitoring the heart function of a person by means of a ballistographic sensor, wherein physiological features of the person and noise or interference signals in the environment of the first sensor are detected by means of a second sensor. The signals of the two sensors are fed to a processor unit which generates from this a ballisticographic signal reduced in interference signal which indicates the heart condition of the person. The first sensor is arranged in a vehicle seat of a motor vehicle and generates a ballisticographic signal on account of the ballisticocardiogenic movement of a person sitting on the vehicle seat, while the second sensor is located on the floor of the motor vehicle and serves as a noise signal reference for the ballisticographic signal. The second sensor is designed as a seismic sensor (hydrophone) or as an acceleration sensor.Furthermore, WO 2008 / 102298 A1 describes a ballistographic measurement system which comprises at least one ballistographic sensor for detecting ballistocardiogenic movements of the body of a person and a further sensor for measuring interference signals, wherein this further sensor is vibration-isolated from the body of the person and is designed as a seismic sensor which is arranged on the floor or on a bed of the person. The faulted ballisticographic signal is processed by means of the signal of the vibration-isolated sensor in order to generate a ballistographic signal reduced in interference signal or free of interference signal.The disadvantage of these known methods according to WO 2010 / 045455 A1 and WO 2008 / 102298 A1 is that different sensor types are used for the first and second sensor. The use of different sensor types leads, on the basis of the principle, to the generation of different measurement signals, even with the same excitation by the interference signals, as a result of which the elimination of the interference signals from the ballisticographic signal by means of suitable calculation methods is made more difficult, i.e. the evaluation requires the provision of a high calculation capacity and thus leads to high costs.DE 10 2004 016 191 A1 discloses a restraint system having a restraint belt. In this case, a motion sensor (preferably an acceleration sensor) is mechanically installed in the restraint belt in such a way that it can record the movements of the rib cage in the best possible manner.U.S. Pat. No. 6,337,629 B1 shows a method for warning a person of a falling back in a vehicle. Wakefulness is determined by means of a first physiological parameter (of the vegetative nervous system, such as breathing movements) with the aid of a sensor as soon as this parameter follows a certain pattern which indicates tiredness, a second parameter is used. This second parameter validates whether the driver's operating interventions (steering, braking, accelerating) still take place to an extent that indicates an awake person. If a limit value is also reached in this case, an alarm is triggered which is intended to wake up the person.WO 2010 / 045455 A1 discloses a system which records a ballistocardiogram [BCG] for a user on a scale. In this case, a BCG signal is recorded by a first sensor in a body balance and a noise signal of the environment is detected by a second sensor on the ground. A noise suppression circuit generates a corrected BCG signal, which indicates the state of the heart of the user.U.S. Pat. No. 7,417,536 B2 describes a method for detecting living beings, in particular a human, by detecting the pressure wave generated by the heart beat or the breathing of the human in the body thereof by means of a pressure transducer. To generate such ballistic signals, strain gauges, load cells, acceleration sensors, hydrophones, laser viscometers, fiber-optic sensors or microwave radiometers are proposed as sensors for these pressure sensors. Since the sensor signals contain the ballisticographic signals with only low signal strength and low signal-to-noise ratio, a complex mathematical algorithm is used for the evaluation. With this algorithm, the signals from different types of sensors are processed in order to be able to carry out seat occupancy detection for a motor vehicle, for example.As a measuring arrangement for such seat occupancy detection, two sensors are arranged in the seat frame of a vehicle seat, which sensors detect the pressure acting on the vehicle seat. Furthermore, two further sensors are provided in the interior of the vehicle and also one further sensor outside the interior of the vehicle. The signals from these sensors are fed for processing to a processor which uses data from a memory for this purpose. For example, for detecting seat occupancy, this memory contains first data indicating an occupied seat and second data indicating an unoccupied seat. Data can also be stored in such a memory, with which a specific characteristic state of a person on the vehicle seat can be established, such as, for example, the awake state thereof.This known method and the associated measuring arrangement also require, in a cost-disadvantageous manner, more than two sensors of different types and a complicated mathematical algorithm for which a high computing capacity must be made available. Furthermore, a sufficient database is also to be provided in order to achieve a high level of recognition reliability which is required for vehicle applications and which in turn leads to a high storage space requirement and thus also entails high costs.From the article "The Potential of EMFi Sensors in Heart Activity Monitoring", Jarmo Alametisa J., Farri V., Koivuluoma M., Barna L., 2nd OpenECG Workshop "Integration of the ECG into the EHR & Interoperability of ECG Device Systems", 1-3. April, 2004, Berlin, Germany, discloses an investigation with regard to the use of electromechanical film sensors as ballistographic sensors. According to EP 0 182 764 B1, these sensors consist as dielectric element of a flexible and thin plastic film made of biaxially oriented polypropylene, which converts mechanical energy into an electrical signal and, conversely, electrical signals into mechanical energy. This plastic film is coated with a permanently polarized electrically conductive layer. When the pressure on this plastic film changes, electrical charges are generated on the conductive surface, which can be measured as current or voltage. The sensitivity of such film sensors is substantially greater than that of conventional piezoelectric sensors. In the article mentioned, reference is made to the low stability with respect to sensitivity at temperatures above 50° C. Thus, in use, the ambient temperature should be maintained constant at 50°C. However, this restricts use in vehicle construction, since such temperatures in a motor vehicle cannot be excluded.It is an object of the invention to provide a method for detecting ballistocardiogenic and / or breathing-related movements of a person of the type mentioned at the beginning who is located on a motor vehicle seat, with which method a ballistographic signal can be generated with minimized interference signals and a high signal-to-noise ratio, which can be carried out simply and thus economically. It is a further object of the invention to specify a measurement arrangement for a vehicle seat of a motor vehicle for carrying out the method according to the invention, which measurement arrangement can be realized in a simple and thus cost-effective manner.The first-mentioned object is achieved by a method having the features of claim 1.Such a method for detecting ballistocardiogenous and / or breathing-related movements of a person located on a vehicle seat of a motor vehicle, in which a first sensor is designed as a ballistocardiogenous sensor for detecting the ballistocardiogenous and / or breathing-related movements of the person and supplies a ballistographic signal and a second sensor generates an oscillation signal as a disturbance reference for the ballistographic signal, is characterized according to the invention in thata ballistically configured sensor is used as the second sensor,the second sensor is arranged in the motor vehicle seat in a vibration-isolated manner with respect to the person, andan algorithm for minimizing interference signals of the ballisticographic signal by means of the oscillation signal is used.This method according to the invention uses the realization that with the use of two ballistic sensors arranged in the vehicle seat, preferably pressure sensors, sensor signals are generated both for the detection of the ballistic movements and for the detection of the vehicle oscillations, which sensor signals have a substantially identical interference signal structure, whereby only a small outlay is required with regard to an algorithm evaluating the signals and thus only a small amount of computing capacity is required. Furthermore, due to the almost identical interference signal structure of the two sensor signals, a high signal-to-noise ratio of the processed ballisticographic signal of the first sensor is achieved.A method that can be implemented particularly easily results if, according to one embodiment of the invention, the first and second sensor are each designed with a directionality with respect to the measured variables to be detected. Such sensors having a directional characteristic with respect to the pressure to be detected are arranged in the vehicle seat in such a way that the first sensor is pressure-sensitive only in the direction of a person located on the vehicle seat and the second sensor is pressure-sensitive only in the direction of the vehicle floor for measuring the vehicle vibrations, that is to say the disturbing noises.Furthermore, the noise-signal ratio of the ballisticographic signal processed with the algorithm using the signal of the second sensor is further improved if, according to one embodiment of the invention, the first and second sensors operate according to the same measurement principles. This is because the signals of these two sensors have an almost identical interference signal structure.The second object mentioned is achieved by a measuring arrangement for a vehicle seat of a motor vehicle having the features of patent claim 5.This measuring arrangement according to the invention for a vehicle seat of a motor vehicle having a first sensor which is designed as a ballistocardiogenic sensor and / or respiration-related movements of a person located on the vehicle seat and a second sensor is provided for detecting oscillations of the motor vehicle is distinguished according to the invention in thatthe second sensor is designed as a ballistrographic sensor,the first and second sensor are arranged in the region of a seat cushion of the vehicle seat, andthe second sensor is arranged in a vibration-isolated manner with respect to the person.Since both sensors, which are each preferably designed as pressure sensors, are installed in the vehicle seat, it is possible to reduce installation costs compared with the prior art in which the second sensor is mounted outside the motor vehicle seat, since both sensors can be mounted simultaneously, only one cable harness has to be led to the vehicle seat and also only one plug connection is required.In one embodiment of the invention, it is provided that the first and second sensor are each designed with a directionality with respect to the measured variables to be detected; the first sensor is arranged in the region of the seat cushion in such a way that the ballistocardiogenic and / or breathing-related movements of the person are detected, and the second sensor is arranged in the region of the seat cushion in such a way that only the oscillations of the motor vehicle are detected, but not the ballistographic movements of the person.By using such direction-sensitive pressure sensors, it is no longer necessary to equip the vehicle seat with special vibration-isolating means.According to a further development of the invention, it is particularly advantageous if the first and second sensors operate according to the same measurement principles, whereby the noise-signal ratio of the ballisticographic signal processed with the algorithm using the signal of the second sensor is further improved, since the signals of the two sensors have an almost identical interference signal structure.In a further embodiment of the invention, the vehicle seat has a vibration-isolating means for vibration isolation of the second sensor from the person, which means is preferably designed as a damping mat. Thus, the ballistic movements of a person sitting on the vehicle seat can be isolated from the second sensor in a targeted manner.A cost-effective development of the invention results when the second sensor is arranged in the edge region or in a corner region of the seat cushion of the vehicle seat. Thus, a position for this sensor which is largely vibration-isolated is already achieved by such an arrangement of the second sensor in the vehicle seat, since the ballistic movements are largely no longer detectable in the edge region of the seat cushion, since the sensitivity of the second sensor is not sufficient for this purpose.Finally, according to a last advantageous development of the invention, it is provided that, for evaluating the sensor signals of the first and second sensor, an evaluation unit is provided which generates a ballisticographic signal with minimized interference signals by means of the sensor signal of the second sensor, wherein a control unit of a matching assistance system of the vehicle can also be used for this purpose.The measuring arrangement according to the invention can advantageously be used for monitoring the heartbeat and / or the heartbeat frequency and / or the breathing and / or the breathing frequency, wherein a corresponding control device is provided for this purpose, which automatically carries out an emergency stop when a life-threatening heart condition or a lack of breathing by the vehicle driver is detected and additionally sends an emergency signal to an external emergency station.Furthermore, it is possible to use the measuring arrangement according to the invention for detecting fatigue of a vehicle driver by evaluating the processed ballisticographic signal with minimized interference signals with regard to the fatigue state of the driver.Finally, a seat occupancy detection can also be realized with the measuring arrangement according to the invention, since the detection of a heartbeat movement or a breathing movement indicates the occupancy of the vehicle seat with a person.The invention is described in detail below on the basis of exemplary embodiments with reference to the appended figures. The following are shown: FIG. 1 shows a schematic illustration of a measuring arrangement in a vehicle seat of a motor vehicle for carrying out the method according to the invention as an exemplary embodiment, FIG. 2 shows a schematic illustration of a vehicle seat according to FIG. 1 with an alternative measuring arrangement, and FIG. 3 shows a schematic illustration of a vehicle seat according to FIG. 1 with a further alternative measuring arrangement.FIGS. 1 to 3 show a schematically illustrated vehicle cabin 1 of a motor vehicle having a vehicle seat 10 which is occupied by a person 20.This vehicle seat 10, which consists of a seat cushion 11 and a seat back 12, is mounted on a base 13, for example on seat side members. The seat cushion 11 comprises a first sensor 21 and a second sensor 22 in different measuring arrangements according to FIGS. 1 to 3, wherein both sensors 21 and 22 are designed as ballistic pressure sensors.According to FIG. 1, the sensor signals of these two sensors 21 and 22 are fed to a function block 30, which in turn is connected to further function blocks 31 to 34 and whose functions are explained further below.Also, the sensors 21 and 22 of the vehicle seats 10 illustrated in FIGS. 2 and 3 are connected to such function blocks 30 to 34, but are not illustrated in these FIGS. 2 and 3 for simplicity.According to FIG. 1, the first sensor 21 is arranged in the region of the seat cushion 11 of the vehicle seat 10 adjacent to the seat surface, so that the ballistocardiogenic and breathing-related movements of the person 20 are detected by generating corresponding ballistographic signals. This ballisticographic signal also contains the disturbing signals caused by oscillations of the vehicle. On the side of the seat cushion 11 facing away from the seating surface, the second sensor 22 is arranged, which is vibration-isolated from the first sensor 21 by a mechanical damping mat 23, so that this second sensor 22 can substantially only detect the vibrations originating from the vehicle and thus represents a disturbance reference signal for the ballistic signal of the first sensor 21.According to FIG. 1, both sensors 21 and 22 are designed as sensor pressure mats and therefore extend almost over the entire seat surface of the seat cushion 11.The sensor signals of the two sensors 21 and 22 are fed according to FIG. 1 to an evaluation unit 30 for signal processing in order to eliminate as far as possible the interference signals detected by the second sensor 22 from the ballistic signal of the first sensor 21 and to obtain a large signal-to-noise ratio. In the simplest case, the signals of both sensors 21 and 22 are subtracted from one another in the time domain or in the frequency domain, so that the interference signals in the ballisticographic signal are thereby cancelled out. This is extremely effective because, on the one hand, both sensors are mounted in principle at the same location, i.e. in the seat cushion 11 of the vehicle seat 10, and are therefore exposed to identical oscillations or interference signals, and, on the other hand, two pressure sensors, in particular sensors 21 and 22 operating on the same measuring principle, are used, and therefore their interference signal structures are largely identical. In addition to the method of subtracting the sensor signals for the purpose of signal processing, other mathematical methods or algorithms known to the person skilled in the art can also be used.As ballisticographic sensors 21 and 22, it is also possible according to FIG. 1 to use directional sensors, i.e. sensors with a directional characteristic with respect to the measured variables to be detected. Thus, the first sensor 21 is mounted in the seat cushion 11 in such a way that it is pressure-sensitive only "upward", i.e. in the direction of the person 20, while the second sensor 22 is arranged in such a way that it is pressure-sensitive only "downward", i.e. in the direction of the vehicle floor. As a result, a damping mat 23 can be dispensed with.As shown in FIG. 1, the two sensors 21 and 22 are disposed inside the seat cushion 11. In contrast, a measuring arrangement of these sensors 21 and 22 according to FIG. 2 can also be mounted between the base 13 of the vehicle seat 10 and the vehicle seat 10, i.e. below the seat cushion 11. In such a measuring arrangement, it is sufficient to use sensors 21 and 22 with only a small surface area in comparison to the seat surface of the seat cushion 11. In this measuring arrangement, too, the two sensors 21 and 22 are separated by a mechanical damping layer 23, wherein the first sensor 21 is arranged on the seat side and the second sensor 22 is arranged on the base side.A further measuring arrangement with two sensors 21 and 22 in the seat cushion 11 of a vehicle seat 10 is shown in FIG. 3, in which the first sensor 21 is arranged as a sensor mat substantially in a central region of the seat surface of the seat cushion 11, while the second sensor 22 is located in the region of the front edge of the seat cushion 11, since no or only slight ballisticographic movements of the person 20 can be detected there. Thus, this second sensor 22 likewise substantially only detects interference signals or the oscillations of the vehicle. This second sensor 22 can extend over the entire width of the seat cushion 11 or can be arranged only in a corner region of the seat cushion 11. The lateral edge regions of the seat cushion 11 are also suitable for receiving such a second sensor 22.The sensor signals of the sensors 21 and 22 of the measuring arrangements shown in FIGS. 2 and 3 are likewise fed, in accordance with FIG. 1, to an evaluation device 30 for signal processing in order to generate a ballisticographic signal minimized with respect to interference signals.Thus, according to FIG. 1, such a ballisticographic signal can be supplied to a control device 31 for an emergency stop assistant in order to have a safe automatic emergency stop maneuver of the vehicle carried out in the event of a detection of an erroneous heart or breathing activity or a missing heart beat or missing breathing of the person 20 sitting on the vehicle seat 10, which possibly means an inability of the vehicle driver 20 to drive. At the same time, in such an emergency, a corresponding emergency call can be transmitted to a rescue control center via a transmitting device 33, wherein position data of the vehicle can additionally also be transmitted.Furthermore, this interference signal-minimized ballisticographic signal can be used for detecting seat occupancy for pilot control of an airbag control device 32, since a detected cardiac or respiratory activity indicates a vehicle seat occupied by a person.Finally, the interference signal-minimized ballisticographic signal can be used for fatigue detection, so that an optical and / or acoustic warning signal is generated via a display 34 when fatigue of the vehicle driver 20 is detected.Suitable ballisticographic pressure sensors are capacitive sensors in addition to piezoresistive and piezoelectric sensors.Reference numerals denote reference numerals1 Vehicle cabin 10 Vehicle seat 11 Seat cushion of the vehicle seat 10 12 Vehicle backrest of the vehicle seat 10 13 Base of the vehicle seat 10 20 Person 21 First sensor 22 Second sensor 30 Evaluation unit 31 Control device for assistance function for emergency stop 32 Airbag control device 33 Emergency call transmission unit 34 Display

Claims

Method for detecting ballistocardiogenous and / or breathing-related movements of a person (20) located on a vehicle seat (10) of a motor vehicle, in which a first sensor (21) is designed as a ballistocardiogenous and / or breathing-related movements of the person (20) and supplies a ballistographic signal and a second sensor (22) generates a vibration signal as a disturbance reference for the ballistographic signal, characterized in that - a ballistographically designed sensor is used as a second sensor (22), - the second sensor (22) is arranged in the motor vehicle seat (10) in a vibration-isolated manner with respect to the person (20), and - an algorithm for minimizing disturbance signals of the ballistographic signal by means of the vibration signal is used.Method according to Claim 1, characterized in that the first and second sensor (21, 22) are each designed as a pressure sensor.Method according to Claim 1 or 2, characterized in that the first and second sensor (21, 22) are each designed with a directional dependence with respect to the measurement variables to be detected.Method according to one of the preceding claims, characterized in that the first and second sensors (21, 22) operate according to the same measurement principles.Measuring arrangement for a vehicle seat (10) of a motor vehicle having a first sensor (21) which is designed as a ballistocardiac, genetic and / or breathing-related movements of a person (20) located on the vehicle seat (10) and a second sensor (22) is provided for detecting oscillations of the motor vehicle, characterized in that - the second sensor (22) is designed as a ballistocardiac sensor, - the first and second sensor (21, 22) is arranged in the region of a seat cushion (11) of the vehicle seat (10), and - the second sensor (22) is arranged in an oscillation-isolated manner with respect to the person (20).Measuring arrangement according to Claim 5, characterized in that the first and second sensor (21, 22) are each designed as a pressure sensor.Measuring arrangement according to Claim 5 or 6, characterized in that the first and second sensor (21, 22) are each designed with a directional dependence with respect to the measured variables to be detected, - the first sensor (21) is arranged in the region of the seat cushion (11) in such a way that the ballistic-cardiogenic and / or breathing-dependent movements of the person (20) are detected, and - the second sensor (22) is arranged in the region of the seat cushion (11) in such a way that the oscillations of the motor vehicle are detected.Measuring arrangement according to one of Claims 5 to 7, characterized in that the first and second sensors (21, 22) operate according to the same measurement principles.Measuring arrangement according to one of Claims 5 to 8, characterized in that a vibration-isolating means (23) is provided for vibration isolation of the second sensor (22) with respect to the person (20).Measuring arrangement according to Claim 9, characterized in that a damping mat (23) is provided as vibration-insulating means.Measuring arrangement according to Claims 5 to 8, characterized in that the second sensor (22) is arranged in the edge region or in a corner region of the seat cushion (11) of the vehicle seat (10).Measuring arrangement according to one of Claims 5 to 11, characterized in that an evaluation unit (30) is provided for generating a ballisticographic signal with minimized interference signals by means of the sensor signal of the second sensor (22).Use of the measuring arrangement according to one of the preceding claims 5 to 12 for monitoring the heartbeat and / or the heartbeat frequency and / or the breathing and / or the breathing frequency.Use of the measuring arrangement according to one of the preceding claims 5 to 12 for fatigue detection.Use of the measuring arrangement according to one of the preceding claims 5 to 12 for detecting seat occupancy.

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