KR20130032325A - Capacitive sensor system - Google Patents

Abstract

A capacitive sensor system for a vehicle is provided, the system comprising a chassis earth, a signal generator, a signal detector, and a processing unit, the signal generator being applied between the chassis earth and the virtual external earth (with frequency and amplitude) ) Generate a sensor signal. The system includes an earth antenna configured to act as a virtual external earth, the earth antenna being electrically connected to the signal generator and having a predetermined size, and electrically isolated from the chassis earth, as well as a predetermined distance from the ground surface. Disposed on the vehicle. The signal detector is configured to detect and determine the magnitude of the potential between the chassis earth and the external virtual earth and generate and transmit a measurement signal to the processing unit based on the detection and determination, the processing unit processing the measurement signal and processing the processed measurement signal. Is sent to the alarm system, the alarm system is configured to generate one or more alarm signals based on the processed measurement signal.

Description

Capacitive Sensor System {CAPACITIVE SENSOR SYSTEM}

The present invention relates to a capacitive sensor system as described at the end of the independent claim.

Intrusion into, and theft from, trucks, trailers, and semitrailers are currently very important because they are relatively unprotected in the presence of expensive goods being transported along the road. It is a problem. These thefts and intrusions incur significant costs to freight forwarders and insurance companies. This also creates anxiety for drivers when sleeping in trucks. Although locking systems and alarm systems are commonly used to protect vehicles from intrusion and theft, today's systems have several limitations, which makes it difficult to achieve satisfactory protection.

Current solutions for shell protection of trucks are generally based on monitoring of the doors and hatches of the vehicle by an alarm system. In some cases, cargo space doors are also covered by this monitoring, and the shell protection solution detects intrusions when either the door or hatch of the vehicle is opened. do. This is a common solution currently offered by SCANIA and other truck manufacturers.

A disadvantage that can be found in the many shell protections available for trucks is that they are often not suitable for monitoring trailers or semitrailers, or expensive modifications are required to make this possible. Moreover, such systems are often not suited for use on a bus. A good solution for the monitoring of trailers and semitrailers currently does not exist because the tractor units often change trailers and semitrailers. The problem is that both the trailer and semitrailer need to have sensors for monitoring and that they must be integrated with the tractor unit's monitoring system. A known solution to this problem is described in WO 2008/1210141, which relates to a monitoring and communication system for a vehicle (especially a long vehicle). Lamp units in the vehicle, for example warning lamps and position lamps, are provided with a communication unit and a monitoring sensor for wirelessly transmitting the output signal from the sensor to the central unit. Each sensor defines a monitoring zone for the detection of objects or movements within the monitoring zone. The sensor may be, for example, an ultrasonic sensor, a Doppler sensor, or a radar sensor. International Publication WO 2008/121041 describes a solution to the problem of how sensors for monitoring vehicles (especially in the case of long vehicles) will communicate with each other, and this solution involves the use of a wireless network. This can be supplemented by an additional lamp unit, for example arranged on the semitrailer. A disadvantage of the solution according to WO 2008/121041 is that it is relatively expensive in that components and techniques are required to adapt to the monitoring system of the tractor unit.

US 2006/0250230 describes a method of operating a monitoring and alarm device for a parked vehicle. The device includes a sensor unit for determining the distance between the vehicle and any approaching object in the active zone, and a reaction device connected to the control unit and activated when the object approaches the vehicle. The active zone is divided into at least an outer first subzone and an inner second subzone. The reaction device is gradually activated with respect to the amount, type, density and / or sequence in the first subzone, as compared with the activation with respect to the amount, type, density, and / or sequence in the second subzone.

US 2007/0205775 describes a device for capacitive determination of the position of an object by means of a plurality of capacitive probes distributed on the surface (to determine the position of the object relative to the surface). Is available). According to such a device, each probe can be connected to a voltage source and supplied a supply voltage through a coupling capacitance, and an evaluation device is provided to be connected to the probe to convert the probe signal into an output signal, the output signal being an object It serves as a measure of position.

Capacitive proximity sensors belong to a sensor category called proximity sensors that detect objects without contacting them. Examples of other proximity sensors are photoelectric and inductive proximity sensors. Capacitive proximity sensors detect objects based on their dielectric properties, and have many application areas that exploit these properties.

The main component of a capacitive proximity sensor is a capacitor plate (ie half of the capacitor). In short, a capacitor consists of two conductive plates separated by a dielectric material. The voltage difference applied to these plates creates an electric field across the dielectric material. This electric field stores the charges, and if there is no energy source, the electric field disappears and releases its energy in the form of a voltage, which gradually falls toward zero from the initial level. The ability of a capacitor to store charge is referred to as capacitance, measured in farads, the amount of which depends on the cross-sectional area of the capacitor plate, the distance between the capacitor plates, and the dielectric constant of the dielectric material. Water has a very high dielectric constant (about 80), while air has a low dielectric constant (about 1). The dielectric constant of most materials is between these values.

Thus, the capacitive sensor is half of the capacitor (ie capacitor plate). The object passing in front of the plate serves as another capacitor plate and as a dielectric material, and the capacitive sensor measures the capacitance resulting from this situation. Any such object with a dielectric constant different from that for air can be detected at least over short distances. Then, a measuring device can be provided for measuring the change in capacitance, and the measuring device can have certain threshold values set, for example, based on the distance between the object and the plate. Typical applications of capacitive sensors are in the food industry, where capacitive sensors are preferably used to detect whether a food container is full.

The capacitive proximity sensor can detect the object based on the object's ability (electrically charged). Since non-conductive materials can also be electrically charged, all objects can be detected with this type of sensor.

1 schematically illustrates an example of a capacitive sensor device that includes an oscillator, where a DC voltage is applied to the oscillator and the oscillator delivers AC current through the current sensor to the capacitor plate. The capacitor plate can retain charge because when the first plate is positively charged, the negative charge is attracted to the second plate, which allows more and more charge to be supplied to the first plate. . If both plates are present and close to each other, it is very difficult for one of them to carry a lot of charge. Thus, the capacitive sensor includes only one of the plates, and the AC current portion can only supply current from or carry current from this plate (which can have opposite charges nearby) If there is another plate). The object to be detected serves as the second plate. If the object is close enough to the sensor plate to be affected by the charge of the sensor plate, the object will acquire the opposite charge, and current can be supplied to the sensor plate and carried from the sensor plate, which current It can be measured by the sensor.

When capacitive sensors are used to detect objects around a vehicle, some of the disadvantages of such sensors are less important, for example, in that they do not detect directionality. The actual system has many sensors distributed at regular intervals along the outside of the vehicle. This means that whenever there is a sensor near an object (it is sufficient to be in a relatively limited range), the object can always be positioned by the sensor by positioning the sensor that detected the object. Means. The weak directional sensitivity is actually desirable in that it is very close to the vehicle and also enables detection of objects between the sensors.

Because of the weak directional sensitivity, capacitive sensors measure specific capacitance from objects in the environment (there is no concern because such environment is always present). When the sensor is mounted in a vehicle, the sensor detects the vehicle itself and external earth. Unknown objects are detected as this increase in background capacitance. However, at one meter distance, the change in capacitance is much smaller by a power of 10 than the background capacitance. This background capacitance must be determined so that it can be deducted from the measurement.

Because background capacitance is significant and drifts in relation to the capacitance of an object, it is much simpler to use the sensor to detect changes in the environment than to detect the absolute presence or absence of an unknown object. . The magnitude of the change in background capacitance depends on how stable the environment is.

In the mode of use of detecting change, the sensor should not be considered as a detector to detect presence, but rather as a detector to detect a change in presence.

A disadvantage of current alarm systems is that they are relatively complex and expensive to adapt to a vehicle in which a variety of different semitrailers can be combined. Moreover, current systems are often difficult to install on the bus (due to the large number of doors, storage hatches, etc.) and, as a result, are expensive to install.

It is an object of the present invention to provide a sensor system that is simple and inexpensive to install on both trucks and buses and does not require further modification, especially when the semitrailer is coupled to the truck.

The above object is achieved through the present invention as defined by the independent claims.

Preferred embodiments are defined through the dependent claims.

The present invention relates to a device for shell protection for a vehicle with or without a trailer / semi-trailer. The present invention uses a capacitive sensor system, which enables the detection of an invasion in an area created around the vehicle by the sensor. Such a sensor system is connected to the monitoring system of the vehicle, where the monitoring system provides alarms, for example using light or sound or via telematics. This technology protects the entire vehicle with any trailer or semitrailer.

The present invention achieves improved shell protection for tractor units with any trailer or semitrailer. Coupling the semitrailer to the tractor unit increases capacitance, but the sensor system automatically calibrates itself, so if the semitrailer is coupled, it is connected by a semitrailer that is also connected to the chassis earth of the tractor unit. Adjust yourself automatically.

Capacitive sensor systems make it possible to provide warning signals that can be adjusted to the extent of intrusion. It is also possible to retrofit an existing monitoring system into this system. The present system is also applicable to other vehicles (eg buses) and, for example, to mobile electric power plants, and many existing systems because the number of sensors can be reduced. Are simpler and therefore less expensive.

In short, the way this system works is that a person approaching a truck or semi-trailer increases the capacitance to ground. The result of this is a change in voltage, an increase in voltage divided into chassis earth and a virtual earth, and consequently a change in the measurement signal.

1 diagrammatically shows an example of a capacitive sensor device.
2 is a view schematically showing a truck having a semi-trailer in which the present invention is implemented.
3 is a block diagram of a capacitive sensor system according to the present invention.
4 shows measurement signals according to the invention.

2 is a schematic view of a truck with a semi-trailer in which the present invention is implemented. The capacitive sensor system comprises a signal generator, a signal detector and a processing unit, all of which are marked together as reference 1 and connected to the chassis earth 2 and via an earth antenna 4. Connected to the virtual external earth 3, where the chassis earth 2 is any earth point on the chassis of the vehicle.

The earth antenna 4 is, for example, a plate or cable located close to ground (external earth).

According to the invention, the earth antenna 4 in the form of a plate is fixed below the fuel tank, and is installed such that it is galvanically insulated from the fuel tank by, for example, a rubber mat or the like. The size of this type of antenna should be at least about 1 m 2 to achieve the desired sensitivity to the system, especially when implemented in a truck with a semitrailer. It is also possible to use the fuel tank itself as an antenna if the fuel tank is galvanically separated from the chassis and its size and distance from ground are sufficient. Where the earth antenna is fixed may also be other fastening points, for example any other suitable location under the silencer or under the vehicle.

The output signal from the processing unit is a reference value generated by measuring the potential difference ΔV between the chassis earth 2 and the external earth 3. The potential of the chassis earth changes when an object 5 (eg a person) approaches any portion connected to the chassis earth 2. By detecting this potential difference and detecting how it changes, it is possible to detect whether an object is close to the vehicle. The closer the object is, the greater the potential difference becomes, which makes it possible to detect the degree of intrusion (ie, how close the object is to the vehicle).

Since the combined trailer or semitrailer is electrically connected to the chassis of the vehicle, chassis earth for the trailer / semi-trailer may also be considered. Thus, the potential difference is also affected by an object approaching the trailer / semi-trailer.

The sensor system then communicates this intrusion, for example, electrically or wirelessly to the vehicle's monitoring system 6, which generates an alarm suitable for the detected situation.

Referring to FIG. 3, which is a schematic block diagram of a capacitive sensor system for a vehicle according to the invention, the sensor system includes a chassis earth, a signal generator, a signal detector, and a processing unit.

The signal generator is configured to generate a sensor signal (having frequency and amplitude) that is applied between the chassis earth 2 and the virtual external earth 3. The sensor signal preferably has a frequency in the range of 2 kHz to 20 kHz (eg, a frequency of 10 kHz) and an amplitude in the range of 2 V to 20 V (eg, an amplitude of 10 V). In order to ensure that measurements are made with the best possible signal-to-noise ratio, according to a preferred embodiment, so-called frequency hopping technology (e.g., the frequency varies according to a specific pattern) This includes.

The system also includes an earth antenna 4 that is electrically connected to the signal generator and configured to act as a virtual external earth 3. The earth antenna 4 is arranged in the vehicle to be electrically isolated from the chassis earth. The antenna has a predetermined size and is located at a predetermined distance from the ground surface.

The chassis earth has a capacitance of approximately nF for the truck and the same for the semitrailer, while the antenna plate (earth antenna 4) has a capacitance less than approximately 10 powers of about 10 (ie approximately 10 pF) to ground. (0.01 nF)). The earth antenna 4 should preferably have as large capacitance as possible with respect to ground.

According to a preferred embodiment, the earth antenna is configured to be mounted to the underside of the vehicle and comprises, for example, a metal plate having a flat surface, which is essentially horizontal to the underside of the vehicle (eg under the fuel tank). It is intended to be mounted. Other positions on the underside of the vehicle are of course also possible. The earth antenna may also include a plurality of plates electrically connected to each other. According to a further embodiment, the earth antenna is in the form of at least part or all of the fuel tank of the vehicle. Naturally, at least some or all of the fuel tanks must be insulated from the chassis earth.

As mentioned above, the earth antenna has a surface of at least 1 m 2 and preferably has a surface of about 1.5 m 2.

The shape of the earth antenna is not very important, but the distance from the ground and the exposed surface of the earth antenna is important. The larger the plate, and the closer it is to ground, the larger the (earth connection) capacitance. The capacitance between the earth antenna 4 and the reference earth (external earth) is preferably as large as possible.

The dimensions of the antenna depend on the (smallest allowable) capacitance difference between the chassis earth and the "antenna earth" (virtual external earth). The plate size is approximately 0.8 m x 1.6 m, which gives good results for trucks with semitrailers.

According to yet another embodiment, the earth antenna takes the form of an electrically insulated cable, which is configured to have an effective surface which in turn exhibits a capacitance corresponding to the capacitance of the metal plate.

The earth antenna is configured to be located at a predetermined distance within the range of 0.3 m to 0.8 m from the ground surface, where the earth antenna is provided with an electrically insulating layer (e.g. a rubber mat), where the earth insulating layer is provided with a vehicle. It is provided on the side facing the chassis of the vehicle when mounted on the vehicle. The distance between the plate (earth antenna 4) and the fuel tank is preferably about 10 mm, and the antenna is insulated by, for example, rubber mats or rubber spacers. What is important here is that the plate is galvanically separated from the tank, and means for preventing creep currents between the tank and the plate is adopted. The electrically insulating layer can protect both sides of the plate, but it is not necessary.

The size of the antenna and the distance to the ground surface are approximately 10 of 2, with the resultant capacitance (C1 in FIG. 3) to the ground surface (outer earth) being higher than the resulting capacitance (C2 in FIG. 3) between the vehicle's chassis and the ground surface. It is such a thing to make it smaller than a power. As the object (eg a person) approaches the vehicle, the capacitance C2 decreases.

The signal detector is configured to detect and determine the magnitude of the potential between the chassis earth and the external virtual earth, and generate and transmit a measurement signal to the processing unit based on this detection and determination.

The processing unit is configured to process the measurement signal and send the processed measurement signal to the alarm system, the alarm system to compare the processed measurement signal with one or more threshold levels and generate one or more alarm signals based on this comparison. It is composed. Alarm signals may include lamp signals (e.g. headlamps or interior lighting are switched on), acoustic signals (e.g. siren or vehicle). Horn), or signaling to an external alert center via, for example, a mobile network.

According to one embodiment, the processing unit processes the measurement signal by determining a derivative for the measurement signal, and in another embodiment, the processing unit generates an absolute value for the measurement signal. Process the measurement signal. According to another embodiment, the processing unit processes the measurement signal by amplifying the measurement signal and generating an absolute value for the measurement signal. According to one embodiment, the processing unit processes the measurement signal by determining a derivative for the change in the measurement signal. More complex forms of processing of the measurement signal are also possible, for example two different sliding mean values for the measurement signal (i.e. a slow moving average value suitable for the external environment and a fast movement which is the measurement signal itself). Level difference) can be determined. These are processed using various signal processing algorithms for useful signal acquisition. An example of a measurement signal with a slow moving average and a fast moving average is shown in FIG. 4. For signals with a slow moving average (solid line), the measurement is typically performed with the values detected for a time of at least 1 second. In the case of a fast moving average (dashed line), the measurement is carried out for a time of up to 50 ms over one millisecond. In this figure, the difference in amplitude A is indicated by a bidirectional arrow, and the derivative for each signal is also shown. Fast and reliable detection is achieved by comparing the difference in amplitude and / or difference in derivative at the same point in time with the appropriate thresholds.

In general, the relative change in capacitance between chassis earth and antenna earth (virtual external earth) is used.

The invention is not limited to the preferred embodiments described above. Various alternatives, modifications, and equivalents may be used. Accordingly, the foregoing embodiments should not be considered as limiting the protection scope of the invention as defined by the appended claims.

Claims (15)

A capacitive sensor system for a vehicle,
The system comprises a chassis earth 2, a signal generator 1, a signal detector 1, and a processing unit 1,
The signal generator 1 is adapted to generate a sensor signal applied between the chassis earth 2 and the virtual external earth 3, the sensor signal having a frequency and an amplitude,
The system comprises an earth antenna 4 which is adapted to serve as the virtual external earth 3, which is electrically connected to the signal generator 1 and is provided with a predetermined distance. Has a size and is electrically insulated from the chassis earth 2 and disposed in the vehicle to be located at a distance from the ground surface,
The signal detector 1 detects and determines the magnitude of the voltage between the chassis earth 2 and the virtual external earth 3 and generates a measurement signal based on the detection and determination to generate a measurement signal. 1) to deliver,
The processing unit 1 is adapted to process the measurement signal and to deliver the processed measurement signal to an alarm system 6,
The alarm system (6) is characterized in that it is arranged to generate one or more alarm signals based on the processed measurement signal. The method of claim 1,
The processing unit (1) is characterized in that for processing the measurement signal by determining the derivative of the measurement signal (derivative). The method of claim 1,
And said processing unit (1) processes said measurement signal by generating an absolute value of said measurement signal. 10. A method according to any one of the preceding claims,
Said alarm system (6) is arranged to compare said processed measurement signal with one or more threshold levels and generate one or more alarm signals based on said comparison. 10. A method according to any one of the preceding claims,
And the earth antenna (4) comprises a metal plate having a flat surface mounted horizontally on the underside of the vehicle. 10. A method according to any one of the preceding claims,
And the earth antenna (4) is adapted to be mounted on the underside of the vehicle. 10. A method according to any one of the preceding claims,
And the earth antenna (4) is adapted to be mounted on the underside of the fuel tank of the vehicle. 6. The method according to any one of claims 1 to 5,
And the earth antenna (4) is in the form of at least part of the fuel tank of the vehicle. 10. A method according to any one of the preceding claims,
The earth antenna (4) is characterized in that it is arranged at a predetermined distance from the ground surface in the range of 0.3 m to 0.8 m. 10. A method according to any one of the preceding claims,
The earth antenna (4) is characterized in that it has a surface of at least 1 m 2. 10. A method according to any one of the preceding claims,
The earth antenna 4 is provided with an electrically insulating layer, which is located on the face of the earth antenna 4 facing the chassis of the vehicle when the earth antenna 4 is mounted to the vehicle. Device characterized in that. The method of claim 1,
And wherein the earth antenna has a surface size such that the resulting capacitance to the ground surface is normally approximately 10 powers of two less than the resulting capacitance between the chassis of the vehicle and the ground surface. The method of claim 1,
And the earth antenna has the form of an electrically insulated cable. 10. A method according to any one of the preceding claims,
The device characterized in that the signal generator (1) is adapted to generate a sensor signal having a frequency in the range of 2 kHz to 20 kHz and an amplitude in the range of 2 V to 20 V. 15. The method of claim 14,
Wherein said signal generator is adapted to generate a sensor signal having a frequency of 10 kHz and an amplitude of 10 volts.

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