DE19724168C1 - Body presence detection device, especially for motor vehicle - Google Patents

Abstract

The device detects the presence of a body, especially a human body, in a detection area (136) through a capacitive sensor (160) which includes an electrode arrangement (148). The electrode arrangement is connected to a detection circuit, and its capacitance is changed through the entry of the body in the detection area (136). The capacitive sensor (160) includes a body (156) from electrically conductive material, which is electrically separated from the electrode arrangement. Capacitively induced charges are produced in the body, through an electric charge applied to the electrode arrangement. The body is preferably arranged outside the detection area.

Description

The present invention relates to a device for De detection of the presence of a body, especially one human body, in a detection area, with a capacitive sensor, which comprises an electrode arrangement, which can be connected to a detection circuit and their Capacity by inserting the body into the detection area is changeable.

Such devices can be used in particular for who to recognize the occupancy of a seat in a vehicle and depending on the seat occupancy safety device such as an airbag system, warning devices such as a belt warning indicator or other setup activations of the vehicle.

A device of the type mentioned is known from German patent 44 17 827 C2. In this known device, two flat measuring electrodes are arranged side by side in the seat of a seat. The two measuring electrodes produce, when connected to voltage, an electric field in a detection area arranged above the seat surface of the seat, which can be influenced by the presence of a person in the detection area. The capacity of an electrode arrangement depends linearly on the relative dielectric constant ε _{r of} the material with which the space which is penetrated by the electric field of the electrode arrangement is filled. Since human tissue is about 75% water, which has a high relative dielectric constant of about 80, the capacity of the electrode arrangement in the state in which a person is in the detection area is compared to the capacity of the electrode arrangement in the state , in which the seat is not occupied, increased. The capacity of the electrode arrangement in the state in which there is no body to be detected in the detection area is referred to below as the resting capacity of the electrode arrangement.

The by inserting a body to be detected in the Detection range achievable capacity change is in the we considerably proportional to the resting capacity of the electrodes arrangement. The be from German patent 44 17 827 However, the known electrode arrangement has only a small one Resting capacity (typically up to 50 pF) on that is smaller than the capacity of the leads of the electrodes arrangement (typically 200 pF). By bringing in of a body to be detected in the detection area targetable absolute changes in capacitance of the electrode arrangement are therefore of the same order of magnitude as the capacitance act of the leads to the electrode assembly, so that the achievable capacity change in relation to the total capacitance of the capacitive sensor resulting from the capacitance  the electrode arrangement and the capacity of the leads composed, comparatively small and therefore difficult to detect is animal. Due to the low resting capacity of the Electrode arrangement can therefore lead to errors in the detection tion of the presence of a body in the detection area come.

The present invention is therefore based on the object to create a device of the type mentioned at by inserting a body to be detected into the detection area a higher change in capacity Electrode arrangement can be reached.

This task is called in a device of the beginning ten kind solved according to the invention in that the capacitive Sensor an influence body made of electrically conductive mate rial comprises, the ge of the electrode assembly electrically is separated and at which electrical influence charges through electrical charges arranged in the electrode arrangement are witnessable.

Electrical charges arise on the electrode arrangement, if the electrode arrangement, for example by means of the De tection circuit, with an electrical voltage is struck.

The concept according to the invention is based on the knowledge that that the resting capacity of an electrode arrangement differs can significantly increase an influencing effect. For exploitation this influence effect is an influence body made of electricity  conductive material, the elec is separated sufficiently close to the electrode arrangement Provide voltage so that electrical In Fluence charges due to the effect of the electrode arrangement arranged electrical charges arise.

This creates in an area of the influential body, the egg be in the area of the electrode arrangement with positive charge is neighboring, a negative influenza charge. In one area of the influence body, which is an area of the electrode arrangement is adjacent to the negative charge, a posi arises tive influenza charge. The adjacent charges of the Electrode arrangement on the one hand and the influence body on the other on the other hand, they have opposite polarity. Therefore is the electric field generated by the influential charges is generated outside of between the electrode assembly and the area lying opposite the influential body that generated by the charges on the electrode assembly electric field directed. Because of the superposition of both Fields there is a weakening of the electrical Field of the electrode arrangement. However, if the electrical Potentials of the areas of the electrode arrangement are fixed ben are, for example, in that between two electric external electrode voltage is placed, flow to compensate for the weakening of the electric field due to the influence of further charges on the electrodes. Increased by the influence of the influence the electrical charge on the electrodes of the elec electrode arrangement with fixed voltage; This matches with an increase in the capacity of the electrode arrangement.  

So that the influenza charges can develop undisturbed, the influence body of all is more electrically conductive. Kör pern in its environment, especially from live Lei lines, electrically separated, preferably by insulating bodies electrically isolated. Thus the body of the influence is located not at a fixed electrical potential; rather, the potential of the influential body may be due to of the influence of the influence depending on the potential freely adjust the electrodes of the electrode arrangement.

The influence of the influence can increase the resting capacity the electrode arrangement by a factor of up to 25 be enough. Because of this significant increase in The device according to the invention is then also resting capacity can be used if the electrical system is in the immediate vicinity the arrangement of the capacitive sensor live lines are arranged, which are connected to a ground potential. Such live cables set the resting capacity of the Electrode assembly down; by the influence of the influence Capacity increase achieved according to the invention makes this a but more than make up for it. The device according to the invention is therefore particularly suitable in addition to a seat heater to be arranged in a seat, the occupancy detek should be animals.

The by inserting a body to be detected in the Detection area achieved change in capacitance of the electrodes arrangement is increased by the effect of influence as well  the resting capacity of the electrode arrangement. With the inventor device according to the invention can therefore absolute capaci Educate changes in the capacity of the electrode assembly len, which are significantly larger than the capacity of the supply capacitive sensor.

Basically, the influential body can be relative to any position occupy the detection area. Preferably, the In however, the fluid body is arranged outside the detection range net. This ensures that the detection range in that area of the electric field of the electrodes order lies in which the fields of the charges on the electrical the arrangement and the fields of the influence charges each other are directed in opposite directions.

It has proven to be particularly favorable if the In fluence body on a surface facing away from the detection area Side of the electrode arrangement is arranged. Such an approach Order leads to a large change in the capacity of the electrical system the arrangement when introducing a dielectric into the detector area.

In a preferred embodiment of the invention The device covers the body of the influence of the detection completely away from the side of the electrode arrangement.

About the type of electrode arrangement used were before standing no details given yet.  

Basically, it is conceivable that the electrode arrangement has only one electrode, the capacity with respect to a Reference potential, for example a grounded vehicle housing, is measured.

However, the electrode arrangement preferably comprises at least two electrodes that are electrically separated from each other different electrical potentials are placed can.

The influential body is advantageously trained in this way det and arranged that by the electric charge everyone Electrode influence charges can be generated on your influence body are.

It is particularly favorable if the electrode arrangement has a Symmetry, for example mirror symmetry with respect to egg ner mirror plane, and the influence body so out forms and is arranged that it has the same symmetry, at for example a mirror symmetry with respect to the same mirror gel level.

The at least two electrodes of the electrode arrangement can arranged on different sides of the detection area be. In this case it is an advantage if each electrode an influence body is assigned, which is preferably in each case on the side facing away from the detection area fenden electrode is arranged.  

A more compact structure of the electrode arrangement and thus that capacitive sensor of the device according to the invention reached when the electrodes of the electrode arrangement in the we noticeably flat and in one, preferably in essential flat, electrode layer arranged side by side are not. In this case, the at least two electrodes the electrode arrangement on the same side of the detection area Reichs arranged so that a one-piece In fluenzkörper can be used to uni the influencing effect for to use both electrodes.

By a suitable geometry of the electrodes of the electrodes arrangement can the rest capacity of the electrode arrangement knows ter be increased.

With a favorable to achieve a high resting capacity The arrangement has two electrodes each of the electrode arrangement because the shape of a comb with several prongs on and are these electrodes are arranged so that the Interlock the teeth of the two electrodes.

As particularly cheap to achieve a high resting capacity However, it has been found that the electrode arrangement comprises at least one meandering electrode. Includes the Electrode arrangement several electrodes, so it is from before part if all electrodes of the electrode arrangement meander have a shape.

In a preferred embodiment of the invention The device is the influencer body, preferably in the essentially level, influenza layer. Such  Influence layer can in particular be flexible, so that it can deform non-destructively if one too Detecting body introduced into the detection area is, for example the seat, the occupancy detek is to be documented.

For the desired increase in the resting capacity of the electrodes arrangement, it is particularly favorable if the electrode arrangement voltage arranged side by side in an electrode layer covers flat electrodes and the influence body as in the we Substantially formed in parallel to the electrode layer fluence layer is formed.

The required electrical separation of the electrode arrangement This can, for example, result from the influence body be enough that an air-filled or evacuated intermediate space between the electrode arrangement and the influenza body is provided.

A more reliable separation, even with a deformation of the capacitive sensor for sufficient insulation provides, but is achieved when between the electrodes order and the influence body an electrically non-conductive ger insulation body is arranged.

The resting capacity of the electrode arrangement depends on the Influence effect among other things from your distance between the electrode arrangement and the influence body. If the between the electrode arrangement and the influence body seen insulation body is elastically deformable, can this effect for a further increase in through the  Introducing a body achievable in the detection area Capacity changes can be exploited. Is namely in one in such a case the capacitive sensor introduced by the Body subjected to mechanical pressure, so ver the distance between the electrode arrangement and decreases the influence body due to the elastic deformation of the Isolation body, which is an additional increase in Kapa result of the electrode arrangement.

To evaluate the by inserting a body in the De tection area caused electrical capacity change The arrangement according to the invention has the advantage has a detection circuit which has an on Direction for generating one of the current total capacities of the capacitive sensor corresponding measurement signal.

Such a detection circuit can consist of discrete electronics be built components or a program mable processor with a suitable evaluation program include.

For the intended detection purpose of the invention The only thing that matters is the most accurate He possible Detection of the change in capacitance of the electrode arrangement. It is therefore advantageous if the detection circuit is an on direction for generating a total resting capacity of the ka capacitive sensor corresponding reference signal and Device for reducing the amount of the measurement signal by Amount of the reference signal includes. The total resting capacity of the capacitive sensor consists of the resting capacitance act of the electrode arrangement and the capacity of the between  the detection circuit and the electrode arrangement neten supply lines together. Through the one described above Measure is therefore achieved that the amount of the Refe renzsignals reduced measurement signal directly by a in body introduced into the detection area generated capaci change of state corresponds.

In many applications, it is desirable that the device for detecting the presence of a body in the detection area be able to distinguish between different groups of introduced bodies. For this purpose, the detection circuit advantageously comprises a device for generating a detector output signal which indicates whether the measurement signal exceeds a predetermined threshold value. As a result, it is possible to have the device according to the invention only indicate the presence of a body in the detection area if it causes a change in capacitance in the electrode arrangement which is above a predetermined minimum value. In this way, in particular human bodies, which have a high average relative permittivity ε _r due to the high proportion of water in human tissue and therefore cause comparatively high changes in capacitance in the electrode arrangement, of objects which consist essentially of plastic or metal and are therefore essential have lower average relative permittivities ε _r .

It is also advantageous if the device for generating egg Nes detector output signal is designed so that the  same generated output signal at a lower or The measurement exceeds the specified threshold signal only changes if the minimum or high limit is exceeded lasts for a predetermined period of time. To this This can prevent the detector output from moving signal changes when a body is in the De for only a short time tection area introduced or only for a short time from the Detection range is moved. For example conceivable that a person occupying a seat whose Bele tion detected by a device according to the invention should rise from the seat for a short time, by about to reach behind the seat or one outside their realm wide operating device in the sitting position to reach. In such a case, it is usually him wishes the detection device to continuously receive a Occupancy of the seat in question.

In addition to recognizing the occupancy of a seat, the inventor device according to the invention also for any other applications be used in which the presence of a body in a detection area is to be detected. For example can the device for detecting the occupancy of patients serve beds.

Since in the device according to the invention by the influence effect due to the proximity of live cables to the capacitive sensor-related decrease in the resting capacity is settled, the device according to the invention is suitable especially as part of a heating device, in particular a seat heater to be used, the  Heating device in addition to the device according to the invention Heating element and a heating control for controlling a heater power supply to the heating element depending on a De tector output signal of the device according to the invention sums up. Such a heating device can be operated in this way be that the heating control the heating current supply to the Heating element only releases when the detector output signal indicates that a human body in the detec tion range, for example on the one to be heated Seat that is present. Compared to a seat heater that heated a seat regardless of its occupancy, can considerable energy savings can be achieved.

A heating element and a detection device for Er identification of a seat occupancy comprehensive seat heating that only is switched on when the seat is occupied, is off DE 41 10 702 A1 known. This known seat heating includes however, no detection device according to one of the claims  1 to 15.

As a rule, the detection range is essentially that correspond to the area to be heated by means of the heating device chen. It is therefore advantageous if the heating element between the electrode arrangement of the device according to the invention and the detection area is arranged, since the Heizele ment in the immediate vicinity of the area to be heated ches. In a preferred embodiment of the heating device is provided that the heating device Heating mat comprises, in which the heating element, the electrodes order and the influential body are arranged. By the In  tegration of the heating element, the electrode arrangement and the Influence body in the heating mat becomes a compact structure and enables a time-saving installation of the heating device.

A further reduction in the space requirement of the heater and a further reduction in the assembly time required can be achieved in that the heating control and the Detek tion circuit of the device for detecting the presence  of a body in the detection area in a common Housing are arranged.

Other features and advantages of the invention are the subject the following description and graphic representation second embodiments.

The drawings show:

Figure 1 is a schematic representation of a Heizvor direction, in which a device for detecting the presence of a body is integrated.

Fig. 2 is a seat, for example a vehicle seat, in which a mat of Heizvorrich processing of Figure 1 is integrated.

Fig. 3 is a schematic, greatly inflated cross section through the heating mat of the Heizvorrich device of Figure 1, in which a heating element layer, an electrode layer and a fluence layer in the heating mat are shown.

Figure 4 is a schematic longitudinal section through the heating element layer of the heating mat of the Heizvor direction of Fig. 1.

Figure 5 is a schematic longitudinal section through the electrode layer of the heating mat of a first embodiment of the heater of FIG. 1.

Fig. 6 is a schematic longitudinal section through the influence layer of the heating mat of the Heizvor direction of Fig. 1;

Fig. 7 is a block diagram of a detection circuit of the apparatus for detecting the presence of a body;

FIG. 8 shows a time course of an output voltage of a triangular generator of the detection circuit from FIG. 7;

Fig. 9 shows a time course of an output voltage of the one-way amplifier of the detection circuit of Fig. 7;

FIG. 10 shows a time course of an output voltage of a DC voltage converter of the detection circuit from FIG. 7;

Fig. 11 is a schematic longitudinal section through the electrode layer of the heating mat of a second embodiment of the heater.

All figures have the same or functionally equivalent Elements with the same reference numerals.

A heating device shown schematically in FIG. 1, designated as a whole by 100 , comprises a flexible, flat, essentially rectangular heating mat 102 .

The heating mat 102 has a heating current input 104 , which is connected via a heating current supply line 106 to a heating current output 108 of a heating controller or a heating controller 110 .

Furthermore, the heating mat 102 has a heating current output 112 which is connected to a ground potential via a heating current discharge line 114 .

Furthermore, the heating mat 102 has a detection current input 116 , which is connected via a detection current supply line 118 to a detection current output 120 of a detection circuit 122 , and a detection current output 117 , which is connected via a detection current discharge line 119 to a detection current input 121 of the detection circuit 122 .

The heating controller 110 and the detection circuit 122 are accommodated in a common housing 124 which is connected to a power source, for example a motor vehicle battery, via a supply cable (not shown).

As shown in FIG. 2, the heating mat 102 of the heating device 100 can be arranged in a seat cushion 126 of a seat 128 of a means of transport, for example a motor vehicle, in order to be able to heat a seat surface 130 of the seat 128 .

Alternatively or in addition, the heating mat 102 can also be arranged in a backrest 132 of the seat 128 in order to be able to heat a leaning surface 134 of the seat 128 .

In both cases, it is for reasons of energy saving that he wishes that the heating mat 102 is only supplied with a heating current when the seat 128 is occupied by a person, for example a driver or passenger, that is, a human body in which Fig. 2 is shown in broken line detection area 136 . For this purpose, the heating device 100 comprises a device for detecting the presence of a body in the detection area 136 , which generates an output signal which indicates whether the seat 128 is occupied and by means of which the heating controller 110 controls the supply of heating current to the heating mat 102 . This device for detecting the presence of a body is described in more detail below.

As shown in Fig. 3, the heating mat 102 comprises an upper insulation layer 138 , which faces the seat 130 in the installed state and consists of an electrically non-conductive film or an electrically non-conductive fabric.

At the top of this upper insulation layer 138 is a heating element layer 140 , in which a linear heating element 142 having the shape of a heating coil is arranged. The shape of the heating element 142 can be seen from the longitudinal section of FIG. 4.

Instead of a heating element in the form of a heating wire can for example, a carbon mat as a heating element be used.  

A first end of the heating element 142 is connected to the heating current input 104 of the heating mat 102 , while a second end of the heating element 142 is connected to the heating current output 112 of the heating mat 102 . If a heating current flows from the heating current input 104 to the heating current output 112 of the heating mat 102 , heat is generated in the heating element 142 due to its ohmic resistance and is emitted through the upper insulation layer 138 to the seat surface 130 .

At the bottom of the heating element layer 140 of the heating mat 102 is an intermediate insulation layer 144 , which consists of an electrically non-conductive foil or an electrically non-conductive fabric.

An electrode layer 146 adjoins the intermediate insulation layer 144 , in which an electrode arrangement 148 is arranged.

The electrode arrangement 148 comprises a planar, meandering first electrode 150 , and a planar and meandering second electrode 152 , which is arranged in the same plane as the first electrode 150 substantially parallel to it at a distance of approximately 5 mm, for example .

The two electrodes 150 and 152 consist of a material with good, preferably metallic conductivity, for example a silver-plated copper braid, and each have a width (measured along the electrode layer 146 ) of, for example, approximately 30 mm and one (perpendicular to the electrode layer 146 measured) thickness of about 0.2 mm, for example.

One end of the first electrode 150 is connected to the detection current input 116 of the heating mat 102 . One end of the second electrode 152 is connected to the detection current output 117 of the heating mat 102 .

The space between the two electrodes 150 and 152 is preferably filled with air, but may also contain an electrically insulating material.

At the bottom of the electrode layer 146 is another intermediate insulation layer 154 , which consists of an elastically deformable, electrically non-conductive film or an elastically deformable, electrically non-conductive fabric. The thickness of this intermediate insulation layer is, for example, 0.8 mm.

At the bottom of the intermediate insulation layer 154 is an influential layer 156 , which consists of a material with good, preferably metallic conductivity and extends parallel to the layer interfaces at least as far as it extends the electrode arrangement 148 of the electrode layer 146 , the parallel projection of which is perpendicular to one another the direction of the layer direction on the influenza layer 156 in FIG. 6 is shown in broken lines. The fluence layer 156 thus completely covers the side of the electrode arrangement 148 facing away from the detection region 136 .

Influence layer 156 may consist of a metal foil or, like electrodes 150 and 152 of electrode arrangement 148 , of a silver-plated copper braid.

A lower insulation layer 158 of the heating mat 102 adjoins the influencing layer 156 at the bottom and consists of an electrically non-conductive material, for example an electrically non-conductive film or an electrically non-conductive fabric.

If the heating mat 102 is arranged during installation so that it rests on a body made of electrically non-conductive material, for example a foam cushion of the seat 128 , the lower insulation layer 158 of the heating mat 102 can be omitted.

The electrode arrangement 148 , the detection current lines 118 and 119 , the influence layer 156 and the intermediate insulation layer 154 arranged between the electrode arrangement 148 and the influence layer 156 together form a capacitive sensor 160 , the function of which will be explained in more detail below.

If, for example, the first electrode 150 is placed on a positive and the second electrode 152 of the electrode arrangement 148 on a negative potential, then a positive net charge arises on the first electrode 150 and a negative net charge on the second electrode 152 . The positive net charge on the first electrode 150 generates a negative influenza charge in the region of the influencing layer 156 adjacent to the first electrode 150 . Similarly, the net negative charge at the second electrode 152 generated in the second electrode 152 adjacent the region of the induction layer 156 as great a positive influence charge.

By superposition of the electric fields of the net charges on the electrodes 150 and 152 and the influence charges in the influence layer 156 , an overall electrical field is created, the field lines of which extend far into the detection area 136 arranged above the electrode arrangement 148 .

Because of the effect of the influence charges, larger charges on the electrodes 150 and 152 are required to generate an electric field corresponding to the predetermined potential difference between the electrodes 150 and 152 than would be the case without the presence of the influence charges.

Due to the influence of the influence, the rest capacitance C _{O, I of} the electrode arrangement 148 in the presence of the influent layer 156 is therefore significantly higher than the rest capacitance C _{O of the} same electrode arrangement 148 without the influence layer 156 . The quiescent capacitance C _{O, I} or C _O is understood to mean that capacitance of the electrode arrangement 148 which results when there is no dielectric body in the detection region 136 .

If a dielectric is introduced into the detection region 136 , the capacitance of the electrode arrangement 148 changes by an amount which is essentially proportional to the dielectric constant of the dielectric in question and to the rest capacitance. Therefore, the capacitance change ΔC _I which can be achieved by introducing a dielectric in a capacitive sensor 160 with an influence layer 156 is greater than in a conventional capacitive sensor which does not include an influence layer.

An increase in the resting capacity of the electrode arrangement 148 has a particularly advantageous effect if the electrode arrangement 148 carries current in the immediate vicinity of the lines connected to the ground potential, since the vicinity of such lines, for example the heating element 142 in the heating element layer 140 , has the resting capacity of electrode assembly 148 is reduced. The influencing effect counteracts the reduction in the resting capacity of the electrode assembly 148 through the heating element 142 and it makes it possible to arrange the capacitive sensor 160 and the heating element 142 in close proximity to one another in the heating mat 102 .

The change in capacitance ΔC _{I of} the electrode arrangement 148 is detected and evaluated by means of the detection circuit 122 shown as a block diagram in FIG. 7.

The detection circuit 122 and the capacitive sensor 160 together form a device 164 for detecting the presence of a body in the detection area 136 .

The detection circuit 122 comprises a triangle generator 170 , which generates a triangular AC output voltage with a frequency of, for example, 5 kHz to 20 kHz. The output signal 177 of the triangle generator 170 is shown in Fig. 8, in which the output voltage U of the triangle generator 170 is plotted against the time t.

Instead of a triangle generator, a sine generator can also be used be used with a sinusoidal output change voltage with a frequency of, for example, 15 kHz to 25 kHz generated.  

The triangle generator 170 is connected to the first electrode 150 of the capacitive sensor 160 via an intermediate line 172 , the detection current output 120 of the detection circuit 122 , the detection current supply line 118 and the detection current input 116 of the heating mat 102 .

The second electrode 152 of the capacitive sensor 160 is connected via the detection current output 117 , the detection current discharge line 119 , the detection current input 121 of the detection circuit 122 and an intermediate line 174 to an input of a one-way amplifier 176 .

The intermediate line 174 is connected to the ground potential via a resistor 178 . The capacitive sensor 160 and the resistor 178 together form a differentiator 180 for the output signal of the triangular generator 170 .

The input signal of the one-way amplifier 176 therefore corresponds to a rectangular AC voltage, the amplitude of which is essentially proportional to the capacitance of the capacitive sensor 160 .

The one-way amplifier 176 cuts off the negative signal components of the input signal and increases the amplitude of the positive signal components uni a factor V of, for example, 2.5, so that its output signal 179 receives the pulsed form shown in FIG. 9.

The output of the one-way amplifier 176 is connected via an intermediate line 182 to an input of a DC-DC converter 184 .

The DC-DC converter generates a DC voltage output signal 183 from its pulsed input signal, the amplitude of which corresponds to the instantaneous total capacitance of the capacitive sensor 160 . This output signal 183 is shown in FIG. 10.

An output of the DC / DC converter 184 is connected via an intermediate line 185 to a non-inverting input of a differential amplifier 186 .

An inverting input of the differential amplifier 186 is connected via an intermediate line 187 to a branch point 188 of a voltage divider 190 , which stood between a first divider resistor 192 and a second divider resistor 194 of the voltage divider 190 .

The second divider resistor 194 is connected to the ground potential, while the first divider resistor 192 is connected via a feed line 195 to a stabilized voltage source 196 of the detection circuit 122 .

The ratio of the ohmic resistances R ₁ and R _{2 of} the first divider resistor 192 and the second divider resistor 194 of the voltage divider 190 is selected so that the input voltage tapped at the branch point 188 at the inverting input of the differential amplifier 186 of the total quiet capacitance of the capacitive sensor 160 ( including the capacity of the detection current lines 118 and 119 ) speaks ent. As long as the capacitive sensor 160 is in its idle state, that is, as long as there is no body to be detected in the detection area 136 , the input voltages at the inputs of the differential amplifier 186 are therefore equal to one another, so that the differential amplifier outputs the output voltage zero.

However, if a dielectric body is introduced into the detection region 136 , the capacitance of the electrode assembly 148 and thus the capacitance of the capacitive sensor 160 increases by the amount ΔC, so that in this case the DC converter 184 outputs a voltage which is greater than the reference voltage applied to the inverting input of the differential amplifier. The differential amplifier 186 in this case outputs a positive output voltage, the amount of which is proportional to the change in capacitance of the electrode arrangement 148 caused by the dielectric body.

The output of the differential amplifier 186 is connected via an intermediate line 198 to an input of a trigger stage 200 .

A signal output of the trigger stage 200 is connected via a signal line 202 to a (not shown) signal input of the heating controller 110 .

The trigger stage 200 generates a digital output signal, which depends on whether the voltage present at the input of the trigger stage 200 is above or below a predetermined threshold voltage value.

The voltage present at the input of the trigger stage 200 is essentially proportional to the change in capacitance ΔC of the electrode arrangement 148 . As long as no dielectric body is introduced into the detection region 136 , this voltage is essentially zero. If a dielectric body is introduced into the detection area 136 , there is a change in capacitance ΔC of the electrode arrangement 148 , which essentially depends on the spatial extent of the body in question and its relative dielectric constant ε _r .

If the body introduced into the detection area 136 loads the seat surface 130 of the seat 128 with its weight, there is also a weight-dependent change in capacitance, since the elastic intermediate insulation layer 154 arranged between the electrode arrangement 148 and the influence layer 156 presses together by the weight of this body becomes, which reduces the distance between the electrode arrangement 148 and the influent layer 156 and leads to an increase in the capacitance of the electrode arrangement 148 .

Compared to objects that are usually placed on the seats of a means of transport, human bodies have a large spatial dimension, high weight and a high relative permittivity ε _r , since approximately 75% of human tissue consists of water, the relative permittivity ε _{r of which} is approximately 80, while the relative permittivities of glass are approximately 10, paper approximately 5, rubber approximately 2.6 and air and other gases approximately 1.

Comparative tests have shown that even children who sit on the seat 128 cause a significantly higher capacity change in the electrode arrangement 148 than objects which are usually placed on such a seat 128 , such as, for example, cable reels, notebooks, tool boxes, hand luggage, cell phones, Metal or plastic cases, books, clothing, soda boxes, beverage cartons or shopping bags.

It is therefore possible to select a threshold value for the input voltage of the trigger stage 200 proportional to the change in capacitance of the electrode arrangement 148 , which threshold value is always exceeded when a person takes a seat on the seat 128 , but is not reached when objects such as those listed above by way of example the seat 128 abge. If this threshold voltage value is exceeded, the trigger stage 200 outputs a digital signal which indicates the presence of a person in the detection area 136 , that is to say an occupancy of the seat 128 . If, however, this threshold voltage value is not reached at the input of the trigger stage 200 , the trigger stage 200 outputs a digital signal which indicates the absence of a person from the detection area 136 , that is to say an unoccupied seat 128 .

The trigger stage 200 is provided with a delay device, which ensures that the output signal of the trigger stage 200 only changes if the threshold voltage value of the input voltage of the trigger stage 200 is exceeded or undershot for a predetermined period of time, preferably several seconds. This delay device prevents the output signal of the trigger stage 200 from changing due to brief fluctuations in the capacitance of the electrode arrangement 148 , for example when a person occupying the seat 128 gets up briefly or when driving through a vibration path. Short-term changes in the output signal of the trigger stage 200 are undesirable because they lead to unnecessary switching of the switching element evaluating the output signal of the trigger stage 200 , for example the heating controller 110 .

The heating controller 110 controls the heating current through the heating mat 102 in dependence on the output signal of the trigger stage 200 in such a way that the heating current supply is interrupted when the output signal indicates that the seat 128 is not occupied, while a heating current is supplied when the output signal is a Occupancy of the seat 128 indicates and the heating device 100 , for example by means of a switch arranged on a dashboard of the means of transport, is switched on. By interrupting the heating current supply when the seat is not occupied, unnecessary heating of the seat 128 is avoided and the energy balance of the heating device 100 is improved.

The triangle generator 170 , the one-way amplifier 176 , the differential amplifier 186 and the trigger stage 200 of the detection circuit 122 are supplied with the required supply voltage by the stabilized voltage source 196 via supply lines 195 .

In the above described detection circuit 122, a change in capacitance of the electrode assembly 148 ent speaking measurement signal is generated by the fact that the capacitive sensor as a capacitor 160 inte in a high pass filter 180 is grated. As an alternative or in addition to this, it would also be possible to integrate the capacitive sensor 160 in a resonant circuit and to measure a change in the resonant frequency of the resonant circuit determined by the capacitance of the capacitive sensor 160 . Any other method suitable for determining a change in capacity can also be used.

The device 164 described above for detecting the presence of a human body in a detection area 136 can be used in addition to controlling the heating device 100 also for controlling other devices which are to be activated or de-activated depending on the occupancy of the seat 128 . Thus, the stop can output signal of the trigger stage 200, for example, to USAGE det are an enable 128 associated airbag system the seat when this output signal zes an occupancy of the sit displays 128, or trigger a Gurtwarnsignal, when the output signal indicative of an occupancy of the seat 128, by a predetermined time interval but a seat belt assigned to seat 128 has not been fastened.

A second embodiment of a heating device 100 with an integrated device 164 for detecting the presence of a human body in the detection area 136 differs from the first embodiment described above with regard to the configuration of the electrode arrangement 148 .

As shown in FIG. 13, the electrode arrangement 148 of the second embodiment comprises a first electrode 150 and a second electrode 152 , both of which have the shape of a comb with a plurality of prongs 206 and are arranged in the electrode layer 146 of the heating mat 102 in such a way that one another the prongs 206 of the first electrode 150 and the prongs 206 of the second electrode 152 interlock.

Otherwise, the second embodiment of the heating device 100 is identical in structure and function to the first embodiment described above.

Claims (19)

1. Device for detecting the presence of a body, in particular a human body, in a detection area ( 136 ),
with a capacitive sensor ( 160 ) which comprises an electrode arrangement ( 148 ) which can be connected to a detection circuit ( 122 ) and whose capacitance can be changed by introducing the body into the detection area ( 136 ),
characterized in that the capacitive sensor (160) comprises a Influenzkörper (156) of electrically conductive material which is electrically separated from the electrode assembly (148) and to the electric influence charges carried on the electrical end assembly (148) arranged electrical charges he is zeugbar . 2. Device according to claim 1, characterized in that the influent body ( 156 ) outside of the detection area ( 136 ) is arranged. 3. Apparatus according to claim 2, characterized in that the influence body ( 156 ) is arranged on a side of the electrode arrangement ( 148 ) facing away from the detection area ( 136 ). 4. The device according to claim 3, characterized in that the influence body ( 156 ) covers the detection area ( 136 ) facing away from the electrode arrangement ( 148 ) completely dig. 5. Device according to one of claims 1 to 4, characterized in that the electrode arrangement ( 148 ) comprises at least two electrically separate electrodes ( 150 , 152 ). 6. The device according to claim 5, characterized in that the electrodes ( 150 , 152 ) of the electrode arrangement ( 148 ) are substantially planar and are arranged next to one another in a, preferably substantially planar, electrode layer ( 146 ). 7. The device according to claim 6, characterized in that two electrodes ( 150 , 152 ) of the electrode arrangement ( 148 ) each have the shape of a comb with a plurality of prongs and are arranged relative to one another such that the prongs of the two electrodes ( 150 , 152 ) interlock. 8. Device according to one of claims 1 to 7, characterized in that the electrode arrangement ( 148 ) comprises at least one meandering electrode ( 150 , 152 ). 9. Device according to one of claims 1 to 8, characterized in that the influence body is designed as a, preferably preferably substantially flat, influence layer ( 156 ). 10. Device according to one of claims 1 to 9, characterized in that an electrically non-conductive insulation body ( 154 ) is arranged between the electrode arrangement ( 148 ) and the influence body ( 156 ). 11. The device according to claim 10, characterized in that the insulating body ( 154 ) is elastically deformable. 12. Device according to one of claims 1 to 11, characterized in that the detection circuit ( 122 ) comprises means ( 170 , 180 , 176 , 184 ) for generating a measurement signal corresponding to the instantaneous total capacitance of the capacitive sensor ( 160 ). 13. The apparatus according to claim 12, characterized in that the detection circuit ( 122 ) means ( 190 , 196 ) for generating a reference signal corresponding to a total capacitance of the capacitive sensor ( 160 ) and means ( 186 ) for reducing the amount of the measurement signal by Amount of the reference signal includes. 14. Device according to one of claims 12 or 13, characterized in that the detection circuit ( 122 ) comprises means ( 200 ) for generating a detector output signal, which indicates whether the measurement signal exceeds a predetermined threshold. 15. The apparatus according to claim 14, characterized in that the device ( 200 ) for generating a detector output signal is designed so that the output signal generated by the same ben changes when the measured signal falls below or exceeds the predetermined threshold value only if the Falling below or exceeding lasts for at least a predetermined period of time. 16. A heating device, in particular a seat heating device, comprising a heating element ( 142 ), a device ( 164 ) for detecting the presence of a body in a detection area ( 136 ) according to one of Claims 1 to 15 and a heating control ( 110 ) for controlling a Heating current supply to the heating element ( 142 ) in response to a detector output signal of the device ( 164 ) for detecting the presence of a body in the detection area ( 136 ). 17. Heating device according to claim 16, characterized in that the heating element ( 142 ) between the electrode arrangement ( 148 ) of the device ( 164 ) for detecting the presence of a body in the detection area ( 136 ) and the detection area ( 136 ) is arranged. 18. Heating device according to one of claims 16 or 17, characterized in that the heating device ( 100 ) comprises a heating mat ( 102 ) in which the heating element ( 142 ), the electrode arrangement ( 148 ) and the influence body ( 156 ) are arranged. 19. Heating device according to one of claims 16 to 18, characterized in that the heating control ( 110 ) and the detection circuit ( 122 ) of the device ( 164 ) for detecting the presence of a body in the detection region ( 136 ) in a common housing ( 124 ) are arranged.