KR20080012259A - Capacitive sensor and method of production - Google Patents

Abstract

The invention provides a capacitive sensor comprising a sensor conductor with a large guard conductor behind it, in which the sensitivity to distant objects is enhanced by minimising the area of conductive material forming the sensor conductor particularly in vertical strips representing the path of water over the sensor. Sensitivity to trickles of water such as from rain that flow over the sensor is thereby reduced.

Description

Capacitive sensor and how to make it {CAPACITIVE SENSOR AND METHOD OF PRODUCTION}

The present invention relates to a capacitive sensor for attaching to a vehicle for detecting the proximity of the vehicle to another object.

In recent years, sensors have been constructed in vehicles, particularly in the rear of vehicles, informing the driver of the presence of objects. In this way, when the vehicle is reversing, it is possible to approach the invisible objects (eg walls, pillars) while preventing collisions with them. In the general case, a series of audible alerts convey the approaching obstacle. These alarms sound closer as they get closer to the obstacle, causing the alarm to peak when the obstacle is at, for example, 35 cm away, signaling the driver to stop. The range in which this stop alert is generated corresponds to the stop distance.

Capacitive sensors have protective plates and sensor plates connected to the control unit. In use, the control unit supplies an AC signal to the sensor and the guard plate. Objects adjacent to the vehicle exhibit capacitance with respect to the ground. This capacitance is formed by two capacitances in series. That is, it is formed by the series coupling of the capacitance between the object and the sensor plate, and the capacitance between the object and the ground portion. The capacitance between the object and the ground is formed by the series coupling of the capacitance between the object, the surface on which the object and the vehicle is located, and the capacitance between the surface and the electrical ground of the vehicle. However, the capacitance between the object and the ground is very large compared to other capacitances and can be considered as a direct connection between the electrical ground and the surface of the vehicle sensor. The control unit measures this capacitance between the sensor plate and the ground. The control unit may be operated automatically when the reverse gear is connected, may be operated manually, or otherwise.

A particularly practical sensor structure for mounting between rear bumpers of a vehicle is shown in FIG. 1. The front face of the sensor body 12 is composed of sensor means or sensor plate 11 made of a conductive material. The sensor plate 110 includes a central portion with a uniform width and two ends with a wide width, which increase the sensitivity at the side of the vehicle due to the increase in the surface area. This is because, in the case of an object located on one side of the sensor plate 11, the sensitivity of the sensor at the side can be reduced, since the object can only be capacitively connected to this side of the sensor, while the sensor This is because the object directly in front of the plate will be capacitively coupled with the two sides of the sensor plate 11. This feature is particularly important in ensuring that the stopping distance is roughly uniform along the width of the vehicle GB 2,348,505. Provides enlarged ends for increased sensitivity at corners of the vehicle GB 2,376,075 discloses a calibrated arrangement for non-uniform sensor plates, in which case the area of the sensor per unit length is And changes in a selected portion of the document so as to provide the same sensitivity is increased, when using sensors that may be visible to provide an alternative design of a sensor that corresponds to the case useful.

A first guard plate (not shown) is provided on the opposite side of the sensor body 12 from the sensor plate 11. This first guard plate serves as a shield to reduce the sensitivity of the device to any object behind the sensor plate. The first guard plate and the sensor plate are insulated from each other by the substrate 12.

The second guard plate 13, shown in the form of a uniform strip, is located on the same side as the sensor plate 11. This second guard plate is also made of a conductive material and is disposed on the sensor plate in this example. However, it is possible to be placed anywhere below or on the sensor plate 11 depending on the vehicle shape. This second guard plate is disclosed in WO 02/084875.

The purpose of this second guard plate 13 is to protect the sensor plate 11 from interference. For example, protection is provided when water falls on a vehicle or a bumper, or when a person steps on a vehicle or a bumper. The second guard plate 13 has a signal corresponding to the signal applied to the sensor plate. In this aspect, the voltage supplied to the second guard plate has the same phase and frequency as the sensor plate, and the amplitude is preferably large. For example, it is preferably about 1.2 times larger than the amplitude supplied to the sensor plate.

The sensor 10 is generally provided inside the vehicle bumper, and the sensor plate 11 and the second guard plate 13 are provided at the outermost part of the vehicle in front of the sensor. The sensor portion with the first guard plate (not shown) is provided on the inner side closest to the vehicle.

The sensors of the structure shown in FIG. 1 are effective for shielding the sensor plate from rain or other effects. Other steps may be taken when processing signals from the sensor plate to mitigate the effects of water. However, reducing the ineffectiveness is important in design criteria, and improving these features will improve overall performance.

When designing a sensor with improved performance against near field interference, remember the capacitance formula below.

C = E ₀ E _τ A / L (1)

Where C is the capacitance between two objects, such as a drop of water and a sensor plate.

E ₀ is the permittivity of free space.

E _τ is the dielectric constant of the material. For air, E _τ = 1, and most plastics have E _τ = 2 to 3.5.

A is the facing conduction area of objects (eg sensor plates and water droplets).

L is the separation of the object (eg the distance between the droplet and the sensor plate).

As water droplets pass through a sensor plate placed in a nearby electric field, the water droplets capacitively couple with the sensor plate. This is an undesirable phenomenon and as these droplets pass, sharp spikes appear in the detection signal, which indicates a change in trajectory from the true detection signal. Therefore, in order to reduce the capacitance between the water drop and the sensor plate, it will be desirable to have a small sensor plate area when considering the formula (1).

However, in order to effectively detect the approach of an object in a far field, it is desirable that the capacitance between the object and the sensor be large. To implement this, when referring to formula (1), a large sensor plate area needs to be used. However, this adversely affects near field interference. This is because by increasing the sensor plate size, the effect of water droplets on the surface of the bumper close to the sensor plate is increased.

Equation (1) is an approximation for the ideal parallel plate capacitor. This formula works well when the area A of an object is much larger than the square of the distance between objects (L ² ). In other words, considering the interaction with objects close to the sensor, equation (1) can be used to estimate the capacitance between the objects and the sensor. However, considering the interaction with objects spaced far from the sensor, the above formula does not give an accurate capacitance value between the objects and the sensor. Because A is much smaller than L ² .

Therefore, in summary, the sensor plate area must be large for effective detection at a long distance. However, by increasing the sensor plate area, the effect of water passing through the sensor is also increased. This is not desirable. Conversely, in order to minimize the water effect, the plate size (and therefore capacitance) must be kept small. Therefore, two considerations (ie good overall sensitivity and minimal spikes due to water droplets) are at odds with each other.

The overall sensitivity of the system can be adjusted by selecting the resistance values in the amplification stage. However, in practical application situations such as parking assist devices, the remote range is limited by the sensitivity to uneven grounds that cause malfunctions. In this regard, as the system is designed to detect capacitance changes between the sensor and ground, the sensor needs to generate a high rate of capacitance change as it approaches the obstacle.

Overall, there is a need to provide a sensor having good sensitivity to remote objects within a predetermined range of the capacitive sensor. It is preferable that this remote object is an object to be detected, such as an object near the rear of the vehicle. This is related to reducing the effect of near-field interference by water passing through the sensor. This is particularly applicable to parking assist sensors attached to the rear of the vehicle, with the excellent sensitivity required for remote objects in the range of 50 mm to 2 meters, and typically low sensitivity to near field interference occurring within 5 mm of the sensor.

According to one aspect of the invention, the invention relates to a capacitive sensor, wherein the sensor is

A substrate, and

A long sensor plate formed on the surface of the substrate in a pattern of conductive material

Wherein the sensor plate includes a central portion and two outer portions arranged at both ends of the central portion along a longitudinal axis of the sensor plate,

In this case, the conductive material is arranged such that a plurality of virtual strips of similar width that are laterally arranged along the longitudinal axis of the sensor overlap the plurality of portions of the conductive material, wherein each virtual strip is formed of a substrate. Stretched across the width,

A capacitive sensor is provided wherein the total area of the conductive material overlapping each virtual strip is constant at the longitudinal center of the sensor plate.

The virtual strips may extend along the surface of the substrate in a first direction perpendicular to the longitudinal axis of the sensor plate.

The virtual strips may extend along a path in the expected direction of water flow on the surface of the sensor when used in a vehicle bumper. Thus, the sensor plate can be arranged such that the distribution of conductive material is constant in the strip even when the strips are not parallel. In other words, the direction that the strip takes between the sensors can vary along the length of the sensor so that various water flow directions can be taken into account for the length of the vehicle bumper. The arrangement of the sensor plates ensures uniformity of the material in each strip.

The outer portions may have different areas of conductive material in each strip compared to the central portion. This can provide the effect of having lobes as compared to systems of the prior art, for example to provide a result of increasing near and intermediate distance sensitivity around the corner of the vehicle. The center portion is preferably longer than each of the outer portions in the longitudinal direction. Thus, a uniform sensing area is maintained at the rear of the vehicle, and the water flowing through the surface is uniform. In this way, effects due to water flow can be easily eliminated. This is because, in the known art, the magnitude of this effect depends on the position along the sensor length.

By creating lines of conductive material with short vertical heights, reducing or minimizing the amount of conductive material that runs in the same direction as the near object is moving (e.g., vertical direction) will reduce the effect of water (usually vertical). It can be minimized. The capacitance between the stem and the sensor plate can be calculated by the parallel plate capacitance formula (1). Therefore, when the body of water moves vertically due to gravity, the value of A in Formula (1) can be made small by reducing the size of the conductive material through which the body of water flows. This means that the coupling capacitance between the sensor plate and the water stream is reduced, which means that the water effect on the sensor should be reduced.

By reducing the effective area of the sensor means, the remote sensitivity can be reduced. However, this reduction is less than the effect on near field sensitivity and can therefore be compensated for. Therefore, this aspect of the invention is capable of minimizing near field reductions without improperly harming the far range.

At a distance, the outer perimeter, defined by the conductive material, is more important than the actual area of the conductive material contained within this perimeter in determining capacitance and sensitivity. Therefore, the smaller the area enclosed by the outer circumference defined by the portions of the conductive material forming the sensor plate covers an adequately larger area, the smaller the effect of the area ratio of the area containing the conductive material on the sensor sensitivity is. do. The conductive material in the perimeter forming the sensor means is distributed in a regular pattern between the lengths of these regions. Moreover, by means of the "appropriately large area" of the sensor means, the area of the same circumference as in the case of existing sensors is taken into account, despite the reduced use of conductive material therein.

The terms "horizontal" and "vertical" should be considered as relating to long sensors located on the bumper in the vehicle rear. Therefore, the horizontal direction should be regarded as the direction along the length of the vehicle bumper and the vertical direction as the gravity direction.

Near-field interference is generally due to the flow of water on the sensor (or the insulating surface of the sensor). Water can be judged as rain, condensed water due to weather or local conditions, or water dissolved in ice.

According to another aspect of the present invention, there is provided a method for detecting the presence of an object proximate to a sensor in a raining situation, comprising providing a capacitive sensor as described above.

According to a further aspect of the present invention, the use of a capacitive sensor is provided in a vehicle bumper to mitigate the sensitivity to water flowing over the vehicle bumper. The vehicle bumper includes an outer skin, which is provided with a capacitive sensor on the inner surface of the outer skin. The capacitive sensor

A substrate, and

A long sensor plate formed on the surface of the substrate in a pattern of conductive material

Wherein each of the virtual strips extending along the surface of the substrate in a first direction perpendicular to the longitudinal axis of the sensor plate comprises a plurality of portions of conductive material, wherein the plurality of portions are conductive materials. Spaced apart from each other by one or more regions.

According to a further aspect of the present invention, there is provided a capacitive sensor comprising a substrate and an elongated sensor plate formed in a pattern of a conductive material on the surface of the substrate. The sensor plate then comprises a plurality of parallel strips spaced apart from one another, which strips are arranged along the longitudinal axis of the sensor.

According to a further aspect of the invention there is provided a capacitive sensor comprising a substrate and an elongated sensor plate formed on the surface of the substrate in a pattern of conductive material, wherein the sensor plate is along a longitudinal axis of the sensor. And a strip of conductive material provided around the outer perimeter of the elongate area of the substrate that extends.

According to a further aspect of the invention there is provided a capacitive sensor comprising a substrate and an elongated sensor plate formed on the surface of the substrate in a pattern of conductive material, wherein the sensor plate is arranged along the longitudinal axis of the sensor. V-shaped interconnect shaped strips.

1 is a view of a sensor and guard plate arrangement according to the known art.

2 is a diagram of capacitance associated with a capacitive parking assist sensor mounted behind a rear bumper of a vehicle.

3 is a cross sectional view of a rear bumper of a vehicle with capacitance and capacitive sensors associated with droplets flowing along the bumper;

FIG. 4 is a graph of typical output results for the sensors shown in FIGS. 1, 6, 8, 9 when the vehicle slowly reverses toward a large obstacle (eg, another vehicle) for 160 seconds along the road. As the obstacle approaches, the voltage output from the sensor increases. Before reaching the obstacle, there is a small fluctuation in the sensor output due to the ups and downs of the road.

5 is a graph of the output sensor response when water droplets fall on the bumper in the case of the known technology sensor of FIG.

6 is a diagram of a sensor arrangement in accordance with a first embodiment of the present invention.

7 is a graph of output sensor response in the sensor arrangement according to the first embodiment of the present invention.

8 is a diagram of a sensor arrangement according to a further embodiment of the invention.

9 is a diagram of a sensor arrangement according to another embodiment of the invention.

10 is a cross-sectional view of the sensor of FIG. 9 with respect to line AB.

FIG. 11 is a view of the coupling occurring between the water droplets and the sensor plate of the sensor of FIG. 9; FIG.

FIG. 12 is a graph comparing the area of the sensor plates for the solid, 6 (5-bar) and 9 (wire) sensors, charting the relative sensitivity at a distance.

FIG. 13 is a graph comparing the area of the sensor plates for the sensors of FIGS. 1, 6, 9, charting the relative sensitivity to ratio.

To illustrate the theory hidden in aspects of the present invention, FIG. 2 shows the capacitance when a vehicle with a capacitive parking assist sensor 1 mounted behind a rear plastic bumper of the vehicle retracts towards an obstacle 3. do. The guard plate 2 is mounted between this sensor 1 and the vehicle body.

In the absence of obstacles, the capacitance between the sensor and ground consists of a number of parallel capacitances:

Ca is the capacitance between the body and the sensor on the guard.

Cb is the capacitance between the body and the sensor under the guard.

Cc is the capacitance between the sensor and ground.

The body is capacitively coupled to the ground (ground) by the capacitance Cz, and the capacitance between the sensor and the ground actually corresponds to the series coupling of Cc and Cz. Since Cz is much larger than Cc, Cz can generally be ignored. Therefore, it is preferable to consider that the vehicle body and the ground are directly connected, and reference to the ground portion herein should be regarded as related to both the body ground portion and the ground ground portion.

There is also a capacitance Cd (not shown) between the sensor and the vehicle body beyond the end of the sensor, and there is also a small capacitance between the sensor and the vehicle body through the guard plate. The small capacitance mentioned is due to the guard signal, and because of the nonlinearity of the guard amplifier, the guard signal does not completely follow the signal of the sensor.

The total capacitance between the sensor and the body corresponds to the sum of all these capacitances arranged in parallel.

Co = Ca + Cb + Cc + Cd (2)

All these capacitances depend on the area of the sensor plate. Therefore, as the area of the sensor plate increases, all capacitances increase.

When the vehicle approaches the obstacle 3, the vehicle senses additional capacitance (Cz and Cp of the serial connection). As mentioned above, we can generally ignore Cz. The output of the sensor change is approximately proportional to the capacitance increase.

V = K * (Cp + Co) / Co (3)

Where V is the output voltage (called sensitivity).

K is a proportional constant.

Cp is the additional capacitance caused by approaching an obstacle. Co is the background capacitance between the sensor and ground as in equation (2).

Capacitance Cp also increases with sensor area. If the capacitance of the various components (Ca, Cb, Cc, Cd, Cp) increases linearly with the sensor plate area, the change in voltage V will be independent of the actual area of the sensor plate.

This theory was tested with respect to FIG. 12. At this time, it is possible to compare the remote sensitivity results of a plurality of different sensor plates having conductive materials of different areas mounted on the same guard. This test was performed with three sensor arrays. The first arrangement was a single narrow strip (or wire) running between the widths of the bumpers. The second arrangement was a sensor similar to the sensor shown in FIG. 6 with five narrow strips stacked on top of each other. The third sensor arrangement was similar to the prior art arrangement, with a wide strip extending between the bumper widths. The third array of sensors had a similar perimeter to the second array, but the amount of conductive material in this area was much higher. 12 shows that the change in output voltage increases with the area of the conductive material.

Next, consider the near field effect. See FIG. 3. Water droplets 4 flow down the bumper 5. 3 is a cross-sectional view of the bumper 5 mounted on the metal vehicle body 3 with the sensor 1 and the guard 2. The upper part of the water drop on the guard forms a capacitive coupling with the body (Cx). If the water droplets run long enough, the coupling to the car body may be under the guard. Such a bond to the guard is disclosed in WO 02/084875.

As the water droplets pass through the sensor means 1, the water droplets form a capacitive coupling with the sensor means 1, the capacitance of which is represented by Cy. As water droplets pass through the sensor means, the capacitance to the vehicle body (ground part) increases by the series coupling of Cx and Cy.

Water droplets can be thought of as the short length of the conductor flowing down the bumper skin. Pure water is not a good conductor, but given the large impedance value of the capacitance measurement circuit, the electrical resistance of water in water droplets is relatively low and can therefore be ignored.

If the sensor is mounted directly under the bumper skin, the water droplets will pass very close to the bumper. The surfaces of the vehicle bumpers are typically made of polypropylene about 3 mm thick and have a dielectric constant of approximately three. Due to the proximity of the droplet to the sensor means, the capacitive coupling Cy between the droplet and the sensor means can be calculated using the parallel plate capacitance formula (1). The capacitance Cy thus depends on the opposing area between the sensor means and the length of the conductor representing the water drop. In other words, the effective area is the overlapping area between the water drop and the conductive portion of the sensor plate.

Therefore, in order to minimize Cy, it is necessary to minimize the contact area between the sensor and the water droplets. Since it is common for water droplets to take a vertical path, Cy can be minimized by arranging the sensors with small cross-sections of conductive material in vertical strips up and down on the surface of the bumper.

As shown below, the effect of changing the shape of the sensor plate upon the detection of water droplets is significant. FIG. 13 shows this change for the three sensors used in the example shown in FIG. 12.

Combining this near-field interference effect with remote object sensitivity, one embodiment of the invention provides a laterally long and vertically short sensor means. In other words, the theory suggests that since the capacitance Co between the sensor and the ground is related to the area of the sensor plate, its absolute value is not important for remote detection. Considering distant objects, the sensitivity is more relevant to the total area contained within the perimeter of the sensor exposed to obstacles and less relevant to its own area of the sensor plate.

Furthermore, to minimize Cy, it is necessary to minimize the area of conductive material that overlaps between the sensor and the droplets. This can be achieved by arranging the sensor means having a small cross section in the direction in which non-interference generally flows (generally perpendicular to the length, ie vertical direction). In an ideal case, the cross section of the sensor means is small in the direction perpendicular to the vertical, in order to take into account the water passing through the sensor in a direction other than vertical. This occurs when air or wind pressure is applied to the rain that flows down the bumper of the vehicle and to the swirling airflow behind the vehicle. This airflow causes the water to deviate from its natural vertical path, resulting in an oblique flow of the resulting flow.

6, a capacitive sensor 20 according to a first embodiment of the present invention is shown. The sensor 20 is formed on the substrate 21, which is preferably a plastic film. A first guard plate (not shown) is formed on the back side of the sensor body. Alternatively, the first guard plate may be formed on the front of the sensor body. This simplifies manufacturing and assumes a case of being electrically insulated from the sensor means 24.

In this embodiment the sensor means 24 is formed of a plurality of conductive strips. In FIG. 6, five conductive strips are shown. To facilitate sensor plate formation, it is preferred, but not necessarily, that the conductive strips be arranged in parallel line form. For example, there may be more than one line, and each line may be curved or zigzag. It is also desirable for the conductive strips to be as narrow as possible without changing mechanical strength or electrical resistance. Therefore, the width depends on the construction method selected, but is preferably 1 mm or less. Furthermore, when two or more lines are used, the separation distance is preferably 5 mm or more.

In the embodiment of FIG. 6, the sensor plate has lobes towards each end of the strip. In this embodiment, the lobes are formed by providing one or more additional strips of reduced length at each end of the sensor strip. In Fig. 6, one lobe strip 26a, 26b is disposed at each end of the sensor plate, each strip having a length corresponding to the length of the desired lobe. The lobe strips 26a, 26b need not be arranged immediately adjacent the end of the sensor plate. For example, the lobe strips may be spaced apart toward the center. The lobes provide increased sensitivity at the corner of the vehicle, providing excellent sensitivity for objects not directly behind the vehicle and providing uniform sensitivity across the entire width of the vehicle. The principle of providing such a lobe is well known in the art.

The lines of the conductive strip (thought to include additional lobe strips) are formed by a first conductive interconnect 25a formed at one end of the strip line and a second conductive interconnect formed at the other end of the strip line. 25b) are electrically connected to each other. As shown in FIG. 6, conductive interconnects are disposed diagonally across the line of conductive strips, extending from the corner end of the lobe strip to the upper conductive strip. The conductive interconnects are electrically connected to the upper conductive strip at a position corresponding to the length of the lobe strip. The horizontal flat lines connect with the diagonal strips, minimizing the area exposed to the droplets as they flow. When these connections are vertical, water droplets flowing along the surface of the bumper strongly bond these connections and cause misreading. By diagonalizing the connection in this way, any droplets will pass through only a small portion of the connection. Moreover, this additional material can be compensated for by thinning the parallel strips to which it is connected.

Other arrangements for connecting the lines together are possible. For example, they can be connected under the sensor or even at a remote connection point.

In this embodiment, the second guard plate 22 is formed on the front surface of the substrate. This front face is the outermost part of the vehicle in which the sensor 20 is located, as in the case of FIG. The second guard plate may have lobes 23a and 23b towards the ends of the plate. Lobes of the second guard plate make it possible to mitigate or prevent output spikes caused by drips (i.e., meaning 'drip'). This offsets the area increase that the sensor lobes present to the droplets. In this respect, the larger the area of the lobes, the greater the adverse effect of the spikes, as the contribution to the effective area of the conductive lobe in the case of water droplets flowing along the lobe is greater in the diagonal line than in the vertical downward. This can be offset by increasing the width of the second guard plate near the lobe.

Overall, the purpose of this design is to minimize the capacitance (ie, area) between the second guard plate and the droplets as the droplets flow down the front of the bumper. For example, comparing this design to the known art arrangement of FIG. 1, water droplets flowing vertically down the central region of the sensor plate of FIG. 6 are the sensor area corresponding to the product of the width of the droplet and the width of each line of the sensor. Combine only with There is no coupling with the area of space between the lines. However, in the arrangement of FIG. 1, there is no margin space, so coupling occurs over the full width of the sensor plate. Thus, the droplets will form a larger capacitor with the sensor, which in turn will have a greater effect.

In this embodiment the area within the outer boundaries defined by the sensor plate 24 and the area of the conductive surface are selected to provide the desired range by the sensor to indicate that the vehicle is close enough to the object to stop.

As described above, the capacitance does not increase with the sensor plate area, and in the case of a remote object, the relationship between the sensor area and the sensitivity is nonlinear. For example, for a 1-meter-long thin strip sensor plate, when the object is 20 cm away, the capacitance ratio between the strip that is 1 mm wide and the strip that is 2 mm wide is approximately 1.5. Thus, doubling the strip size results in a 1.5 times increase in capacitance (considering the standard capacitance formula (1), the capacitance would have to be doubled for parallel plate capacitors). Similarly, halving the strip size, the capacitance reduction is only one-third (capacitance must be reduced by half in formula (1)).

Therefore, if the sensor plate is formed with five lines of 1 mm thickness at 5 mm intervals rather than one line of 25 mm thickness (in this case, the two overall widths are the same), the distance sensitivity is only slightly reduced. As can be seen in FIG. 12, the sensor of FIG. 6 will have about one fifth of the area of the sensor of FIG. 1. However, with about one third of the sensitivity to rain, you have 90% of the remote sensitivity.

An additional advantage of the conductive sensor type shown in FIG. 6 is that the capacitance between the sensor plate 24 and the rear guard plate (not shown) is reduced. If the capacitance is large, it is preferable that the capacitance is small because a high load is placed on the amplifier driving the guard plate. As a result, it is possible to reduce the thickness of the substrate 20 without exceeding the maximum allowable capacitance between the sensor plate and the rear guard plate. As a description of this, the sensor of FIG. 1 generally uses a 250 micron thick film, while the sensor of FIG. 6 uses a 125 micron thick film. Reducing the substrate thickness results in less weight and lower costs.

8 shows an alternative form of sensor plate 50 according to a second embodiment of the invention. The sensor plate 50 includes a substrate 52 and a first guard plate (not shown) on the rear surface. On the sensor plate 51, a second guard plate 53 is also arranged in front of the sensor. In this embodiment, the sensor plate 51 takes the form of an outline. The contours are completely interconnected and have two lobes 54a and 54b formed towards both ends of the sensor plate.

In testing, it can be seen that this contour sensor has a sensitivity range similar to that of the known art sensor of FIG. 1 over long distances. It has also been found to have improved water performance (ie, reduced sensitivity to rain, etc.) at close range.

Another alternative form of sensor is shown in FIG. 9. 10 is a cross-sectional view of the embodiment of FIG. 9 (cut in line AB). In this embodiment, the main guard plate 61 is formed on the substrate 62. The guard plate 61 is made of a conductive material such as a metal foil, and the substrate is preferably a plastic film. A second guard plate 63, such as a metal foil strip, is arranged on the main guard plate 61, but is insulated from the main guard plate 61 via the insulation means 64. Insulation means is preferably another plastic film. The plastic film / second guard plate combination is attached to the surface of the main guard plate using the adhesive 65.

In this embodiment of the invention, the conductive material lies in the form of a series of vertically formed V-type interconnects. The conductive material is a 0.2 mm diameter copper wire, which may be partially flat. This copper wire has an enamel coating 67. This coating serves to insulate the copper wire from the main guard plate 61. The enameled copper wire is fixed to the main guard plate using adhesive 65. A protective film 68 is placed over the sensor and fixed by lamination (preferably).

As in the embodiment of Figure 6, this sensor plate requires less conductive material to form the sensor plate. By forming the sensor means using less conductive material, the thickness of the substrate 61 can be reduced, thereby lowering cost and weight. Moreover, the capacitance between the sensor means 66 and the main guard plate 61 is preferably reduced in terms of reduced sensor means 66 area.

Some comparative examples will be provided to illustrate the advantages of the result of the formation of the sensor plate according to this embodiment.

First, a water performance test was performed with the sensors of FIGS. 1 and 6 attached to the vehicle bumper. In this test, the vehicle bumper was 3 mm thick and drenched in water from a titrator at a rate of 0.03 ml per second. In this way, rain in nature was simulated, and water was periodically supplied to the bumper before water droplets flowed down the bumper.

5 and 7 show the resulting sensor output of the sensors of FIGS. 1 and 6, respectively. Each droplet is coupled to the sensor because of its proximity, causing spikes upon the combination of the droplet and the sensor. It is foreseen that the second guard conductor in each of the tested sensors makes many of these spikes negative.

By comparing FIG. 5 with FIG. 7, it can be seen that the sensor according to FIG. 6 generates spikes of small amplitude. Compared to the sensor of FIG. 1, the influence of water on the sensor of FIG. 6 is smaller. This is because formula (1) applies to near-field water interference. That is, because the water is located very close to the sensor (eg 3 mm distance), the parallel plate capacitance formula is applied at close range for the coupling between the droplet and the sensor.

Referring to Fig. 13, an alternative graph is shown, which compares the sensitivity of the Figs. 1, 6, 9 sensors at close range with respect to the cross-sectional area. To obtain this data, water from the titrator wetted the vehicle bumper and each sensor was attached to the vehicle bumper. Each drop produced spikes at the sensor output of variable size, and this graph shows the average size of spikes recorded at 4 minute intervals. The sensor in FIG. 1 (which means “sol lead sensor means”, ie, in the form of a unit rather than several strips) has a maximum average spike sizes of 609 units. The average cross-sectional conduction area of the sensor of Figure 1 is also the maximum, on the order of 40000 mm ² . It can be seen from this graph that 1024 units correspond to a 5-volt output from an A / D converter connected to the sensor output. In addition, the average spike size was calculated using the area of the graph of the A / D output of the spikes over time. The A / D converter measured the output every 20ms.

The sensor of FIG. 6 has sensor means formed of conductive material consisting of five bars, with an average spike size of 211 levels. This is less. Likewise, the average cross-sectional conduction area of the FIG. 6 sensor is also reduced and is approximately 8850 mm ² .

Finally, the sensor of FIG. 9 has sensor means formed of wires in a vertically formed V-shaped arrangement, with a minimum average water spike size of about 147. The average cross-sectional conduction area of this sensor is also minimal, at 1540 mm ² .

Thus, first considering the sensor of FIG. 6 compared to the sensor of FIG. 1, the sensor of FIG. 6 is 78% in terms of its average cross-sectional conduction area, and this reduction corresponds to a 65% performance improvement due to the near water effect. do.

The sensor of FIG. 9 is 96% smaller than the sensor of FIG. 1, and this reduction corresponds to a 76% performance improvement over near field interference. Thus, the desired near field sensitivity depends on the area of the conductive material in any vertical cross-sectional area of the sensor means.

Next, consider FIG. 12. FIG. 12 graphically depicts the far field performance of FIGS. 1, 6 and 9, which compare this performance to the average cross-sectional conduction area. This remote sensitivity was measured by approaching a 25mm diameter steel pole vertically grounded from 3 meters towards the vehicle. As the vehicle approached the steel pole, a change was made in the sensor output voltage. When this movement produced a 1 volt change in sensor output, sensitivity was measured with the pole's distance from the vehicle.

The sensor of FIG. 1 with solid sensor means has an optimum far field sensitivity, at a distance of 310 mm. The five-bar sensor of FIG. 6 has the next highest intensity, with a distance of 276 mm. The wire sensor of FIG. 9 has the highest sensitivity at 262 mm.

Thus, the sensor of FIG. 6 has an 11% reduction in remote sensitivity compared to the FIG. 1 sensor of the prior art. Remember that near-field improvement is 65%.

The sensor of FIG. 9 shows a 15% reduction in remote sensitivity. At close range, 76% improvement is achieved.

Thus, the reduction in far field sensitivity is not as remarkable as the improvement in near field interference due to rain. Far-field sensitivity increases with sensor area, but these changes are not significant and are nonlinear. For example, a 30-fold increase in sensor area only increases the sensitivity of the sensor by 20%.

The rough reduction of the sensitivity of the sensors of FIGS. 6 and 9 can be corrected by increasing the amplification of the electronic device.

In particular, in the embodiment of Figure 9, the near-field sensitivity improvement is seen because it minimizes the area that engages the water droplets running down the vehicle bumper vertically. This is shown in FIG. 11 where water droplets 81 pass across the surface of the V-shaped sensor means 82 formed vertically of the FIG. 9 sensor. Due to the shape of the sensor means 82, the area 83 at which the water droplets engage with the sensor is reduced, and therefore the interference (taken in the form of voltage spikes) caused by this water droplet is also reduced.

The figure shows that even if the body of water 81 falls in a direction other than vertically between the sensor means 82, the body of water will still engage with a small portion of the conductive sensor 82. The angle of the zigzag can be adjusted to compensate for the expected rain angle. For example, in a given environment, if a non-flow is expected to deviate significantly from the vertical, the zigzag will be flattened to ensure that the stream of water flows only diagonally along the line.

Thus, as a whole, by selecting the area of the sensor means having an appropriate size to produce the desired far-field sensitivity, or by selecting the area of the sensor means having an appropriate size to generate the sensitivity within the tolerance of the desired far-field sensitivity. And by distributing the conductive material over this area to form the sensor means, the desired near field sensitivity can also be obtained based on the distribution of the conductive material. For example, when the cross-sectional area of the conductive material is minimized, near-field sensitivity is also minimized. That is, the sensor is minimally affected by the near-field interference effect. Embodiments of the present invention thus suggest a compromise between the far and near performance of a sensor.

Modifications and additions to the invention are possible within the spirit of the generic invention.

For example, although the form of the sensor conductor is considered to be the only form of sensor conductor preferred, other forms and structures are possible. For example, to deal with the adverse effects on sensor sensitivity caused by metal objects attached to the bumper, such as plates, the vertical width of the sensor conductors can be made smaller than the metal object area. Alternatively, the sensor plate can be formed to have a central portion of uniform width and two ends with gradually increasing width.

The sensors of the present invention are mounted to the rear of the vehicle to assist the driver's driving when reversing. However, this sensor may also be suitable for front or side mounting in order to prevent collisions with invisible low position objects under the bonnet. In addition, when the vehicle is moving forward or backward, at the same time there is a risk that the side wing portions will collide with the object if the vehicle rotates.

The sensor of the present invention is designed assuming a use case when the outer cover of the sensor becomes wet and when the sensor needs to operate in such a condition. Also included herein are sensors for detecting whether a vehicle door, bonnet, tailgate, or the like may collide with an obstacle during opening and closing. This is particularly important when they are driven by a motor. In other cases, capacitive sensors can be used to monitor the types of doors that can be opened and closed by sliding panels (eg vehicle windows, sunroofs). For example, a system designed to inspect obstacles such as a person's arm when closing a vehicle window or sunroof. An additional application would be a sensor system that detects obstacles when closing the roof of a convertible vehicle (ie, a vehicle that can fully open and close the roof). All these systems should work even in the rain.

Moreover, the techniques mentioned in connection with creating the sensor of FIG. 9 can likewise be used to fabricate sensors of other embodiments of the invention.

The capacitive sensors according to the invention can be mounted on any opening and closing, so that the sensor can be used to detect the presence of an object that can collide by the opening or closing of the opening or closing. The opening and closing portion may be a vehicle door, tailgate, or bonnet. Alternatively, this opening and closing may be a power sliding window, a power sunroof, or a power opening / closing hood (of a convertible vehicle).

Claims (20)

In the capacitive sensor, the sensor, A substrate, and A long sensor plate formed on the surface of the substrate in a pattern of conductive material Wherein the sensor plate includes a central portion and two outer portions arranged at both ends of the central portion along a longitudinal axis of the sensor plate, In this case, the conductive material is arranged such that a plurality of virtual strips of similar width that are laterally arranged along the longitudinal axis of the sensor overlap the plurality of portions of the conductive material, wherein each virtual strip is formed of a substrate. Stretched across the width, Wherein the total area of the conductive material overlapping each of the virtual strips is constant at the longitudinal center of the sensor plate. The capacitive sensor of claim 1, wherein the virtual strips extend along the surface of the substrate in a first direction perpendicular to the longitudinal axis of the sensor plate. The capacitive sensor of claim 1, wherein the virtual strips extend along the surface of the substrate in a direction corresponding to a desired direction of water flow on the surface of the sensor. The capacitive sensor according to any one of claims 1 to 3, wherein the conductive material is formed of one or more lines extending along the longitudinal axis of the sensor plate. 5. The capacitive sensor of claim 4, wherein the lines of conductive material are straight and parallel to each other. 5. The capacitive sensor of claim 4, wherein the lines of conductive material are inclined or curved along the length direction. 7. The capacitive sensor of claim 6, wherein the lines of conductive material take the form of a V-type interconnect. 8. The capacitive sensor of claim 7, wherein a line is bent at each V point of the V-type interconnect. 9. The capacitive sensor according to any one of claims 1 to 8, wherein the conductive material is formed of a wire attached to the substrate surface. 10. The capacitive sensor according to any one of claims 1 to 9, wherein the conductive material is formed of one or more lines having a width in the range of 0.2 to 2 mm. The capacitive sensor according to any one of claims 1 to 10, wherein the central portion is longer in the longitudinal direction than each outer couple. 12. A vehicle bumper comprising the capacitive sensor according to claim 1. A proximity sensor comprising a capacitive sensor according to any one of claims 1 to 11, characterized in that it is mounted on a vehicle to detect the presence of objects adjacent to the vehicle as the vehicle and objects approach each other. Proximity sensor. A method for detecting the presence of an object adjacent to a sensor in the presence of rain, The method includes providing a capacitive sensor, the sensor comprising: A substrate, and A long sensor plate formed on the surface of the substrate in a pattern of conductive material Wherein the sensor plate includes a central portion and two outer portions arranged at both ends of the central portion along a longitudinal axis of the sensor plate, At this time, each of the virtual strips extending along the surface of the substrate in a first direction perpendicular to the longitudinal axis of the sensor plate overlaps each of the plurality of conductive materials, Wherein the total area of the conductive material overlapping each of the virtual strips is constant at the longitudinal center of the sensor plate. A capacitive sensor mounted to a vehicle bumper to mitigate sensitivity to water flowing down a vehicle bumper, the bumper including an outer skin, the capacitive sensor being disposed on an inner surface of the outer skin, and the capacitive sensor The sensor is A substrate, and A long sensor plate formed on the surface of the substrate in a pattern of conductive material Wherein the virtual strips extending along the surface of the substrate in a first direction perpendicular to the longitudinal axis of the sensor plate overlap with respective portions of the conductive material, each portion of the conductive material being conductive A capacitive sensor mounted to a vehicle bumper, characterized in that they are spaced apart from each other by one or more areas free of material. In the capacitive sensor, the sensor, A substrate, and A long sensor plate formed on the surface of the substrate in a pattern of conductive material Wherein the sensor plate comprises a plurality of parallel strips spaced apart from each other, each strip arranged along a longitudinal axis of the sensor. In the capacitive sensor, the sensor, A substrate, and A long sensor plate formed on the surface of the substrate in a pattern of conductive material Wherein the sensor plate comprises a strip of conductive material provided around an outer perimeter of the elongated area of the substrate extending along the longitudinal axis of the sensor. In the capacitive sensor, the sensor, A substrate, and A long sensor plate formed on the surface of the substrate in a pattern of conductive material Wherein the sensor plate comprises V-shaped interconnect shaped strips arranged along the longitudinal axis of the sensor. A method as described with reference to FIGS. 2 to 10. Apparatus characterized in that described with reference to FIGS.

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