WO2009048910A2

WO2009048910A2 - Sensor assembly comprising a capacitive proximity sensor

Info

Publication number: WO2009048910A2
Application number: PCT/US2008/079142
Authority: WO
Inventors: Dyfrig E. Clement; David Cook; Malcolm F. Douglas; Robert G. Every; Martyn Hagedorn; Helen G. James; Gareth M. Jones; Frédéric JOUVET; Richard A. Loyd; Nigel W. S. Matchett; Philip A. Rowlands
Original assignee: 3M Innovative Properties Company
Priority date: 2007-10-10
Filing date: 2008-10-08
Publication date: 2009-04-16
Also published as: KR20100085969A; GB0719807D0; WO2009048910A3; JP2011501350A; EP2205466A2; CN101821133A

Abstract

A sensor assembly comprises a capacitive proximity sensor (1) mounted to a shaped surface of a body, such as the internal surface (10) of a vehicle bumper (11), to sense the presence of external objects. The sensor comprises a dielectric film substrate (2) having front and rear major surfaces that, in use, face respectively outwards and inwards of the body, a sensor conductor (6) on the front major surface, and a guard conductor (8) on the rear major surface to provide an electrical shield for the sensor conductor. The surface (10) to which the sensor (1) is mounted is one that does not provide a substantially flat area for direct attachment of the sensor, at least in the sensor conductor region, and, with a view to ensuring the correct functioning of the sensor, the sensor mounting is designed to inhibit the ingress and retention of water/dirt between the sensor and the shaped surface, and to enable a major part of the sensor substrate to be maintained in a substantially flat condition at least in the sensor conductor region.

Description

SENSOR ASSEMBLY COMPRISING A CAPACITIVE PROXIMITY SENSOR

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to Great Britain Patent Application No. 0719807.0, filed October 10, 2007, the disclosure of which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

[0002] The present invention relates to the mounting of a capacitive proximity sensor in a body to detect the presence of external objects. The invention relates more especially (but not exclusively) to the mounting of a capacitive proximity sensor in a vehicle, especially a vehicle bumper.

BACKGROUND

[0003] Proximity sensors have been used in various industrial applications for locating the presence of materials and for avoiding collisions with articles. In one field of application, proximity sensors have been fitted to the rear side and/or bumpers of vehicles so that, when a vehicle is reversed, a warning signal is provided if it approaches an object so that a collision can be safely avoided while still allowing the driver to position the vehicle conveniently close to the object.

[0004] WO 01/08925 (AB Automotive Electronics Ltd.) describes a capacitive proximity sensor for a vehicle, which consists of two strips of metal, or other conductive material, insulated from each other and provided on the inside of the bumper of a vehicle. One strip, which faces outwardly from the vehicle, is referred to as the sensor plate and the other strip, which faces inwardly towards the vehicle, is called the guard plate. Both plates are connected to a control unit. The control unit monitors the change that occurs in the capacitance between the sensor plate and (electrical) ground as the vehicle approaches an external object and provides an indication to the driver of the distance between the sensor plate (and, hence, the vehicle) and the object.

[0005] GB-A-2 400 666 (also of AB Automotive Electronics Ltd.) mentions the manufacture of a capacitive proximity sensor of the type described in WO 01/08925 by screen-printing the sensor and guard plates with conductive ink onto opposite sides of a plastic film substrate, or by forming the sensor and guard plates from aluminium foil that is laminated to the plastic film substrate. GB-A-2 400 666 further describes the use of a retention system for retaining the sensor in a vehicle bumper without the need for glues.

SUMMARY

[0006] The present invention is concerned with capacitive proximity sensors of the type in which a sensor conductor and a guard conductor are arranged on opposite faces of a dielectric film substrate. Sensors of that type offer the advantage that they can be manufactured in a cost-effective manner in the form of a flat sheet that is comparatively easy to store and to handle. They can be applied comparatively easily to flat supporting surfaces and, because they are flexible, to certain non-planar surfaces also (most typically, these will be surfaces that have only one axis of curvature but they could be surfaces that also have limited curvature about a second axis). Care is required, however, when such a sensor is being applied to a supporting surface that has a more complex shape (such as the inwardly-curved (i.e., concavely curved) internal surface of some vehicle bumpers) to ensure, as far as possible, that the formation of folds and creases in the sensor substrate, which could interfere with the correct functioning and durability of the sensor, is avoided. Folds and creases in the sensor substrate could permit dirt and/or water to penetrate, and be retained, between the sensor and the supporting surface. The build-up of water, particularly between the sensor conductor and the supporting surface, may affect the capacitive function of the sensor while the build-up of dirt anywhere between the sensor and the supporting surface may result in the surface of the sensor being abraded, causing the sensor to malfunction. There is an additional risk, when water is retained between the sensor and the supporting surface, that the sensor will be damaged as a result of the water freezing.

[0007] One way of reducing the number of folds and creases that form in the sensor substrate when it is being applied to a shaped supporting surface is to make tapered cuts at appropriate points in the substrate to make it easier to adapt the substrate to the shape of the supporting surface. This increases the complexity of the attachment process, since the shape and location of the cuts must be carefully selected having regard to the shape of the supporting surface to achieve the desired result and to avoid introducing too many points of weakness into the sensor substrate.

[0008] The present invention is concerned with enabling such problems to be avoided while providing a system for attaching a capacitive proximity sensor to a supporting surface that is sufficiently robust to withstand the forces and environmental conditions to which it may be subjected when in use. In the specific case in which the sensor is to be attached to the rear side of a vehicle or to the vehicle bumper, the attachment system should be able to withstand the forces caused by normal use of the vehicle as well as environmental conditions which might include variations in temperature, and exposure to dirt and/or water and/or oil.

[0009] The present invention concerns a sensor assembly comprising a capacitive proximity sensor mounted to a surface of a body to sense the presence of external objects. The sensor comprises a dielectric film substrate having front and rear major surfaces that, in use, face respectively outwards and inwards of the body, a sensor conductor on the front major surface, and a guard conductor on the rear major surface to provide an electrical shield for the sensor conductor. The invention further concerns the situation in which the surface of the body to which the sensor is mounted does not provide a substantially flat area for direct attachment thereto of the sensor, at least in the sensor conductor region. According to the invention, the sensor is provided with a mounting to the surface that inhibits the ingress and retention of water/dirt between the sensor and the said surface (at least during normal use) and maintains the sensor in a substantially flat condition, at least in the sensor conductor region.

[0010] In the context of the present disclosure and as applied to the said surface of the body, the term "substantially flat" includes the case in which the surface is non-planar but only to an extent that still permits the sensor to be attached the surface without being folded and/or creased at least in the sensor conductor region. Thus, as applied to the surface, "substantially flat" may include surfaces that have a single axis of curvature and may even include some surfaces that also have limited curvature about a second axis. As applied to the sensor, the term "substantially flat" includes the case in which the sensor is non-planar but only to the extent that it is not folded and/or creased at least in the sensor conductor region. [0011] Generally, the sensor is mounted to a supporting surface that does not allow direct attachment without the formation of folds and/or creases in the sensor at least in the sensor conductor region. Nevertheless, the sensor is maintained in a substantially flat condition, at least in the sensor conductor region, and the ingress and retention of water/dirt between the sensor and the supporting surface is inhibited (at least during normal use). In some cases, in normal use, it may be possible to permit the passage of water (e.g. rainwater) between the sensor and the supporting surface without the performance of the sensor being affected. That may be the case, for example, when the sensor is provided with a superguard conductor as described in GB-A- 2,374,422. [0012] In embodiments, the said surface of the body may be an internal surface and/or may be inwardly-curved (i.e. concavely-curved). The surface may, for example, be the inwardly-curved internal surface of the bumper of a vehicle, in which case the use of the invention increases the range of vehicle bumpers in which the capacitive proximity sensor can be conveniently employed. In some embodiments, the sensor can readily be employed in vehicle bumpers that curve about two axes (e.g., a vertical and a horizontal axis). In other words, the sensor can be employed in bumpers that have compound curvature, as well as those that are substantially flat or curve about a single axis only. Advantageously, when the sensor further comprises a superguard conductor on the front major surface of the substrate, the sensor mounting is such that the superguard conductor is located comparatively close to the inwardly-curved internal surface of the bumper. The sensor assembly may be provided in a vehicle bumper after manufacture, but may also be incorporated during the bumper manufacturing process.

[0013] The present invention further provides a capacitive proximity sensor for mounting to a surface of a body to sense the presence of external objects, the sensor comprising a dielectric film substrate having front and rear major surfaces that, in use, face respectively outwards and inwards of the body, a sensor conductor on the front major surface, and a guard conductor on the rear major surface to provide an electrical shield for the sensor conductor; wherein the sensor substrate is pre-formed with bending lines along which the sensor can be bent to shape it for attachment to the said surface of the body. A sensor in accordance with this aspect of the invention can be mounted, for example, in a vehicle bumper using mechanical attachment means so that it closely follows the shape of the bumper. [0014] The invention further provides a method of making a vehicle bumper assembly comprising the steps of: providing a capacitive proximity sensor comprising a dielectric film substrate having a sensor conductor on the front major surface thereof, and a guard conductor on the rear major surface thereof to provide an electrical shield for the sensor conductor; providing a vehicle bumper, the inwardly-curved internal surface of which is so shaped that it does not provide a substantially flat area for direct attachment thereto of the sensor, at least in the sensor conductor region; locating the sensor inside the bumper with the front and rear major surfaces of the sensor directed respectively towards and away from the bumper; and mounting the sensor to the inwardly-curved internal surface of the bumper in such a manner that the ingress and retention of water/dirt between the sensor and the bumper is inhibited (at least during normal use of the vehicle) but the sensor is maintained in a substantially flat condition, at least in the sensor conductor region.

[0015] In accordance with yet another aspect of the invention there is provided a method of making a vehicle bumper assembly comprising the steps of: providing a vehicle bumper; providing a capacitive proximity sensor comprising a dielectric film substrate having a sensor conductor on the front major surface thereof, and a guard conductor on the rear major surface thereof to provide an electrical shield for the sensor conductor; providing a former shaped to fit to the curved internal surface of the bumper; positioning the sensor on the former, with the rear major surface of the sensor directed towards the former; and inserting the former into the bumper to position the sensor on the internal surface of the bumper. The former may be an infill for the bumper, which remains in place within the bumper after the sensor has been positioned on the internal surface of the bumper.

[0016] The invention accordingly also provides a capacitive proximity sensor for mounting to a shaped surface of a body to sense the presence of external objects, the sensor comprising a dielectric film substrate having front and rear major surfaces that, in use, face respectively outwards and inwards of the body, a sensor conductor on the front major surface, and a guard conductor on the rear major surface to provide an electrical shield for the sensor conductor; the sensor being located on a former that is shaped to fit to the said shaped surface of the body whereby the former can be used to position the sensor on the said shaped surface. [0017] By way of example only, sensor assemblies in accordance with the invention will be described with reference to the accompanying drawings, in which:

BRIEF DESCRIPTION OF DRAWINGS

[0018] Fig. 1 shows a diagrammatic plan view of a major surface of a capacitive proximity sensor;

[0019] Fig. 2 shows an enlarged diagrammatic transverse cross-section of the sensor, taken on the line 2-2 of Fig. 1;

[0020] Fig. 3 shows a diagrammatic plan view of the sensor mounted on the internal surface of a vehicle bumper;

[0021] Fig. 4 shows a diagrammatic transverse cross-section taken on the line 4-4 of

Fig. 3;

[0022] Fig. 5 is similar to Fig. 3 but shows the sensor mounted in an alternative manner on the internal surface of the vehicle bumper;

[0023] Fig. 6 shows a diagrammatic transverse cross-section taken on the line 6-6 of

Fig. 5;

[0024] Fig. 7 is a diagrammatic plan view of a capacitive proximity sensor of the type shown in Figs. 1 and 2 with a differently- shaped substrate;

[0025] Fig. 8 shows a diagrammatic transverse cross-section of the sensor of Fig. 7, taken on the line 8-8, mounted on the internal surface of a bumper;

[0026] Fig. 9 shows a diagrammatic longitudinal cross-section of the assembly of Fig.

8;

[0027] Fig. 10 is similar to Fig. 3 but shows the sensor mounted in an alternative manner on the internal surface of the vehicle bumper;

[0028] Fig. 11 shows a diagrammatic transverse cross-section taken on the line 11-11 of Fig. 10;

[0029] Fig. 12 is a similar view to that of Fig. 11 but showing the sensor mounted in an alternative manner on the internal surface of the vehicle bumper;

[0030] Figs. 13 and 14 are similar views to Figs. 3 and 4 respectively but show the sensor mounted in an alternative manner on the internal surface of the vehicle bumper; [0031] Figs. 15 is a diagrammatic plan view of another capacitive proximity sensor of the type shown in Figs. 1 and 2;

[0032] Fig. 16 is an exploded diagrammatic transverse cross-section of the sensor of

Fig. 15, taken on the line 16-16, mounted on the internal surface of a bumper;

[0033] Fig. 17 is a diagrammatic illustration of a method of mounting a sensor of the type shown in Fig. 1 in a vehicle bumper; and

[0034] Figs. 18 to 20 are diagrammatic transverse cross-sections showing parts of other sensor assemblies in accordance with the invention.

DETAILED DESCRIPTION

[0035] The term "film substrate" as used herein refers to an article having an extension in two directions which exceeds the extension in a third direction, which is essentially normal to said two directions, by a factor of at least 5 and more preferably by at least 10. More generally, the term "film" is used herein to refer to a flexible sheet-like material, and includes not only films but also sheetings, foils, strips, laminates, ribbons and the like. [0036] The term "dielectric" as used herein refers to materials having a specific bulk resistivity as measured according to ASTM D 257 of at least 1 x 10¹² Ωcm and more preferably of at least 1 x 10¹³ Ωcm. The term "electrically-conductive" as used herein refers to materials having a surface resistivity as measured according to ASTM B 193-01 of less than 1 Ω/cm².

[0037] The capacitive proximity sensor 1 of Figs. 1 and 2 comprises a dielectric film substrate layer 2, the peripheral shape of which is determined by the intended location of the sensor as described further below. In Fig. 1, the substrate layer 2 is shown diagrammatically as being generally rectangular in shape.

[0038] The front major surface of the substrate layer 2 shown in Fig. 1 carries a sensor conductor 6 and a superguard conductor 7 that are spaced apart on the surface of the substrate layer, and electrically-isolated from one another by the intervening substrate material. The superguard conductor 7 comprises a flat, electrically-conductive strip extending essentially along the length of the substrate layer 2. The sensor conductor 6 exhibits a more complicated design and comprises several, optionally-flattened, conductive strips 6a extending parallel to one another essentially along the length of the substrate layer 2 and, adjacent both ends of the strips 6a, several additional parallel (but shorter), optionally-flattened, electrically-conductive strips 6b forming lobe type regions. The strips 6a, 6b of the sensor conductor are connected together in both lobe regions by electrically-conductive strips 6c extending at an angle across the whole array of strips 6a, 6b. It will be appreciated that the particular configuration and number of the strips 6a, 6b and 6c shown in Fig. 1 is not essential and could be modified. In Fig. 2, the sensor conductor 6 and the superguard conductor 7 are both shown as being attached to the substrate layer 2 by an adhesive 6', 7', respectively.

[0039] The rear major surface of the substrate layer 2, not visible in Fig. 1, carries a guard conductor 8 in the form of an electrically-conductive layer that preferably covers an area of the substrate corresponding in size at least to that occupied, on the other side, by the sensor conductor 6. In the sensor illustrated in Figs. 1 and 2, the guard conductor 8 essentially fully covers the rear surface of the substrate layer 2 to which it is attached (in this case, by an adhesive 8a). The guard conductor 8 is electrically-isolated from the sensor and superguard conductors 6, 7 by the intervening dielectric substrate layer 2. [0040] As so far described, the substrate layer 2, with the sensor conductor 6, the guard conductor 8 and the superguard conductor 7, can be attached to any suitable surface of a body, for example the inside of a bumper of a vehicle, to function as a capacitive proximity sensor. To that end, in the case of a vehicle bumper, the substrate layer is positioned with the front major surface of Fig. 1 (i.e. the surface carrying the sensor and superguard conductors 6, 7) directed outwardly from the vehicle and the rear major surface (i.e. the surface carrying the guard conductor 8) directed inwardly towards the vehicle. The conductors 6, 7, 8 are connected to an electronic control unit (not shown) that can monitor the change that occurs in the capacitance between the sensor conductor 6 and (electrical) ground as the vehicle approaches an external object, and thereby provide an indication to the driver of the distance between the sensor conductor (and, hence, the vehicle) and the object. During the monitoring process, the guard conductor 8 acts as a shield to reduce the sensitivity of the sensor conductor 6 to anything behind it in the direction of the body of the vehicle, while an electrical signal is applied to the superguard conductor 7 to make the guard conductor 8 appear even bigger and so minimize the effect, on the signal from the sensor conductor 6, of water drops running over the outside of the bumper in rainy weather conditions. Further information on the operation of a capacitive proximity sensor of that type can be obtained from, for example, WO 01/08925and GB-A- 2 400 666 mentioned above, and from GB- A-2 374 422 (also of AB Automotive Electronics Ltd.). The measurement and processing of signals from a capacitive proximity sensor are described, for example, in WO 02/19524 (also of AB Automotive Electronics Ltd.).

[0041] The entire sensor 1 can, if desired, be encased in a protective cover film (not shown).

[0042] In some cases, particularly when the surface of the body on which the sensor 1 is to be mounted is effectively flat or, if not flat, has a comparatively simple shape (for example, is curved in only one direction and/or has comparatively few irregularities), it may be possible to apply the sensor directly to the surface using, for example, an adhesive applied over the whole of the front surface of the sensor. In most cases, however, the surface on which the sensor is to be mounted will have a more complex shape (for example, it may be curved in two orthogonal directions and/or have irregularities such as projecting ribs) and considerable care will be required to prevent the formation of folds and creases in the sensor substrate layer 2 when it is being applied directly to the surface. In many cases, for example in use of the sensor on the internal, concavely-curved, surface of a vehicle bumper, it may be impossible to apply the sensor directly to a surface without allowing folds and/or creases to form in the substrate layer 2, or making suitably-shaped cuts in the substrate layer. Folds and/or creases in the substrate layer 2, particularly in the region of the sensor conductor 6, are undesirable because they may interfere with the correct functioning and durability of the sensor, for example by allowing water and/or dirt to penetrate and be retained between the sensor 6 and the supporting surface as already described. Cutting the substrate layer 2 so that it can be fitted to the supporting surface may enable a more satisfactory result to be obtained but is complex, time-consuming and costly.

[0043] Figs. 3 and 4 illustrate one way in which the sensor 1 can be attached to a shaped surface of a body without the formation of folds and/or creases in the substrate Iayer2 and without the need to cut the substrate layer 2 so that it can be tailored to fit the surface. In the example shown in Figs. 3 and 4, the sensor 1 is attached to the internal surface 10 of a vehicle bumper 11 but it will be appreciated that the sensor could be attached in a similar way to other shaped surfaces. [0044] In the assembly of Figs. 3 and 4, the sensor 1 is attached to the internal surface 10 of the vehicle bumper 11 only at the periphery 12 of the substrate layer 2 and, instead of following the inward curve of the bumper surface, extends in a substantially flat condition across the curve so that there is a gap 13 between the sensor and the bumper surface. The attachment of the periphery 12 of the sensor 1 to the bumper surface 10 can be effected in any suitable way (including, for example, by means of an adhesive or a weld) having regard to the nature of the substrate layer 2 and the surface to which it is being attached. In the particular case in which the substrate layer 2 is a polymeric film, suitable adhesives for attaching the periphery 12 of the sensor 1 to the bumper surface 10 include hot melt adhesives, for example the adhesive available under the trade designation "Jet-melt™ 3748 Adhesive" from 3M Company of St. Paul, Minnesota, USA and moisture/chemical curing adhesives, for example adhesives available under the trade designations "Scotch-Weld™ Structural Plastic Adhesives" and "Scotch-Weld™ Polyurethane Reactive Adhesives", also from 3M Company, while suitable welds include ultrasonic, fusion and laser welds. The attachment of the upper part of the sensor periphery 12 to the bumper surface 10, in particular, should form a seal that prevents water and/or dirt penetrating between the sensor and the bumper. The attachment of the remainder of the sensor periphery 12 to the bumper surface may form a similar seal but, in some cases, it may be sufficient or preferable to attach the remainder of the sensor periphery to the bumper surface at spaced locations only.

[0045] Figs. 5 and 6 show an assembly similar to that shown in Figs. 3 and 4 except that the sensor 1 is mounted on a non-metallic carrier substrate 15 having a larger surface area, with the rear face of the sensor located adjacent the carrier substrate. In this arrangement, it is the carrier substrate, rather than the sensor substrate layer 2, that is attached at its periphery 16 to the internal surface 10 of the vehicle bumper 11. Such an arrangement may be preferred if the size, shape or material of the sensor substrate layer 2 does not allow easy attachment of the sensor 1 directly to the bumper. The carrier substrate 15 could, for example, be a flexible film, a rigid injection-moulded component, a machined component, or an extruded polymeric sheet.

[0046] According to a modification, applicable to the assemblies of Figs. 3 and 4 and Figs. 5 and 6, the sensor 1 (or the larger substrate 15 on which it is mounted) is not attached directly at its periphery to the internal surface 10 of the bumper 11. Instead, the sensor is attached to the bumper by an attachment strip which has a flexible zone extending along its length at which the strip can bend to ensure the correct positioning of the sensor. Embodiments of that modification are illustrated in Figs. 18 to 20. [0047] In the embodiment illustrated in Fig. 18, the sensor 1 is attached to the internal surface 10 of a vehicle bumper 11 by an attachment strip 60 comprising two parts 61, 62 that are mechanically-interlocked along the length of the strip. The mechanical interlocking comprises a re-closable fastener 63 which permits the sensor 1 to be attached to, and removed from, the bumper 11 as required. In addition, hinges 64 are formed in the attachment strip 60, one along each side of the fastener 63 to provide increased flexibility. The re-closable fastener 63 may be of any suitable type, one example being a "press-to- close zipper" well known for use on plastic storage bags.

[0048] One part 61 of the attachment strip 60 is secured by foam tape 65 around the periphery of the sensor 1 (or, in the case of an assembly as shown in Figs. 5 and 6, the periphery of the larger substrate 15 on which the sensor is mounted). The other part 62 of the attachment strip 60 is secured by foam tape 66 in an appropriate position on the internal surface 10 of the bumper 11, selected to ensure that the sensor 1 extends in a substantially flat condition across the curve of the bumper as described above with reference to Figs. 3 to 6. The hinges 64 in the attachment strip 60 provide additional flexibility to enable the attachment strip to accommodate the curves in the bumper including, in many cases, even the curves in the end sections of the bumper. Depending on the shape of the sensor 1 and/or the bumper 11, it may not be necessary for the attachment strip 60 to extend around the entire periphery of the sensor: in some cases, for example, it may be sufficient to provide the attachment strip 60 only along the upper part of the periphery of the sensor.

[0049] The attachment strip 60 can be formed, for example by extrusion, from any suitable polymeric material. The re-closable fastener 63 may be omitted if there is no need to remove the sensor 1 from the bumper, provided that the hinges 64 themselves impart sufficient flexibility to the attachment strip 60 to enable it to accommodate the curves in the bumper 11. The foam tapes 65, 66 used to secure the attachment strip 60 to the sensor and to the bumper can be replaced by any suitable alternative including, for example, other forms of adhesive tapes, adhesive layers, and welds. As described above with reference to Figs. 3 and 4, the attachment of the upper part of the sensor periphery to the bumper surface 10, in particular, should form a seal that prevents water and/or dirt penetrating between the sensor and the bumper.

[0050] Fig. 19 illustrates a modification of the attachment system of Fig. 18. In this case, the part 62 of the attachment strip 60 is formed with a guidance channel 70 directly opposite the foam tape 66, in which an applicator roller (not shown) can be located to apply the foam tape 66 to the internal surface 10 of the bumper 11. In addition, the side 71 of the guidance channel adjacent the re-closable fastener 63 is formed with a lip 72 shaped to overhang the fastener and reduce the risk of moisture penetrating between the two parts of the fastener into the space between the sensor 1 and the bumper 11. It will be appreciated that the use of the guidance channel 70 is not restricted to attachment strips 60 incorporating re-closable fasteners: similar guidance channels could be used on attachment strips that do not incorporate re-closable fasteners, and could also be used on the substrate 15 of an assembly as shown in Figs. 5 and 6. In those cases, the lip 72 would not be required.

[0051] In the embodiment shown in Fig. 20, the re-closable fastener 63 of Figs. 18 and 19 is omitted and the attachment strip 60 (which is now a one-piece component) is formed with a hinge section 75 that allows the attachment strip 60 to be folded in half along its length as illustrated, thereby decreasing the area of the internal surface 10 of the bumper 11 that is occupied by the attachment strip.

[0052] Figs. 7 to 9 illustrate another way in which a capacitive proximity sensor 1 of the type shown in Figs. 1 and 2 can be attached to the internal surface 10 of a vehicle bumper 11, or to other shaped surfaces. In this case also, the sensor 1 is mounted on (for example, laminated to) a carrier substrate 20, with the rear face of the sensor located adjacent the carrier substrate. The carrier substrate 20 differs from that of Figs. 5 and 6 in that it is specifically shaped and pre-formed with bending lines 21 so that it can be adapted to the shape of the bumper in both the vertical and horizontal directions. The bending lines 21 are placed so that they lie outside the area of the carrier substrate that is occupied by the sensor conductor 6 (and, preferably, outside or at the edge of the area occupied by the sensor 1), thereby allowing the carrier substrate to be adapted closely to the shape of the bumper while the sensor conductor (and, possibly, the whole of the sensor or at least a major part of it) remains in a substantially flat condition. The carrier substrate 20 can be attached to the bumper surface 10 by an adhesive or by welding as described above with reference to Figs 3 to 6. Alternatively, because the carrier substrate 20 in this case may follow the shape of the bumper quite closely, it may be possible to use clips 22 or some other form of mechanical attachment means to secure the carrier substrate to the bumper. The mechanical attachment means 22 may be formed as an integral part of the bumper 11 and arranged to locate in pre-formed attachment holes 23 in the carrier substrate 20, thereby facilitating attachment of the sensor 1 to the bumper.

[0053] The arrangement illustrated in Figs. 7 to 9 results in a small gap between the sensor 1 and the internal surface 10 of the bumper 11, and is appropriate when the construction of the bumper reduces the risk of water and/or dirt entering and being retained in that gap. The construction of the bumper may, in some case, permit the passage of water (typically rain) through the gap but that may be acceptable particularly if the sensor 1 includes a superguard conductor as described above.

[0054] Figs. 10 and 11 show the use of a pre-formed support 25 for the sensor 1, the support being shaped on one side 26 to fit to the internal surface 10 of the bumper 11 and on the other side to provide a substantially flat surface 27 on which the sensor 1 is mounted. The support 25 may be formed from any suitable material that can be provided with the required shape, preferably a low density material such as a closed cell polymeric foam material. Suitable materials are polyethylene, polyurethane, and polystyrene foams. The support can be formed in a mould having the same shape as the bumper 11, or by machining. The support 25 may then be attached to the internal surface 10 of the bumper 11 by an adhesive, and the sensor 1 may likewise be adhesively-bonded to the support. Alternatively, the sensor 1 may first be attached to the bumper (for example, as described above with reference to Figs. 3 and 4) and the material for the support then injected into the gap between the sensor and the bumper.

[0055] Depending on the internal shape of the bumper 11 , it may be possible in some cases to omit the pre-formed support 25 of Figs. 10 and 11 and to laminate a sufficiently- thick layer of compressible material, for example a polymeric foam, to the front face of the sensor 1 to enable the sensor to fit smoothly inside the bumper. An arrangement of this type may be appropriate, for example, when the internal surface of the bumper is substantially flat except for the presence of some irregularities such as upstanding ribs. [0056] Fig. 12 illustrates a further modification of the arrangement shown in Figs. 3 and 4, in which the sensor 1 is attached at its perimeter to the bumper surface 10 by an adhesive foam strip 30 which may be continuous or in several pieces. As shown, the foam strip 30 extends around the entire perimeter of the sensor but that is not essential. If required, a further foam strip 31 could be located in the gap 13 between the sensor 1 and the bumper 11 to provide additional support for the sensor. A similar foam strip 31 could be provided, if required, in the gap 13 between the sensor 1 and the bumper 11 in the arrangements shown in Figs. 3 to 6. The foam strips 30, 31 may, for example, be commercially-available adhesive foam tapes.

[0057] A further use of a foam strip to attach the sensor 1 to the bumper 11 is illustrated in Figs. 13 and 14. In this case, a wider adhesive foam tape 35 is employed across the upper part of the sensor 1, in the area in which the sensor conductor 6 is located, to attach the sensor to the internal surface 10 of the bumper. The foam tape 35 inhibits the ingress and retention of water/dirt between the sensor and the bumper surface 10 in the area of the sensor conductor and also maintains that area of the sensor in a substantially flat condition. The lower part of the sensor, on the other hand, extends downwards towards the lower part of the bumper, hanging substantially freely and following the contours of the bumper surface 10. If desired, the lower part of the sensor 1 may be attached to the bumper surface 10, but only at spaced locations 36. The attachment at these spaced locations 36 may be made by patches of adhesive foam tape, or in any other suitable way.

[0058] Figs. 15 and 16 illustrate a modification of the arrangement shown in Figs. 13 and 14, in which a reinforcing strip 40 is additionally provided along the top of the sensor 1 on its rear major surface. The reinforcing strip 40 advantageously acts to curve the sensor into the bumper and assist the attachment of the sensor to the bumper surface 10 via the foam tape 35. As shown in Fig. 15, the reinforcing strip extends at each end beyond the sensor to provide locations at which it may be independently attached to the bumper 11. Fig. 16 shows, in cross-section, an exploded view of the sensor of Fig. 15 with the vehicle bumper 11 and, in addition to the reinforcing strip 40, shows the foam tape 35 and the adhesive layers 42, 43, 44 by which the strip 40, the sensor 1 and the foam tape 35 are attached to one another and to the bumper. Fig. 16 also shows a patch of adhesive tape 46 for attaching the lower part of the sensor 1 to the bumper 11 , and a release liner 45 for protecting the adhesive 44 on the foam tape 35 until the sensor 1 is placed in position in the bumper. [0059] Fig. 17 illustrates a method of mounting a sensor 1 of the type shown in Figs. 1 and 2 on the inside surface 10 of a vehicle bumper 11. The method requires the use of a former 50, the front face 51 of which is shaped to correspond to the shape of the internal surface 10 of the bumper. The former 50 could be shaped in a mould having the same shape as the bumper 11, or by machining. The sensor 1 is positioned on the front face 51 of the former 50 with the rear major surface of the sensor (i.e. the guard conductor 8) adjacent the face 51, where it is held in place in any suitable way, for example by means of a comparatively low-strength adhesive. Because the front face 51 is convex, it is easier to position the sensor adhesively on this face than on the inwardly-curved internal face of the bumper 11, and the procedure may be assisted by the provision of location points on the face 51 if required. When it is required to attach the sensor 1 to the internal surface 10 of the bumper 11, the front major surface of the sensor or the internal surface of the bumper is coated with an adhesive and the former 50 is then inserted into the bumper to deposit the sensor in the required position. The correct location of the sensor 1 can be achieved comparatively easily because the shape of the front face 51 of the former corresponds to that of the internal surface 10 of the bumper. The former 50 is then withdrawn and separates from the sensor 1 comparatively easily because the latter is now attached by a stronger adhesive to the bumper 11.

[0060] The former 50 is preferably re-usable and is formed from a low-cost material that can readily be moulded to the internal shape of the bumper. Advantageously, the front face of the former, at least, has a degree of resilience to assist in attaching the sensor 1 without the formation of noticeable folds and/or creases. A suitable material for the former is acrylonitrile-butadiene-styrene (ABS) copolymer. It is a further advantage if the sensor 1 can be stored on the former 50 in the required shape prior to use.

[0061] Alternatively, the former 50 could be a foam infill intended to remain inside the bumper in which case the bond between it and the sensor would be of a permanent nature. [0062] In the method illustrated in Fig. 17, an adhesive may be applied to the front face of the sensor 1 well in advance of the sensor being located in the bumper 11, in which case that adhesive may be protected by a release liner that is removed only when the sensor 1 is about to be attached to the internal surface 10 of the bumper.

[0063] In each of the arrangements described above, the superguard conductor 7 at the top of the sensor 1 is still located comparatively close to the internal surface of the bumper and consequently remains able to perform its intended function of minimizing the effect, on the sensor, of water drops running over the outside of the bumper in rainy weather conditions.

[0064] Although the above description relates in particular to the attachment of the sensor 1 to the internal surface of the vehicle, there are many other situations in which capacitive proximity sensors may be used and may need to be attached to a shaped surface. For example, in the case of vehicles, proximity sensors can be used on any non- conductive panels such as door panels and bonnet lids for the purpose of detecting impending impacts and activating the appropriate safety mechanisms (e.g. air bags). Capacitive proximity sensors may be used in moving objects such as robot arms for controlling movement and preventing collisions, or in detectors for responding to moving objects (such as sensors for controlling automatic doors so that they respond to the approach of people or objects). Capacitive proximity sensors may also be used for detecting if a space is occupied, for example inside a vehicle to determine if an individual seat is occupied and activation, if necessary, of a warning signal to indicate that the corresponding seat belt is not being used. A further use of a capacitive proximity sensors is as a touch sensors that is activated when a person or object touches it either directly or through a thin insulator layer. Many other uses will be apparent to those skilled in the art, and the specific uses mentioned above are provided as examples only.

Claims

What is claimed is:

1. A sensor assembly comprising a capacitive proximity sensor mounted to a surface of a body to sense the presence of external objects, wherein:

(i) the sensor comprises a dielectric film substrate having front and rear major surfaces that, in use, face respectively outwards and inwards of the body, a sensor conductor on the front major surface, and a guard conductor on the rear major surface to provide an electrical shield for the sensor conductor;

(ii) the said surface of the body is so shaped that it does not provide a substantially flat area for direct attachment thereto of the sensor, at least in the sensor conductor region; and

(iii) the sensor mounting is such that the ingress and retention of water/dirt between the sensor and the said surface is inhibited, and the sensor is maintained in a substantially flat condition, at least in the sensor conductor region.

2. A sensor assembly as claimed in claim 1, in which the said surface of the body is an internal surface of the body.

3. A sensor assembly as claimed in claim 1 or claim 2, in which the said surface of the body is inwardly-curved.

4. A sensor assembly as claimed in claim 1, in which the body is a vehicle bumper and the said surface of the body is the inwardly-curved internal surface of the bumper.

5. A sensor assembly as claimed in claim 4, in which the sensor substrate is attached at its periphery directly to the internal surface of the bumper in such a manner that the sensor substrate extends in a substantially flat condition across the inward curve of the internal surface.

6. A sensor assembly as claimed in claim 4, in which the sensor substrate is mounted on a carrier substrate that is attached at its periphery directly to the internal surface of the bumper in such a manner that the carrier substrate extends in a substantially flat condition across the inward curve of the internal surface.

7. A sensor assembly as claimed in claim 5 or claim 6, in which the attachment of the upper part of the periphery of the sensor/carrier substrate to the internal surface of the bumper forms a seal that inhibits the ingress of water/dirt between the sensor and the bumper.

8. A sensor assembly as claimed in claim 7, in which the remainder of the periphery of the sensor/carrier substrate is attached to the internal surface of the bumper at spaced locations.

9. A sensor assembly as claimed in any one of claims 5 to 8, in which the sensor/carrier substrate is welded or adhesively-bonded to the internal surface of the bumper.

10. A sensor assembly as claimed in claim 4, comprising a sensor support that is attached inside the bumper, the support being shaped, on one side, to fit to the internal surface of the bumper and, on the other side, with a flat surface on which the sensor is mounted.

11. A sensor assembly as claimed in claim 10, in which the support comprises a foam material.

12. A sensor assembly as claimed in claim 4, in which the sensor is attached to the internal surface of the bumper by a foam material.

13. A sensor assembly as claimed in claim 12, in which the front major surface of the sensor is laminated to a layer of foam material that is attached to the internal surface of the bumper.

14. A sensor assembly as claimed in claim 12, in which the sensor is attached to the internal surface of the bumper by at least one foam strip at the periphery of the sensor substrate.

15. A sensor assembly as claimed in claim 14, in which a foam strip at the upper part of the sensor substrate forms a seal that inhibits the ingress of water/dirt between the sensor and the bumper.

16. A sensor assembly as claimed in claim 15, in which the lower part of the sensor is attached to the internal surface of the bumper at spaced locations.

17. A sensor assembly as claimed in any one of claims 12 to 16, in which the foam is adhesively attached to the sensor and to the internal surface of the bumper.

18. A sensor assembly as claimed in claim 4, in which the sensor substrate is bent to follow the inward curve of the internal surface while maintaining the sensor conductor region in a substantially flat condition.

19. A sensor assembly as claimed in claim 18, in which the sensor is attached to the internal surface of the bumper by mechanical attachment means.

20. A sensor assembly as claimed in claim 19, in which the mechanical attachment means are located in pre-formed apertures in the sensor substrate.

21. A sensor assembly as claimed in claim 4, in which the sensor mounting comprises a re-closable mechanical fastener, whereby the sensor can be removed from, and replaced in, the vehicle bumper.

22. A sensor assembly as claimed in claim 4, in which the sensor mounting comprises an attachment strip extending along the periphery of the sensor and connecting the sensor to the internal surface of the bumper, wherein the attachment strip has a longitudinally- extending hinge region about which the attachment strip can flex.

23. A sensor assembly as claimed in claim 22, in which the attachment strip is welded or adhesively-bonded to the internal surface of the bumper and/or to the sensor.

24. A capacitive proximity sensor for mounting to a surface of a body to sense the presence of external objects, the sensor comprising a dielectric film substrate having front and rear major surfaces that, in use, face respectively outwards and inwards of the body, a sensor conductor on the front major surface, and a guard conductor on the rear major surface to provide an electrical shield for the sensor conductor; wherein the sensor substrate is pre-formed with bending lines along which the sensor can be bent to shape it for attachment to the said surface of the body.

25. A sensor as claimed in claim 24, in which the bending lines are located outside the region of the substrate on which the sensor conductor is located.

26. A sensor as claimed in claim 24 or claim 25, wherein the sensor substrate is provided with pre-formed apertures by which the sensor can be attached to the said surface of the body.

27. A method of making a vehicle bumper assembly comprising the steps of:

(i) providing a capacitive proximity sensor comprising a dielectric film substrate having a sensor conductor on the front major surface thereof, and a guard conductor on the rear major surface thereof to provide an electrical shield for the sensor conductor;

(ii) providing a vehicle bumper, the inwardly-curved internal surface of which is so shaped that it does not provide a substantially flat area for direct attachment thereto of the sensor, at least in the sensor conductor region;

(iii) locating the sensor inside the bumper with the front and rear major surfaces of the sensor directed respectively towards and away from the bumper; and

(iv) mounting the sensor to the inwardly-curved internal surface of the bumper in such a manner that the ingress and retention of water/dirt between the sensor and the bumper is inhibited but the sensor is maintained in a substantially flat condition, at least in the sensor conductor region.

28. A method of making a vehicle bumper assembly comprising the steps of: (i) providing a vehicle bumper;

(ii) providing a capacitive proximity sensor comprising a dielectric film substrate having a sensor conductor on the front major surface thereof, and a guard conductor on the rear major surface thereof to provide an electrical shield for the sensor conductor;

(iii) providing a former shaped to fit to the curved internal surface of the bumper;

(iv) positioning the sensor on the former, with the rear major surface of the sensor directed towards the former; and

(v) inserting the former into the bumper to position the sensor on the internal surface of the bumper.

29. A method as claimed in claim 28, including the step of withdrawing the former from the bumper after the sensor has been positioned on the internal surface of the bumper.

30. A method as claimed in claim 28 or claim 29, in which the sensor is attached to the internal surface of the bumper by an adhesive.

31. A method as claimed in any one of claims 28 to 30, including the step of applying adhesive to the front major surface of the sensor, protecting the adhesive with a release liner, and removing the release liner before the sensor is positioned on the internal surface of the bumper.

32. A capacitive proximity sensor for mounting to a shaped surface of a body to sense the presence of external objects, the sensor comprising a dielectric film substrate having front and rear major surfaces that, in use, face respectively outwards and inwards of the body, a sensor conductor on the front major surface, and a guard conductor on the rear major surface to provide an electrical shield for the sensor conductor; the sensor being located on a former that is shaped to fit to the said shaped surface of the body whereby the former can be used to position the sensor on the said shaped surface.

33. A sensor as claimed in claim 32 for mounting to the inwardly-curved internal surface of a vehicle bumper, in which the former is an infill for the bumper.

34. A sensor assembly as claimed in claim 4, in which the sensor further comprises a superguard conductor on the front major surface of the substrate, the sensor mounting being such that the superguard conductor is located comparatively close to the inwardly- curved internal surface of the bumper.