WINDSHIELD MONITORING SYSTEM

Abstract

The present invention relates to a windshield monitoring system, comprising; a windshield (104) for a vehicle (100); a plurality of light emitters (108) forming an array, each emitter (108) arranged to direct a beam of light into an edge of the windshield (104) at an angle of incidence arranged to subject the beam of light to total internal reflection at a windshield to air interface to propagate the beam of light across the windshield to an opposing edge thereof, and the angle of incidence being arranged to refract the light beam away from the windshield at a windshield to contaminant interface; the system comprising a light detector arranged to detect that light from the beam of light has been refracted away from the windshield; and wherein the emitters (108) are separated substantially across a length of the windshield (104).

Claims

1. A windshield monitoring system, comprising at least one array of light emitters, each light in the at least one array arranged to direct a beam of light into an edge of a vehicle windshield at an angle of incidence arranged to subject the beam of light to total internal reflection at a windshield to air interface to propagate the beam of light across the windshield to an opposing edge thereof, the angle of incidence being arranged to refract the light beam away from the windshield at a windshield to contaminant interface; and a light detector arranged to detect that light from the beam of light has been refracted away from the windshield; wherein the light emitters are separated substantially across a length of the windshield.

2-5. (canceled)

6. The system of claim 1, wherein each light emitter comprises a pulsar to pulsate the light beam according to a predefined pattern.

7. The system of claim 6, wherein each light beam is pulsated, strobed or shuttered at a unique predefined pattern or is phase shifted relative to other light pulse patterns.

8. The system of claim 1, wherein the at least one array substantially spans along a side edge of the windshield.

9. The system of claim 1, wherein the at least one array comprises two arrays of light emitters, and wherein the two arrays are orthogonal.

10. (canceled)

11. The system of claim 1, wherein the light detector is arranged to monitor an interior face of the windshield.

12. (canceled)

13. The system of claim 9, further comprising an association module arranged to determine a coordinate position of the contaminant by associating the light from the beam of light that has been refracted away from the windshield with one or more emitters from each array.

14. The system of claim 1, further comprising a noise filter arranged to distinguish light emitted from the light emitters from other light.

15-16. (canceled)

17. A windshield clearing system, comprising; the windshield monitoring system of claim 1; a windshield clearing element on the windshield; and a control module arranged to control the windshield clearing element to heat an area of the windshield where light has been refracted.

18. (canceled)

19. The windshield clearing system of claim 17, wherein the windshield clearing element comprises a heating mechanism, wherein the heating mechanism comprises a plurality of heating elements, and wherein the control module is arranged to heat a heating element corresponding to the location of the detected contaminant.

20-21. (canceled)

22. The system of claim 19, further comprising a termination module arranged to terminate heating of the heating element in response to the windshield monitoring system ceasing to detect refracted light or after a predetermined time period.

23. A windshield for a vehicle or vehicle comprising the windshield monitoring system as claimed in claim 1.

24. A method of monitoring a windshield, the method comprising; emitting a plurality of light beams via a respective plurality of light emitters into an edge of the windshield at an incidence angle arranged to subject the light beams to total internal reflection at a windshield to air interface to propagate across the windshield and the angle of incidence being arranged to refract one or more of the plurality of light beams away from the windshield at a windshield to contaminant interface, the plurality of light beams being separated so as to substantially span a length of the windshield; and detecting a presence of light refracted away from the windshield.

25. The method of claim 24, further comprising pulsating, strobing, or shuttering the plurality of light beams.

26. (canceled)

27. The method of 24, wherein the emitting the plurality of light beams is carried out substantially along adjacent mutually orthogonal edges of the windshield.

28. The method of claim 24, further comprising filtering out noise detected by a light detector.

29. The method of claim 26, further comprising associating the refracted light with one of the plurality of light emitters.

30. A method of clearing a windshield, comprising detecting surface contamination using the method of claim 24, and heating an area of the windshield in response to detecting the surface contamination.

31. The method of claim 30, further comprising dividing the windshield into a plurality of zones and heating a zone corresponding to a location of the detected surface contamination.

32. The method of claim 30, further comprising terminating heating of the area in response to ceasing to detect refracted light or after a predetermined time period.

33. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0103] One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0104] FIG. 1A shows a windshield monitoring system according to the prior art;

[0105] FIG. 1B shows a similar view to FIG. 1A;

[0106] FIG. 2 shows a windshield monitoring system according to a first embodiment of the present invention;

[0107] FIG. 3 shows a block diagram of the windshield monitoring system of FIG. 2;

[0108] FIG. 4 shows a schematic of a windshield clearing system including the windshield monitoring system of FIG. 2;

[0109] FIG. 5 shows a section view of the windshield monitoring system of FIG. 2 in operation;

[0110] FIG. 6 shows a similar view to FIG. 2 of a windshield monitoring system according to a second embodiment of the present invention;

[0111] FIG. 7 shows a similar view to FIG. 3 of a second embodiment of the present invention;

[0112] FIG. 8 shows part of a windshield monitoring system according to a third embodiment of the present invention;

[0113] FIG. 9 shows a block diagram of the windshield monitoring system of FIG. 8;

[0114] FIG. 10 shows a windshield clearing system according to another aspect of the third embodiment of the present invention;

[0115] FIG. 11 shows a section view of the windshield monitoring system of FIG. 8, in operation not detecting contamination;

[0116] FIG. 12 shows a similar view to FIG. 11 of the windshield monitoring system detecting contamination; and

[0117] FIG. 13 shows a windshield clearing system of a windshield monitoring system according to a fourth embodiment of the invention.

DETAILED DESCRIPTION

[0118] With reference to FIG. 2, a vehicle 100 includes a vehicle frame 102 supporting at least one windshield 104 dividing the vehicle interior and the vehicle exterior. The term windshield covers a front windscreen, a rear windscreen, and a side window. Each windshield 104 either comprises a plurality of sheets of laminated glass or a singular sheet of glass. For instance, a laminated glass windshield 104, as shown in FIG. 5, is constructed using an inner sheet of glass 105, an outer sheet of glass 107, and an intermediate layer 109 of Polyvinyl Butyral (PVB) sandwiched between the two. The intermediate layer 109 is made from PVB to prevent shards of glass flying off in a crash and because PVB has the same refractive index as the inner 105 and outer 107 sheets of glass.

[0119] The vehicle 100 also includes a windshield monitoring system. FIG. 2 shows part of the windshield monitoring system with FIG. 3 showing a more detailed version in the form of a block diagram.

[0120] With continued reference to FIG. 2, the windshield monitoring system includes an array of light emitters 108. The light emitters are provided in the form of Light Emitting Diodes (LEDs). The emitters 108 are separated from one another to span over a length, such that the light they emit spans the width of the 104. The emitters 108 are separated substantially equidistantly from one another. The emitters 108 are arranged to emit a narrow beam of light 106, specifically narrow beams of monochromatic light. Monochromatic light is used in contrast to white light since white light would disperse within the windshield. The array of emitters 108 is provided along one side of the windshield. In particular, the emitters 108 are encapsulated along the side of the windshield 104 within a refractive index matched medium. As will be described in more detail below, the emitters are arranged to direct the beams of light 106 into the windshield at an angle of inclination of between about 43 and about 65.

[0121] The windshield monitoring system also includes a detector. Specifically, the detector is a camera 110. The camera 110 is a digital camera able to distinguish a position of a detected image by pixels. The camera 110 may be located in the vehicle interior. The camera 110 may be sensitive to all wavelengths of visible light, or may alternatively be sensitive only to a specific wavelength or waveband corresponding to the beams of light produced by the light emitters 108. When monitoring the front windscreen, the camera 110 is integrated into a ceiling panel of the vehicle 100 in between a rear view mirror (not shown) and the windshield 104. Alternatively, the camera may be mounted at the top of the dashboard. The camera is oriented so as to monitor an interior surface 112 of the front windscreen. As will be described in more detail below, the camera 110 can thus detect any refracted light 114 as a result of surface contamination 116. Due to the camera 110 dividing a recorded image up by pixels, the location of the refracted light 114, and thus the location of contamination 116, can be determined directly by mapping the pixel(s) detecting the reflected light onto a map of the windshield 104.

[0122] With reference to FIG. 3, the example shown of the windshield monitoring system also includes a noise filter 119, which noise filter 119 includes a pulsar 120 and a lock-in amplifier 122. The function of each of these components will be described in more detail below. However in summary, the pulsar 120 includes a motor 124 and a disc 126. The disc is rotatable about an axis (not shown). The motor 124 is coupled to the disc 126 so as to rotate the disc 126 in operation. The disc 126 includes successive transparent 128 and opaque 130 regions. Light from a light beam 106 is allowed to pass though the transparent regions 128. However, light beams 106 are blocked by the opaque regions 130. The axis of rotation of the disc 126 is misaligned with the beam of light 106 such that the beam of light 106 impinges on whichever of the transparent 128 or opaque 130 regions it is aligned with.

[0123] As an alternative to pulsating the light beam using the disc 126, the light beam can be pulsated by strobing or shuttering by flickering the light beam on and off using control logic stored on a computer on board the vehicle.

[0124] The lock-in amplifier 122 communicates with the motor 124 so as to obtain the rotational speed of the disc 126. The lock-in amplifier 122 also has a data store having information regarding the geometric profiles of the transparent and opaque regions 128, 130. In this way, the lock-in amplifier can associate light detected as a result of the beam of light 106 from other light 132, for instance natural light or light from oncoming vehicle headlights.

[0125] With reference to FIG. 4, the vehicle 100 also includes a windshield clearing system 140. The windshield clearing system 140 includes a control module 142 and a heating mechanism 144.

[0126] The control module 142 is provided as electronic data on a non-volatile memory component of an on-board vehicle computer. The computer also includes a processor for executing the electronic data. Operation of the control module 142 is described in more detail below. However, the control module 142 receives inputs from the windshield monitoring system. Specifically, the control module 142 receives an indication as to the presence and location of any detected refracted light 114. The control module 142 then commands a heating zone 144 at a location of the detected refracted light to heat up to clear the responsible contamination.

[0127] The control module 142 includes a termination module 145 as part of the electronic data stored on the memory component of the on-board computer. The termination module 145 is arranged to send a termination command to the heating zone 144 to terminate heating in response to the camera 110 (FIG. 2) ceasing to detect refracted light 114.

[0128] The heating mechanism 144 includes a plurality of active heating elements 146 and passive heating elements 148. The active heating elements 146 include resistance heating elements arranged to increase in temperature when an electrical current is passed across them. The resistance heating elements may be provided as vapour deposited metallic layers. The metallic layers can be fabricated from any metallic element or alloy suitable for conducting heat in by electrical resistance. One such metal allow is an alloy including silver. However, other electrically conductive materials may be used. For instance, an organic material, such as graphene, may be used. The passive elements 148 are boundaries of the active heating elements 146 and are provided as areas of uncoated glass to provide insulated areas intermediate the active heating elements 146. These uncoated areas are relatively narrow so as to prevent a pattern of unclear windshield. It can be visualised that the windshield is thus divided into a plurality of zones by virtue of the active and passive heating elements 146, 148.

[0129] With reference to FIG. 5, in operation, light from an emitter 108 is shone as a beam of light 106 into an edge of the windshield 104. The light beam 106 is directed into the windshield 104 at an angle of incidence .sub.i relative to a normal line of incidence N of the windshield 104. The angle of incidence .sub.i is between about 43 and about 65. It will be appreciated that the windshield in FIG. 5 is of a laminated glass construction though the same angles of incidence would be applicable to a windshield made from a singular sheet of glass.

[0130] The lower limit of about 43 is chosen since this is the critical angle .sub.c of a glass to air interface. The critical angle .sub.c is the angle at which light reflects internally with no light escaping from the glass to the air. This phenomenon is known as total internal reflection. Any angle of incidence greater than the critical angle .sub.c also subjects the light beam to total internal reflection. The angle of incidence, .sub.i, being greater than the critical angle of 43 is sufficient to subject the beam of light 106 to total internal reflection at a glass to air interface to propagate the beam of light 106 across the windshield 104 to an opposing edge thereof. In particular, the light beam 106 is reflected off both interior and exterior surfaces to propagate the light beam 106 across the windshield 104.

[0131] The upper limit of about 65 is the critical angle, .sub.c, for a glass to water interface. In the same way, a beam of light 106 impinging on a glass to water interface at an angle of incidence, .sub.i, greater than 65 would reflect internally whereas an angle of incidence lower than 65 would refract light away from the windshield 104 as refracted light 114. An initial angle of incidence .sub.i is selected to be lower than the critical angle .sub.c of glass to water in order to intentionally refract light 114 away from the windshield 104 when in contact with any water based contamination 116. In this way, the angle of incidence .sub.i is arranged to refract the light beam 106 away from the windshield 104 at a glass to water/contaminant interface.

[0132] Water based contamination benefits most from this clearing system since water is more easily cleared up by heating than other types of contamination such as dirt. Water based contamination 116 includes water vapour, liquid water, and ice.

[0133] Any refracted light 114 is detected by the camera 110. Any light detected by the camera 110 which has not been pulsated by the pulsar 120 (FIG. 3) will be filtered out by the noise filter 119.

[0134] Since the camera 110 can distinguish the location of refracted light 114 on the windshield 104, the control module (FIG. 4) configures the corresponding active heating element 146 covering the area of contamination 116 to heat up. Heating the area of contamination 116 will evaporate the water responsible for the contamination 116.

[0135] The termination module 145 sends a termination command to stop passing electrical current through the active heating element 146 when the camera 110 ceases to detect refracted light 114. In addition, the termination module 145 sends a termination command to stop passing electrical current through the active heating element 146 after a predetermined time period. This is particularly important in instances where false positives occur. For instance, a false positive may be triggered for windshield defects such as chips or cracks which will never be cleared by any of the vehicle's on board ancillary systems. Providing the termination command after the predetermined time period thus prevents wasted energy for non-treatable windshield contamination scenarios.

[0136] The advantages of the previous embodiment are numerous. One particular advantage is that by providing detection over a wide area of the windshield 104, less energy is ultimately consumed since any contamination 116 is detected early. This is particularly important for electric or hybrid electric vehicles where power consumption is critical to the range of the vehicle. In addition, dividing the windshield into zones of separate heating elements provides further efficiencies since uncontaminated areas are not directly heated.

[0137] With reference to FIGS. 6 and 7, a second embodiment of the windshield monitoring system will now be described. FIG. 6 shows part of the windshield monitoring system with FIG. 7 showing a more detailed version in the form of a block diagram. It is possible to transfer those features described specifically with reference to the first embodiment to the second embodiment. Those features of the second embodiment which are common to the first embodiment are labelled 100 greater.

[0138] The windshield monitoring system includes two arrays of emitters 208. The arrays are mutually orthogonal and are provided along adjacent edges of the windshield 204. Specifically, the arrays are positioned along a bottom edge and a right side edge of the windshield 204. The emitters 208 are again separated so as to span along each edge of the windshield to provide coverage over the majority of the windshield 204. The emitters 208 are oriented to emit beams of light 206 into the windshield 204 at an angle of incidence of between about 43 and about 65. These angles are selected for the same reasons as described above. The emitters 208 are also oriented so that the light beams 206 are substantially parallel.

[0139] The light detector in this embodiment is a photodiode 210 as opposed to a camera. The photodiode 210 can detect the presence of light, and depending on the type of photodiode used, may tuned to be sensitive only to a specific wavelength or band of wavelengths of light as may be produced by the light emitters, but cannot distinguish the location of light, like the camera 110. In order to determine the location of contamination 216, the windshield detection system associates the detected light with one light emitter 208 from each array.

[0140] With reference to FIG. 7, the windshield monitoring system again includes a pulsar 220 and a lock-in amplifier 222 which work in the same way as the previous embodiment. However, each light beam 206 is pulsated at a unique predefined pattern and/or frequency of pulsation. The windshield monitoring system also includes an association module 270. The association module 270 is provided as electronic data on the memory component of the on-board computer, like the control module.

[0141] The association module 270 includes a data store for storing data relating to the pulse patterns for each emitter 208. In response to the photodiode 210 detecting a light pulse, the association module 270 compares the pulsed refracted light beam with those stored for each emitter 208. By matching the light pulse to the responsible emitter 208 in each array, the association module locates the position of the contamination 216 with a 2 dimensional coordinate. For instance, the association module may determine that contamination exists in the centre of the windshield 204 if a central emitter 208 from each array is identified as being responsible for the refracted light 214 (FIG. 6). This coordinate is then fed into the control module (FIG. 4) to control a heating zone corresponding to an area at which contamination 216 has been detected.

[0142] As an alternative to pulsating the light beam 206, the light beams 206 could be phase shifted relative to the other beams of light 206.

[0143] A third embodiment of the invention will now be described. With reference to FIG. 8, a vehicle 300 includes a frame 302 supporting a plurality of windshields 304 (one shown). The term windshield 304 includes a front windscreen, or a rear windscreen, or a side window, of which there are several. Each windshield 304 either comprises a plurality of sheets of laminated glass or a singular sheet of glass.

[0144] With brief reference to FIG. 11, a laminated windshield 304 includes a plurality of sheets. Said sheets include outer and inner sheets of glass 306, 307, an infrared reflective (IRR) film 308, and an intermediate layer 309. The intermediate layer 309 is made from Polyvinyl Butyral (PVB). PVB is selected because it has the same refractive index as the inner 307 and outer 306 sheets of glass. The windshield 304 separates an exterior environment 310 from an interior environment 312. Accordingly, the windshield 304 has an exterior surface 316 and an interior surface 314.

[0145] With reference to FIGS. 8 and 9, the vehicle 300 also includes a windshield monitoring system, part of which is shown in FIG. 8 with a more detailed version in the form of a block diagram being provided in FIG. 9.

[0146] With specific reference to FIG. 8, the windshield monitoring system includes a light source in the form of a plurality of light emitters 320. The light emitters are Light Emitting Diodes (LEDs). The light emitters are configured to emit beams 322 of infrared light. The beams 322 are narrow beams of light. The emitters 320 are provided as two arrays of emitters. The arrays of emitters are arranged along adjacent, mutually orthogonal edges of the windshield 304. In particular, one array is provided along a right hand side edge of the windshield 304. The other array is provided along a lower horizontal edge of the windshield 304. The two arrays of light emitters 320 are thus mutually orthogonal. Each emitter 320 is arranged to direct a beam of infrared light 322 in to the windshield 304 at an angle of incidence, .sub.i, relative to a normal line of incidence N between about 42 and about 65. The reasons for this are provided in more detail below. The light emitters 320 span along each respective edge of the windshield 304. Beams of light 322 from the same array are substantially parallel to one another. In this way, almost complete coverage of the windshield can be provided by the two mutually orthogonal arrays of light emitters 320. Each emitter 320 is encapsulated in a refractive index matched medium along the edge of the windshield.

[0147] The windshield monitoring system also includes a plurality of light detectors 324. Each light detector is a photodiode. The light detectors 324 are also provided as two mutually orthogonal arrays. The two arrays of light detectors 324 are provided along a left side edge of the windshield 304 and a top edge of the windshield 304 respectively. Each light detector 324 is associated with a unique light emitter 320 such that there are equal numbers of light detectors and emitters. The light detectors 324 have the same separation distance as the light emitters 320. As will be described in more detail below, the light detectors 324 are arranged to detect the intensity of light reflected internally within the windshield 304 from the corresponding emitter 320 at the opposing edge of the windshield 304.

[0148] As will be described in more detail below, any contamination 326 on the windshield may result in a light beam 322 being refracted away from the windshield 304. Refracted light 328 causes a drop in intensity of the internally reflected light 322 detected by the light detector 324.

[0149] With specific reference to FIG. 9, the windshield monitoring system includes a noise filter 329 to distinguish light emitted from the light source from other detected light. The noise filter comprises a pulsar 330 and a lock-in amplifier 332.

[0150] The pulsar 330 includes a motor 334 and a rotatable disc 336. The motor 332 is arranged to rotate the disc about a rotation axis (not shown) at a variable speed measure in revolutions per minute (RPM). The disc includes successive transparent 338 and opaque 340 regions. A light beam 322 emitted from the light emitter 320 is directed in to the disc 336. The light beam 322 impinges on the successive transparent 338 and opaque 340 regions since the axis of rotation of the disc 336 is misaligned with the light beam 322. The light beam 322 is allowed to pass through the transparent regions 338 but is blocked by the opaque regions 340. By opaque, it is meant that any material can be used which blocks out infrared light. The transparent 338 and opaque 340 regions are not consistent in area so as to vary the duration of light passing the disc 336. In this way, the pulsar 330 is arranged to pulsate the light according to a predefined pattern corresponding the sizes of the transparent 338 and opaque 340 regions and the speed at which the motor 334 drives the disc 336.

[0151] The disc 336 and/or the speed of the motor 334 are varied across the array of light emitters 320 such that each light beam 322 is pulsated according to a unique pattern. In this way, light can be identified as originating from a specific light emitter 320. Another way in which this can be achieved is to phase shift light from each of the light emitters 320 relative to the other light emitters 320.

[0152] The lock-in amplifier 332 is connected to the motor 334 to monitor the RPM thereof. The lock-in amplifier 332 also includes a data store for storing the geometric profiles of the rotatable discs 336. The lock in amplifier can compare the received light with that calculated as being an expected pattern of light such that the light beam 322 originating from the light emitter 320 can be distinguished from other light 342 originating from a variety of other sources.

[0153] As an alternative, the pulsar may use strobing effects or shuttering to pulsate the light beam rather than using the disc 336 as described above.

[0154] The windshield monitoring system also includes a locating module 344 which is linked to the light detectors 324. Any light detected by a specific light detector 324 can be used to locate the position of the contamination as a two dimensional coordinate by identifying which detector 324 in each array has detected the refracted light.

[0155] With reference to FIG. 10 the vehicle 300 also includes a windshield clearing system 350. The windshield clearing system 350 includes the windshield monitoring system, a control module 352, and a clearing element, in this embodiment in the form of a heating mechanism 354.

[0156] The control module 352 is provided as electronic data on a non-volatile memory component of an on board computer system. The computer system also includes a processor to execute the electronic data to operate the control module 352. The locating module 344 is also provided in the same way, namely, electronic data stored on the non-volatile memory component of the on board computer. The control module 352 is arranged to apply a voltage across the heating mechanism 354 in response to a demand to heat the heating element to clear the contamination.

[0157] The control module 352 includes a termination module 353 as part of the electronic data stored on the memory component of the on-board computer. The termination module 353 is arranged to send a termination command to the heating mechanism 354 to terminate heating in response to the detectors 324 (FIG. 9) ceasing to detect refracted light 328.

[0158] The heating mechanism 354 is divided in to a plurality of zones, or heating elements. The zones are divided in to active heating elements 356 and passive heating elements 358. Active heating elements 356 are defined as those that can be heated and are provided with electrically conductive layers. These passive zones 358 are very small in dimension so as to prevent a pattern of unclear glass during operation. These passive zones 358 are considered as boundaries to the active zones 356. The control module 352 can apply a voltage across the metallic layer of any of the active heating elements 356. The corresponding electrical current heats a zone of the windshield corresponding to the location of the detected contamination.

[0159] The heating mechanism 354 comprises a resistant heating element which is a metallic layer. The metallic layer is vapour deposited on to the windshield 304. The metallic layer is silver alloy. However, other electrically conductive materials would suffice, for instance some organic materials like graphene, or even the IRR layer itself.

[0160] With reference to FIG. 11, in operation, the light emitter 320 emits a beam of infrared light 322 in to an edge of the windshield 304 such that the angle of incidence of the light on the glass to air interface is between about 43 and about 65. These angles are measured relative to a normal angle of incidence N relative to the interior and exterior surfaces 314 and 316 of the windshield 304.

[0161] The critical angle, .sub.c, for a glass to air interface is about 43. The critical angle, .sub.c, for a glass to water interface is about 65. The difference in critical angle is due to the difference in refractive index between air and water. Any light below an angle of incidence, .sub.i, lower than a critical angle, .sub.c, would refract away from the glass. Any angle of incidence, .sub.i, above the critical angle, .sub.c, would reflect internally within the glass. This phenomenon is total internal reflection.

[0162] This windshield clearing system is most suitable for use in clearing water based contamination such as moisture (in the form of fogging or misting of the windshield), ice, and liquid water since water evaporates relatively easily through heat. Accordingly, an angle of incidence, .sub.i, of a beam of light 322 between about 43 and about 65 would reflect internally at a glass to air interface and refract away from the glass at a glass to contaminant interface.

[0163] The light detector 324 constantly monitors the intensity of light reflected internally across the windshield 304. Since the light beam 322 is infrared light, the light naturally reflects off the IRR layer 308 inside the laminated windshield 304. In this way, a light beam 322 can be directed on an interior side of the IRR layer 308. Additionally, or alternatively, the light beam 322 can be directed on an exterior side of the IRR layer 308. This can be achieved by directing adjacent emitters 320 to direct their beam of light 322 on opposite sides of the reflective IRR layer 308. Alternatively, a pivoting mechanism can be used to pivot an emitter 320 such that one pulse of light 322 can be directed on the interior side of the IRR layer 308 and a subsequent pulse of light 322 from the same emitter can be directed to an exterior side of the IRR layer 308.

[0164] With reference to FIG. 12, any contamination 326 changes the critical angle, .sub.c, at the interface as described above. When the light beam 322 impinges on a glass to contaminant interface, light is refracted away from the windshield 304 as refracted light 328. The refracted light 328 results in a reduction in intensity of the internally reflected light beam 322. The detector 324 detects this reduction in intensity of light. A drop in intensity of light monitored by the light detector 324 is attributable to the presence of contamination 326 on the windshield 304.

[0165] The noise filter 329 filters out any light detected by the detector 324 attributable to other sources than the light source 320. The locating module 344 provides a two dimensional coordinate of the contamination 326 based on which of the detectors 324 have detected the contamination. This coordinate will distinguish between the interior and the exterior of the windshield 304 using the same approach since each emitter 320 can be configured to direct light either down and interior or exterior side of the IRR only. Using this coordinate, the control module 352 passes a voltage to one of the active heating zones 356 corresponding to the location where contamination has been detected.

[0166] When the detectors 324 experience an intensity of the received light returning to expected levels, the control module 352 determines that contamination 326 has cleared. The termination module 353 reduces the voltage across the heating element 354 to zero Volts. The temperature of the heating element 354 reduces accordingly.

[0167] There are various energy efficiencies in using this system since heating the windshield 304 has been made automatic in response to detecting any contamination 326 rather than letting the contamination 326 propagate to a point which might affect the driver's visibility. In addition, heating only an area of the windshield 304 corresponding to the location of contamination 326 is more energy efficient compared to a case where the entire windshield 304 is heated even when contamination 326 is localised.

[0168] Various other alternative embodiments are also possible within the scope of the appended claims. A fourth embodiment of the invention will now be described. Those features in common with the previous third embodiment are labelled with like reference numerals.

[0169] In this alternative embodiment, the windshield monitoring system is the same as the previously described third embodiment and so is not described in any further detail here.

[0170] With reference to FIG. 13, the windshield clearing system 450 of the alternative fourth embodiment includes the control module 352 having a termination module 353 installed therewith. The windshield clearing system also includes a windshield wiper system 454. The windshield wiper system 454 includes a motor 456 powering a wiper blade 458.

[0171] There are two wiper arms 458 shown in FIG. 13, however this may be reduced depending on the windshield incorporating the windshield clearing system 450. The wiper arms 458 are of conventional design incorporating being coupled to the motor 456 in a known manner. The wiper arms 458 each support a wiper blade. The wiper blade is made from rubber and is arranged to contact the exterior surface of the windshield 304.

[0172] There are two motors 456 shown in FIG. 13, each for powering a wiper arm 458. However, other configurations may be employed such as a single motor 456 driving a common linkage attached to both wiper arms 458. The motor 456 is arranged to rotate the wipers arm 458 back and forth over the exterior surface of the windshield 304 in a rotary fashion. The motor 456 can be configured to operate at several speeds.

[0173] In one mode of operation, when the windshield monitoring system (FIG. 12) detects exterior surface contamination on the windshield 304, the control module 352 (FIG. 13) configures the motors 456 to rotate the wiper arms 458 over the windshield. The wiper blades clear the windshield 304 by wiping away water. Once the windshield monitoring system (FIG. 12) ceases to detect the presence of water on the windshield 304, the termination module 353 (FIG. 13) commands the motors to terminate stop, after a cycle has been completed.

[0174] In another mode of operation, when the locating module 344 (FIG. 9) has detected localised contamination, the controller 352 (FIG. 13) will configure the motors 456 to move the wiper arms 458 to the area where contamination has been detected. Next, the motor 456 will move the wiper arm 458 back and forth over the contamination. Again, wiping will terminate once the windshield monitoring system ceases to detect contamination.

[0175] This alternative windshield clearing system has been described with reference to water based contamination. However, other contaminants such as dirt can be cleared in this way too by wiping away the dirt using the wiper blades. The wiper cycle can be a wash/wipe cycle if the contamination remains after an acceptable period of time. That said, some contaminants such as windshield cracks may cause false triggers. In this case, the termination module 353 over-rides the control module 352 after a pre-determined time period to save energy. If a predefined number of false triggers occur then the control module 352 is arranged to emit an indication to have the windshield 304 checked. The indication can be used on the vehicle 300 or off-line during manufacture or maintenance inspection. Doing so will allow the windshield to be checked since such reoccurrences may be due to cracks in the windshield 304. If the windshield 304 is found to cracked, then the windshield 304 can be replaced.

[0176] It will be appreciated that in addition, or as an alternative to clearing the interior of the windshield 304 using electrically conductive heating elements, the windshield clearing system may be arranged to generate a control signal for communication to a vehicle based heating ventilation and air conditioning (HVAC) unit comprising an air blower. The HVAC unit is arranged to condition the air in the vehicle cabin. When contamination of the interior surface of the windshield is detected, the windshield clearing system generates a signal indicative of the location and severity of detected water based contamination on the interior surface of the windshield. In response to this signal, a fan or blower located in the vehicle HVAC unit may be activated, directing moving air across the interior surface of the windshield to accelerate clearing. Depending on detected ambient conditions, such as cabin air temperature and humidity and outside air temperature and humidity, the HVAC unit blower may be used in addition to the heating elements located on the windshield 304. In this way, the termination module 353, as described above, may also have the authority to terminate an action of the HVAC unit that had been previously requested in response to a detected water based contamination on the windshield.