GB2557251A - Apparatus and method for detecting moisture on a substrate - Google Patents

Apparatus and method for detecting moisture on a substrate Download PDF

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Publication number
GB2557251A
GB2557251A GB1620457.0A GB201620457A GB2557251A GB 2557251 A GB2557251 A GB 2557251A GB 201620457 A GB201620457 A GB 201620457A GB 2557251 A GB2557251 A GB 2557251A
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United Kingdom
Prior art keywords
heating element
moisture
substrate
windscreen
voltage
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB1620457.0A
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GB201620457D0 (en
Inventor
Boyd Robin
John Greenwood Jeremy
Clarke Chris
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Jaguar Land Rover Ltd
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Jaguar Land Rover Ltd
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Filing date
Publication date
Application filed by Jaguar Land Rover Ltd filed Critical Jaguar Land Rover Ltd
Priority to GB1620457.0A priority Critical patent/GB2557251A/en
Publication of GB201620457D0 publication Critical patent/GB201620457D0/en
Publication of GB2557251A publication Critical patent/GB2557251A/en
Withdrawn legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60S—SERVICING, CLEANING, REPAIRING, SUPPORTING, LIFTING, OR MANOEUVRING OF VEHICLES, NOT OTHERWISE PROVIDED FOR
    • B60S1/00—Cleaning of vehicles
    • B60S1/02—Cleaning windscreens, windows or optical devices
    • B60S1/04—Wipers or the like, e.g. scrapers
    • B60S1/06—Wipers or the like, e.g. scrapers characterised by the drive
    • B60S1/08—Wipers or the like, e.g. scrapers characterised by the drive electrically driven
    • B60S1/0818—Wipers or the like, e.g. scrapers characterised by the drive electrically driven including control systems responsive to external conditions, e.g. by detection of moisture, dirt or the like
    • B60S1/0822—Wipers or the like, e.g. scrapers characterised by the drive electrically driven including control systems responsive to external conditions, e.g. by detection of moisture, dirt or the like characterized by the arrangement or type of detection means
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60S—SERVICING, CLEANING, REPAIRING, SUPPORTING, LIFTING, OR MANOEUVRING OF VEHICLES, NOT OTHERWISE PROVIDED FOR
    • B60S1/00—Cleaning of vehicles
    • B60S1/02—Cleaning windscreens, windows or optical devices
    • B60S1/04—Wipers or the like, e.g. scrapers
    • B60S1/06—Wipers or the like, e.g. scrapers characterised by the drive
    • B60S1/08—Wipers or the like, e.g. scrapers characterised by the drive electrically driven
    • B60S1/0818—Wipers or the like, e.g. scrapers characterised by the drive electrically driven including control systems responsive to external conditions, e.g. by detection of moisture, dirt or the like
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60S—SERVICING, CLEANING, REPAIRING, SUPPORTING, LIFTING, OR MANOEUVRING OF VEHICLES, NOT OTHERWISE PROVIDED FOR
    • B60S1/00—Cleaning of vehicles
    • B60S1/02—Cleaning windscreens, windows or optical devices
    • B60S1/04—Wipers or the like, e.g. scrapers
    • B60S1/06—Wipers or the like, e.g. scrapers characterised by the drive
    • B60S1/08—Wipers or the like, e.g. scrapers characterised by the drive electrically driven
    • B60S1/0818—Wipers or the like, e.g. scrapers characterised by the drive electrically driven including control systems responsive to external conditions, e.g. by detection of moisture, dirt or the like
    • B60S1/0822—Wipers or the like, e.g. scrapers characterised by the drive electrically driven including control systems responsive to external conditions, e.g. by detection of moisture, dirt or the like characterized by the arrangement or type of detection means
    • B60S1/0825—Capacitive rain sensor
    • B60S1/0829—Oscillator-resonator rain sensor
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/22—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance
    • G01N27/223—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance for determining moisture content, e.g. humidity
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B3/00—Ohmic-resistance heating
    • H05B3/84—Heating arrangements specially adapted for transparent or reflecting areas, e.g. for demisting or de-icing windows, mirrors or vehicle windshields
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B3/00—Ohmic-resistance heating
    • H05B3/84—Heating arrangements specially adapted for transparent or reflecting areas, e.g. for demisting or de-icing windows, mirrors or vehicle windshields
    • H05B3/86—Heating arrangements specially adapted for transparent or reflecting areas, e.g. for demisting or de-icing windows, mirrors or vehicle windshields the heating conductors being embedded in the transparent or reflecting material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60S—SERVICING, CLEANING, REPAIRING, SUPPORTING, LIFTING, OR MANOEUVRING OF VEHICLES, NOT OTHERWISE PROVIDED FOR
    • B60S1/00—Cleaning of vehicles
    • B60S1/02—Cleaning windscreens, windows or optical devices
    • B60S1/023—Cleaning windscreens, windows or optical devices including defroster or demisting means

Abstract

Embodiments of the present invention provide systems for detecting the presence of moisture on a glass substrate or windscreen (10) associated with a heating element (16). Such a system may comprise a voltage source configured to provide a temporally varying voltage signal across said heating element (16), a sensing means, a voltmeter (24), which is arranged to detect a response of the heating element to the said voltage signal and to produce an output in dependence on the said response, and control means communicably coupled to the said sensing means. The control means may be arranged to determine a presence of moisture on the substrate in dependence on the output from the sensing means. Such systems may be particularly useful within automatic windscreen wiper systems or auto-demist systems of vehicles.

Description

(54) Title ofthe Invention: Apparatus and method for detecting moisture on a substrate Abstract Title: Apparatus and Method for Detecting Moisture on a Substrate (57) Embodiments ofthe present invention provide systems for detecting the presence of moisture on a glass substrate or windscreen (10) associated with a heating element (16). Such a system may comprise a voltage source configured to provide a temporally varying voltage signal across said heating element (16), a sensing means, a voltmeter (24), which is arranged to detect a response ofthe heating element to the said voltage signal and to produce an output in dependence on the said response, and control means communicably coupled to the said sensing means.
The control means may be arranged to determine a presence of moisture on the substrate in dependence on the output from the sensing means. Such systems may be particularly useful within automatic windscreen wiper systems or auto-demist systems of vehicles.
Figure GB2557251A_D0001
At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.
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Figure GB2557251A_D0002
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Figure GB2557251A_D0005
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Figure GB2557251A_D0006
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Figure GB2557251A_D0008
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Figure GB2557251A_D0012
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Figure GB2557251A_D0013
Record the state of switch 20'
Determine the temperature of heating elements 16
OO
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414.
Load data indicative of the ringing frequency for heater 11 or the settling time of the voltage signal measured across the heater 11 in a dry windscreen 10 at the determined temperature.
5
Change the state of switch 20'
Determine the ringing frequency or the settling time of the voltage of the heater 11
416
Figure GB2557251A_D0014
Moisture present - switch on windscreen wipers 34
Moisture not present -- switch off windscreen wipers 34
422.
424.
Return switch 20 to recorded state
Wait 5 seconds
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Figure GB2557251A_D0015
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Figure GB2557251A_D0016
Figure GB2557251A_D0017
Apparatus and Method for Detecting Moisture on a Substrate
TECHNICAL FIELD
Aspects of the invention relate to a system for detecting moisture on a substrate, to a method of detecting moisture on a substrate, and to a vehicle.
BACKGROUND
Under certain circumstances it can be desirable to detect the presence of moisture on a substrate such as glass or another impermeable substrate. For example, many modern vehicles are provided with automatic windscreen wiper systems that are arranged to activate whenever moisture is detected on the windscreen. Such systems are provided with a moisture sensor that is arranged to detect moisture on the windscreen and produce an output indicative of the presence of moisture on the windscreen. The windscreen wipers are then switched on in response to the output indicative of the presence of moisture on the windscreen.
Existing automatic windscreen wiper systems typically use optical sensors that detect changes in the reflective or refractive characteristics of the outer surface of the windscreen to infer the presence of moisture on the outer surface of the windscreen, which will most likely be the result of rain or other precipitation. A disadvantage of such sensors is that they are typically only able to detect moisture on a relatively small area of the windscreen. This is not usually problematic, as precipitation will generally cause the entire windscreen to become wet to a generally similar extent. However, it can lead to the system activating the windscreen wipers when it is not strictly necessary if a small amount of moisture happens to land on the area that the sensor is arranged to detect moisture on, which can lead to driver confusion or annoyance. The problem could be overcome by providing a plurality of sensors and programming the system to only actuate the windscreen wipers when more than one of the sensors has detected moisture on the windscreen, but this would increase the cost and complexity of the system.
A related situation in which it is desirable to detect moisture on glass is as part of an auto-demist system of a vehicle. Auto-demist systems are similar to automatic windscreen wipers, but they are arranged to detect moisture on the inner surface of the windscreen, and to automatically turn on a demister device such as a fan in response to a detection of moisture on the inside of the windscreen. Similar sensors may be used in automatic windscreen wiper systems and auto-demist systems.
It is an object of embodiments of the invention to at least mitigate one or more of the problems of the prior art.
SUMMARY OF THE INVENTION
According to an aspect of the invention for which protection is sought there is provided a system for detecting the presence of moisture on a substrate associated with a heating element, the system comprising:
a voltage source configured to provide a temporally varying voltage signal across said heating element;
sensing means arranged to detect a response of the heating element to said voltage signal and to produce an output in dependence on said response; and control means communicably coupled to said sensing means, the control means being arranged to determine a presence of moisture on the substrate in dependence on the output from the sensing means. The substrate may be a glass substrate or another impermeable substrate. Optionally, the substrate is substantially transparent. The heating element may be a resistive heating element. The heating element may be embedded within the substrate and distributed over a large area. Accordingly, the response of the heating element to the voltage signal may depend on the state of a large proportion of the area of the substrate. The system is therefore operable to determine whether or not there is moisture on the substrate based on an output that is affected by the state of a large proportion of the area of the substrate.
Another advantage of the system described above is that it may obviate the need for an optical sensor to be provided as part of an automatic windscreen wiper system, which may reduce the overall cost of such a system.
The sensing means may be a sensor. The control means may be a controller, which controller may comprise a processor communicably coupled to an electronic memory.
Optionally, the controller is configured to cause a wiper associated with the substrate to be activated upon determining that moisture is present on the substrate. The controller may be configured to select a speed setting of the wiper in dependence on the output from the sensing means. This may provide an automatic windscreen wiper system.
Further optionally, the controller may be configured to cause a demister associated with the substrate to be activated upon determining that moisture is present on the substrate. This may provide an auto-demist system.
In an embodiment said controller is further configured to determine a temperature of the heating element, and said determination of whether or not moisture is present on the substrate is made in dependence on said temperature. This may improve the accuracy of the system, as it allows the controller to correct for changes in temperature. This can be important, as the response of the heating element to the temporally varying voltage signal may depend on the temperature of the heating element as well as the presence of moisture on the substrate.
According to another embodiment said resistive heating element comprises a plurality of wires electrically connected in parallel and embedded within said substrate. The heating element may be a heater of a windscreen, optionally a front windscreen and/or a rear screen, of a vehicle.
Optionally, the voltage source is configured to produce a temporally varying voltage at a plurality of different frequencies. For example, the voltage source may comprise a voltage controlled oscillator. Such a voltage controlled oscillator may be operable to “sweep” across a range of frequencies. Advantageously, this may allow the sensing means to detect a response indicative of a resonant frequency of a circuit including the heating element. The controller may be arranged to determine that moisture is present on the substrate if the output indicates that the resonant frequency is not within a predetermined range. The predetermined range may be determined in dependence on the instantaneous temperature of the heating element.
Optionally, the heating element may comprise a first heating element and a second heating element, wherein the voltage source is operable to apply a voltage across said first heating element without applying a voltage across said second heating element. The sensing means may be arranged to detect an output indicative of the inductive coupling between the first heating element and the second heating element.
In another embodiment the voltage source comprises a DC voltage source in combination with a switch. The sensing means may be arranged to detect an output indicative of the response of the heating element to a step change in the voltage applied thereacross. Optionally, the output indicative of the response of the heating element to a step change in the voltage applied thereacross comprises an output indicative of the ringing frequency and/or the settling time of the voltage signal across the heating element after a step change in the voltage applied across the heating element.
Optionally, the sensing means comprises a voltmeter. The voltmeter may be positioned in parallel with the heater. This may allow the voltmeter to determine the voltage drop across the heater. Optionally, the voltmeter may be coupled to a frequency analyser. The frequency analyser may be configured to provide a signal indicative of frequency domain characteristics of the voltage signal to the control means. However, it will be understood that in some embodiments the control means itself may analyse the voltage signal to determine frequency domain characteristics of the voltage signal.
In an embodiment, the system comprises the wiper.
In an embodiment the substrate is a windscreen. In other embodiments the substrate may be a sunroof, a rear screen, a side window, a drop glass, an externally mounted side mirror such as a wing mirror or door mirror, an internal rear view mirror, camera lens or a headlamp or other light unit, provided such substrates are associated with a heating element.
According to another aspect of the invention for which protection is sought there is provided a method of detecting the presence of moisture on a substrate associated with a heating element, comprising:
providing a temporally varying voltage signal across said heating element; detecting a response of the heating element to said voltage signal; providing an output in dependence on said response; and determining a presence of moisture on the substrate in dependence on the output.
Optionally, the method, comprises causing a wiper associated with the substrate to be activated upon determining that moisture is present on the substrate.
In an embodiment, the method comprised selecting a speed setting of the wiper in dependence on the output from the sensing means.
According to another aspect of the invention for which protection is sought there is provided a computer program product executable on a processor so as to implement a method as described above.
According to another aspect of the invention for which protection is sought there is provided a non-transitory computer readable medium carrying computer readable code which when executed causes a vehicle to carry out the a as described above.
According to another aspect of the invention for which protection is sought there is provided a processor arranged to implement a method or a computer program product as described above.
According to another aspect of the invention for which protection is sought there is provided a vehicle comprising a system, a computer program product, a nontransitory computer readable medium or a processor as described above.
Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described by way of example only, with reference to the accompanying figures, in which:
Figures 1A and 1B show two different prior art heating systems for windscreens;
Figure 2A shows a schematic diagram of a system for detecting the presence of moisture on a windscreen according to an embodiment of the present invention;
Figure 2B shows a RLC circuit that is approximately equivalent to the circuit shown in figure 2A;
Figure 3 is a flow chart illustrating a method of determining whether or not moisture is present on a windscreen according to an embodiment of the invention;
Figure 4 shows a comparison between a frequency response curve obtained for a dry windscreen and a frequency response curve obtained for a wet windscreen according to an embodiment of the invention;
Figure 5 shows a schematic diagram of a system that can be used for detecting the presence of moisture on a windscreen according to another embodiment of the present invention;
Figure 6 is a flow chart illustrating another method of determining whether moisture is present on a windscreen according to an embodiment of the invention;
Figure 7 shows a schematic diagram of a system that can be used for detecting the presence of moisture on a windscreen according to another embodiment of the present invention;
Figure 8 shows a flow chart illustrating another method of determining whether or not moisture is present on a windscreen according to an embodiment of the invention;
Figure 9 shows a comparison between the ringing obtained after a step change in the voltage applied to a heater in a dry windscreen and the ringing obtained after a step change in the voltage applied to a heater in a wet windscreen according to an embodiment of the invention; and
Figure 10 shows a vehicle that can incorporate a system according to embodiments of the present invention.
DETAILED DESCRIPTION
Modern vehicles are often provided with heated windscreens that are arranged to heat the windscreen to remove ice or condensation from the windscreen. A schematic representation of such a windscreen is shown in figure 1.
Figure 1A shows a front windscreen 10, which may be the windscreen of a vehicle 600, having a heater 11 comprising a plurality of thin wire resistive heating elements 16 and two conductive strips 12, 14 embedded in the windscreen. Each of the wires 16 is connected at one end to conducting strip 12 and at the other end to conducting strip 14. When heating of the windscreen is required conducting strips 12, 14 are connected to respective terminals of a DC voltage source such as a 12V battery of the vehicle, thereby causing an electric current to flow through the wire heating elements 16. It will be appreciated by one skilled in the art that whilst the following example describes a substrate taking the form of a front windscreen 10, this may additionally or alternatively be any transparent member of a vehicle that is prone to becoming wet in normal use to the detriment of its function, and for which a wiper and or a demisting system may be employed to maintain useful function. Example of such transparent members include: a rear screen, a sunroof, a side window, a drop glass, an externally mounted side mirror such as a wing mirror or door mirror, an internal rear view mirror, camera lens or a headlamp assembly or other externally mounted lighting unit.
The wire heating elements 16 are typically sufficiently thin that they do not obscure the view through the windscreen, and they are generally placed close enough together to allow the combination of the heating elements to heat all of a substantially continuous region of the windscreen. In use, only the region of the windscreen 10 between lines A and B may be visible. This may prevent the conducting strips 12, 14 from obscuring a driver’s view through the windscreen.
Although the embodiment shown in figure 1A shows all of the wire heating elements 16 connected to the same conducting strips 12, 14, it will be understood that it is also possible to provide two separate heaters 1Γ, 11 in different regions of the windscreen 10. For example, it is known to connect all of the heating elements 16 in a first half of the windscreen to a first pair of conducting strips 12', 14' and to connect all of the heating elements in a second half of the windscreen to a second pair of heating elements 12, 14, as shown in figure 1B.
Figure 2A shows a circuit incorporating a heating system as shown in figure 1A that can be used to detect the presence of moisture on a windscreen 10. In the circuit shown in figure 2A the connection of the heating elements 16 to a DC voltage source is controlled by switch 20. An AC voltage can also be applied across the heating elements 16 by voltage controlled oscillator (VCO) 22. Capacitor 26 is provided in series with VCO 22 to prevent a direct current flowing through the VCO 22 when switch 20 is closed. A sensing means comprising a voltmeter 24 is also provided in parallel with the heating elements 16, and both the voltmeter 24 and the VCO 22 are communicably coupled with a control means, which comprises a controller 28 having a processor 30 communicably coupled with an electronic memory 32.
The present inventors have recognised that the heaters 11, 1Γ, 11 shown in figures 1A and 1B can provide significant capacitance and inductance in addition to the combined resistance of the heating elements and the conductive strips. This may be a result of the close positioning of the wire heating elements. Under normal operation with the conducting strips connected to a DC voltage source this capacitance and inductance has substantially no effect, as the system operates in a generally steady state.
As heater 11 may provide significant inductance and capacitance in addition to its resistance, the behaviour of the heater 11 in the circuit shown in figure 2A may be approximated by an RLC circuit such as the one shown in figure 2B. Figure 2B shows a resistor 11R arranged in series with an inductor 11L, and a capacitor 11C arranged in parallel with the inductor 11L and the resistor 11R. It will be understood that the behaviour of the heater 11 could alternatively be approximated by other arrangements of RLC circuit.
When a DC voltage is applied across the heater 11 by closing switch 20 the contribution of the capacitance 11C and inductance 11L is negligible after the initial switching on of the voltage, so the circuit behaves as it would if the heater 11 provided only a resistance after an initial settling period, which may be relatively short.
The present inventors have also recognised that the capacitance 11C provided by the heater 11 may change when moisture is present on the windscreen 10, as the presence of moisture causes a change in the dielectric properties of the heating elements 16. The system shown in figure 2A may be used to determine whether or not moisture is present on the windscreen 10 by applying a temporally varying voltage signal across the heater 11 using the VCO 22. The response of the heater 11 to the temporally varying voltage signal is then detected by voltmeter 24, which then produces an output in dependence on the response of the heater 11 to the temporally varying voltage signal. The controller 28 is communicably coupled with the voltmeter 24 and is arranged to determine whether or not moisture is present on the windscreen 10 in dependence on the output from the voltmeter 24. The process by which the system shown in figure 2A can be used to determine whether or not moisture is present on a substrate such as the vehicle windscreen 10 or other transparent member will be described in more detail with reference to figure 3.
Figure 3 shows a method 100 by which the system shown in figure 2A may be used to detect moisture on a windscreen 10. The method is initiated at step 102 and immediately proceeds to step 104, in which the system reads the current, that is to say the present state of switch 20 and records that state in electronic memory 32. The method then proceeds to step 106, in which the system determines the temperature of the heating elements 16. This may be achieved by closing switch 20 (if it was not already closed) and then determining the current flowing through the heating elements 16 by reference to an output from ammeter 36. Because the voltage that is applied across the heating elements 16 is known (12V in the illustrated embodiment) and the DC resistance of the voltmeter 24 and the capacitor 26 are likely to both be significantly higher than that of the heating elements 16, it is possible to determine the instantaneous resistance of the heating elements 16 from the measured electrical current value using the relationship R=V/I. The resistance of thin wire heating elements 16 is known to vary in dependence on the temperature of the heating elements, so the calculated resistance may be used to determine the temperature of the heating elements 16 using an empirically derived formula or lookup table.
Once the temperature has been determined, the method proceeds to step 108, in which the controller 28 loads a frequency response curve 200 (as shown in figure 4) corresponding to a dry windscreen at the determined temperature from electronic memory 32. It will be understood that a finite number of frequency response curves for different temperatures may be stored on electronic memory 32, and the controller 28 may be arranged to interpolate between stored frequency response curves if the determined temperature is between temperatures for which frequency response curves are stored. Furthermore, it will be understood that in some embodiments it may be unnecessary to actually calculate the temperature of the heating elements 16, as the measured electrical current values may be taken to be indicative of the temperature, and the stored frequency response curves may be associated with different current values.
The method then proceeds to step 110, in which switch 20 is opened. This prevents the DC voltage from affecting the readings obtained using voltmeter 24 in subsequent steps. The method then proceeds to step 112, in which the controller 28 applies a single period of a saw tooth waveform to the VCO 22. The saw tooth waveform starts at a voltage of 0V and then the voltage increases a linear rate until a maximum voltage value is reached, at which point the voltage drops back to 0V substantially immediately. This causes the VCO 22 to produce an oscillating voltage signal with a linearly increasing frequency until the voltage applied by the controller drops back to zero, at which point the VCO ceases to produce an oscillating voltage signal. Whilst the oscillating voltage signal is being applied by the VCO the controller 28 monitors the output of voltmeter 24 and then determines a frequency response curve 202 of the heater 16 in step 114.
Once the frequency response curve has been determined it is compared to the frequency response curve for a dry windscreen at equivalent temperature in step 116. Figure 4 illustrates frequency response curves 200, 202 showing the voltage amplitude V as measured by voltmeter 24 against the frequency f of the voltage signal produced by VCO 22. Frequency response curve 200 corresponds to that obtained for a particular windscreen under dry conditions. Such a frequency response curve may be loaded into the memory 32 during a calibration stage of manufacture of a vehicle incorporating a system according to the present invention. Figure 4 also illustrates a frequency response curve 202 that may be obtained during step 114 of the method illustrated in figure 3. Frequency response curve 200 shows a resonant frequency ti, whilst frequency response curve 202 shows a resonant frequency f2. The difference between and f2 is represented by Δί.
In some embodiments the frequency response curve may be considered to differ from the frequency response curve for a dry windscreen if the difference Δί is greater than a predetermined amount. The magnitude of the difference in resonant frequency that is required to make a positive determination that there is moisture on the windscreen may be determined empirically based on the observed resonant frequencies for a dry windscreen and for the same windscreen having an amount of moisture thereon that would begin to interfere with a driver’s vision.
If a determination that the frequency response curve differs from the frequency response curve for a dry windscreen is made in step 116 then the controller 28 determines that moisture is present on the windscreen 10 and the method proceeds to step 118, in which the windscreen wipers 34 are activated by the controller 28 (if they were previously switched off or otherwise not active at the time). Alternatively, if a determination that the frequency response curve does not differ from the frequency response curve for a dry windscreen is made in step 116, then the controller 28 determines that moisture is not present on the windscreen 10 and the method proceeds to step 120, in which the windscreen wipers are switched off or otherwise deactivated (if they were previously switched on).
In some embodiments the windscreen wipers may have a plurality of speed settings or modes (including a single wipe or flick-wipe setting or mode) and, if a determination is made that there is moisture on the windscreen and the windscreen wipers are to be activated then the controller may select an appropriate speed setting or mode in dependence on the difference Δί between the resonant frequency for the windscreen in a dry state fi and the resonant frequency f2 as determined from the frequency response curve obtained in step 114. Furthermore, if the windscreen wipers are currently switched on and the system determines that the windscreen still has moisture on it then the controller 28 may change the speed of the windscreen wipers in response to a change in the difference Δί between the resonant frequency for the windscreen in a dry state fi and the resonant frequency f2 as determined from the frequency response curve obtained in step 114.
After step 118 or step 120 the method proceeds to step 122, in which the switch 20 is returned to the state recorded in step 104. It will be understood that in some embodiments steps 106 and 122 may be omitted, and instead the controller 28 may be arranged to detect the position of switch 20 and, if the switch 20 is open, correct for the effect of the DC voltage when determining a frequency response curve in dependence on the output from the voltmeter 24. A low-pass filter may be provided to prevent any high frequency noise from the DC voltage source from affecting the measurement of the frequency response curve 202.
A five-second wait is introduced in step 124 to prevent the method 100 from causing the switch 20 to be open for too high a proportion of the time, which would interfere with normal operation of the heater 11. After the five second wait the method returns to step 104 and is repeated.
Figure 5 shows a system that can be used to detect moisture on a glass substrate such as a windscreen 10 having a first heater 11' and a second heater 11 associated therewith. Components in figure 5 that are similar to corresponding components in figure 2A are indicated by the same reference numerals.
The system shown in figure 5 is operable to measure changes in the strength of the inductive coupling between the first and second heaters 1Γ, 11, each of which can be energised independently of the other. Such changes in inductive coupling may be indicative of the presence of moisture on the windscreen 10. Operation of the system shown in figure 5 will be described in further detail with respect to the flow chart in figure 6, which shows a method 300 by which the system shown in figure 5 can be operated.
The method is initiated at step 302 and immediately proceeds to step 304, in which the system reads the state of switch 20 at that time and records that state in electronic memory 32. The method then proceeds to step 306, in which the system determines the temperature of the heating elements 16. This may be achieved by closing switch 20 (if it was not already closed) and then determining the electrical current flowing through the heating elements 16 by reference to an output from ammeter 36. As described above, the electric current flowing through the heaters may be indicative of the temperature of the heaters.
Once the temperature has been determined the method proceeds to step 308, in which the controller 28 loads data indicative of the inductive coupling between the first and second heaters 1 T, 11 in a dry windscreen at the determined temperature from electronic memory 32. This data may comprise a maximum induced voltage in the second heater 11 when an oscillatory voltage signal of a particular magnitude and frequency is applied across the first heater 1T. The skilled person will recognise that alternative data indicative of the inductive coupling between the first and second heaters 1Γ, 11 could also be used.
It will be understood that data indicative of the inductive coupling between the first and second heaters 1Γ, 11” in a dry windscreen at a finite number of different temperatures may be stored on electronic memory 32, and the controller 28 may be arranged to interpolate between data points if the determined temperature is between temperatures for which frequency response curves are stored.
The method then proceeds to step 310, in which the switch 20 is opened. This prevents the DC voltage from affecting the readings obtained using voltmeter 40 in subsequent steps. The method then proceeds to step 312, in which the controller 28 applies a constant voltage to the VCO 22. This causes the VCO to provide an AC voltage signal of constant magnitude and frequency, which magnitude and frequency may be equivalent to the magnitude and frequency of the signal used when obtaining the data indicative of the inductive coupling between the first and second heaters 1Γ, 11” in a dry windscreen. Whilst the oscillating voltage signal is being applied by the VCO the controller 28 monitors the output of voltmeter 40 and records data indicative of the inductive coupling between the first heater 11' and the second heater 11. The recorded data may comprise the maximum induced voltage in the second heater 11 or the root mean square of the voltage signal observed in the second heater 11 during application of the oscillatory voltage signal to the first heater 1Γ. It will be understood that other data indicative of the inductive coupling could also be used.
Once the data indicative of the inductive coupling between the heaters has been obtained at step 314, it is compared to the corresponding data for a dry windscreen at equivalent temperature that was loaded in step 308. In some embodiments the inductive coupling between the heaters may be considered to differ from the corresponding inductive coupling for a dry windscreen if the maximum induced voltage in the second heater 11 differs from the maximum induced voltage observed for a dry windscreen by more than a predetermined amount. The magnitude of the difference in maximum induced voltage that is required to make a positive determination that there is moisture on the windscreen may be determined empirically based on the observed induced voltages for a dry windscreen and for the same windscreen having an amount of moisture thereon that would begin to interfere with a driver’s vision.
If a determination that the inductive coupling differs from the inductive coupling for a dry windscreen is made in step 316 then the controller 28 determines that moisture is present on the windscreen 10 and the method proceeds to step 318, in which the windscreen wipers 34 are switched on by the controller 28 (if they were previously switched off or otherwise not active at the time). Alternatively, if a determination that the inductive coupling does not differ from the inductive coupling for a dry windscreen is made in step 316 then the controller 28 determines that moisture is not present on the windscreen 10 and the method proceeds to step 320, in which the windscreen wipers are switched off (if they were previously switched on).
In some embodiments the speed setting of the windscreen wipers may be selected in dependence on the magnitude of the difference between the data indicative of the current inductive coupling and the data indicative of the inductive coupling for a dry windscreen.
After step 318 or step 320 the method proceeds to step 322, in which the switch 20 is returned to the state recorded in step 304. It will be understood that in some embodiments steps 306 and 322 may be omitted, and instead the controller 28 may be arranged to detect the position of the switch 20 and, if the switch 20 is open, correct for the effect of the DC voltage when determining a the inductive coupling between the first and second heaters 1Γ, 11 in dependence on the output from the voltmeter 40. A low-pass filter may be provided to prevent any high frequency noise from the DC voltage source from affecting the measurements taken during step 314.
A five-second wait is introduced in step 324 to prevent the method 300 from causing the switch 20 to be open for too high a proportion of the time. After the five second wait the method returns to step 304 and is repeated.
Figure 7 shows another system that can be used to detect moisture on a glass substrate such as a windscreen 10 having a heater 11 embedded therein. Components in figure 7 that are similar to corresponding components in figure 2A are indicated by the same reference numerals.
The system shown in figure 7 is operable to detect changes in the response of the heater 11 to step changes in the voltage applied across the heater. Such changes in the response may be indicative of the presence of moisture on the windscreen 10. Operation of the system shown in figure 7 will be described in more detail with respect to the flow chart shown in figure 8, which shows a method 400 by which the system shown in figure 7 can be operated.
The method is initiated at step 402 and immediately proceeds to step 404, in which the system reads the state of switch 20' at that time and records that state in electronic memory 32. The switch 20' may be the same as the switch 20 used in the embodiments shown in figures 2A and 5. However, as will become apparent from the following description, it may be desirable to use a switch having a particularly fast and consistent response time for the present embodiment, as this may help to ensure that changes in the response of the heater 11 to step changes in the voltage applied across it are the result of changes in the dielectric properties of the heater 11 as a result of the presence of moisture, and not the result of inconsistencies in the operation of the switch.
After step 404 the method then proceeds to step 406, in which the system determines the temperature of the heating elements 16. This may be achieved by closing switch 20' (if it was not already closed) and then determining the current flowing through the heating elements 16 by reference to an output from ammeter 36. As described above, the current flowing through the heaters may be indicative of the temperature of the heaters.
Once the temperature has been determined the method proceeds to step 408, in which the controller 28 loads data indicative of the response of the heater 11 to a step change in voltage in a dry windscreen at the determined temperature from electronic memory 32. This data may comprise the ringing frequency or the settling time of the voltage signal measured across the heater 11 in response to a given step change in the voltage applied across the heater.
The method then proceeds to step 410, in which the state of switch 20' is changed. In the description of present embodiment the change will be from an open state to a closed state, although the skilled person will understand that the change could alternatively be from a closed state to an open state. Opening the switch 20' causes a step change in the voltage across the heater 11. As the switch 20' is opened the controller 28 monitors the output of voltmeter 24 and records data indicative of the response of the heater 11 to a step change in voltage. For example, the recorded data may be indicative of the ringing frequency or the settling time of the voltage signal after the step change is applied. It will be understood that other data indicative of the response of the heater 11 to a step change in the voltage applied thereacross could also be used.
Once the data indicative of the response of the heater 11 to a step change in the voltage applied thereacross is obtained it is compared to the corresponding data for a dry windscreen at equivalent temperature that was loaded in step 408. In some embodiments the data indicative of the response of the heater 11 to a step change in the voltage applied thereacross may be considered to differ from the corresponding inductive coupling for a dry windscreen if the observed ringing frequency differs from the ringing frequency for a dry windscreen by more than a predetermined amount. The magnitude of the difference that is required to make a positive determination that there is moisture on the windscreen may be determined empirically based on the observed ringing frequencies for a dry windscreen and for the same windscreen having an amount of moisture thereon that would begin to interfere with a driver’s vision.
If a determination that the response of the heater 11 to a step change in the voltage applied thereacross differs from that for a dry windscreen is made in step 416 then the controller 28 determines that moisture is present on the windscreen 10 and the method proceeds to step 418, in which the windscreen wipers 34 are switched on by the controller 28 (if they were previously switched off). Alternatively, if a determination that the response of the heater 11 to a step change in the voltage applied thereacross does not differ from the that for a dry windscreen is made in step 416 then the controller 28 determines that moisture is not present on the windscreen and the method proceeds to step 420, in which the windscreen wipers are switched off (if they were previously switched on).
In some embodiments the speed setting or mode setting of the windscreen wipers may be selected in dependence on the magnitude of the difference between the ringing frequency, settling time, or other data indicative of the response of the heater to a step change in the voltage applied thereacross and the corresponding data for a dry windscreen.
Figure 9 shows a curve 500 showing the voltage signal V measured by voltmeter 20 in the time t following a step change in voltage across a dry heater 11 from Vo to V15 which occurs at t0. Curve 502 shows the voltage signal measured by voltmeter 20 to the same step change in voltage when the windscreen 10 is wet.
As can be seen from figure 9, both curves 500, 502 show a decaying oscillation in the voltage V immediately after the step change at t0. Curve 500 has voltage peaks at time ft and t2, which peaks are separated by a time period p1; whilst curve 502 has voltage peaks at time t3 and t4, which peaks are separated by a time period p2. It will be understood that the ringing frequency of the voltage signals 500, 502 is inversely proportional to the time period of the oscillations. If p! and p2 are measured in seconds then the ringing frequency (in Hertz) of the voltage signal 500 (which corresponds to the voltage signal obtained when the windscreen is dry) is given by the expression fR1 = 1/pb and the ringing frequency (in Hertz) of the voltage signal 502 (which corresponds to the voltage signal obtained when the windscreen is wet) is given by the expression fR2 = 1/p2.
It will be understood that the presence of moisture on the windscreen 10 may have the effect of increasing the capacitance of the heater 11, and that this may have the effect of changing the ringing frequency of the voltage signal when a step change in voltage is applied across the heater 11.
Although the present invention has been described with particular reference to its application within an automatic windscreen wiper system, it will be understood that it may equally be applied to other systems. For example, it will be understood that the system may also be suitable for detecting condensation on an inside surface of a windscreen, and that upon detecting such condensation a controller as described in any of the above embodiments may be configured to cause a demister such as a blower to be activated. Additionally or alternatively, upon detecting condensation on an inside surface of a substrate such as a windscreen 10, a controller as described in any of the above embodiments may be configured to cause an auxiliary heater device, such as an auxiliary fuel burning heater or a PTC heater, to be activated.
It will be appreciated that embodiments of the present invention can be realised in the form of hardware, software or a combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape. It will be appreciated that the storage devices and storage media are embodiments of machine-readable storage that are suitable for storing a program or programs that, when executed, implement embodiments of the present invention. Accordingly, embodiments provide a program comprising code for implementing a system or method as claimed in any preceding claim and a machine readable storage storing such a program. Still further, embodiments of the present invention may be conveyed electronically via any medium such as a communication signal carried over a wired or wireless connection and embodiments suitably encompass the same.
All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.
Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. The claims should not be construed to cover merely the foregoing embodiments, but also any embodiments which fall within the scope of the claims.

Claims (25)

1. A system for detecting the presence of moisture on a substrate associated with a heating element, the system comprising:
a voltage source configured to provide a temporally varying voltage signal across said heating element;
sensing means arranged to detect a response of the heating element to said voltage signal and to produce an output in dependence on said response; and control means communicably coupled to said sensing means, the control means being arranged to determine a presence of moisture on the substrate in dependence on the output from the sensing means.
2. A system as claimed in claim 1, wherein the control means is configured to cause a wiper associated with the substrate to be activated upon determining that moisture is present on the substrate.
3. A system as claimed in claim 2, wherein the control means is configured to select a speed setting of the wiper in dependence on the output from the sensing means.
4. A system as claimed in claim 1,2, or 3, wherein said control means is further configured to determine a temperature of the heating element, and said determination of whether or not moisture is present on the substrate is made in dependence on the said temperature.
5. A system as claimed in any of claims 1 -4, wherein said heating element comprises a plurality of wires electrically connected in parallel and embedded within said substrate.
6. A system as claimed in any preceding claim, wherein the voltage source is configured to produce a temporally varying voltage at a plurality of different frequencies.
7. A system as claimed in claim 6, wherein the voltage source comprises a voltage controlled oscillator.
8. A system as claimed in any preceding claim, wherein the sensing means is arranged to detect a response indicative of a resonant frequency of a circuit including the heating element, and the control means is arranged to determine that moisture is present on the substrate if the output indicates that the resonant frequency is not within a predetermined range.
9. A system as claimed in any preceding claim, wherein the heating element comprises a first heating element and a second heating element, wherein the voltage source is operable to apply a voltage across said first heating element without applying a voltage across said second heating element.
10. A system as claimed in claim 9, wherein said sensing means is arranged to detect an output indicative of the inductive coupling between the first heating element and the second heating element.
11. A system as claimed in any preceding claim, wherein the voltage source comprises a DC voltage source in combination with a switch.
12. A system as claimed in claim 11, wherein the sensing means is arranged to detect an output indicative of the response of the heating element to a step change in the voltage applied thereacross.
13. A system as claimed in claim 12, wherein the output indicative of the response of the heating element to a step change in the voltage applied thereacross comprises an output indicative of the ringing frequency of the voltage signal across the heating element after a step change in the voltage applied across the heating element.
14. A system as claimed in any preceding claim, wherein the sensing means comprises a voltmeter.
15. A system as claimed in claim 2, or any of claims 3-14 where dependent on claim 2, wherein the system comprises said wiper.
16. A system as claimed in any preceding claim, wherein the substrate is a windscreen.
17. A controller for detecting the presence of moisture on a substrate associated with a heating element, the controller being configured to:
receive a signal indicative of a response of the heating element to a temporally varying voltage signal across the heating element; and determine a presence of moisture on the substrate in dependence on the signal.
18. A method of detecting the presence of moisture on a substrate associated with a heating element, the method comprising:
providing a temporally varying voltage signal across said heating element; detecting a response of the heating element to said voltage signal; providing an output in dependence on said response; and determining a presence of moisture on the substrate in dependence on the output.
19. A method as claimed in claim 18, comprising activating a wiper associated with the substrate upon determining that moisture is present on the substrate.
20. A method as claimed in claim 19, comprising selecting a speed setting of the wiper in dependence on the output from the sensing means.
21. A computer program product executable on a processor so as to implement the method of any of claims 18-20.
22. A non-transitory computer readable medium carrying computer readable code which when executed causes a vehicle to carry out the method of any of claims 1820.
23. A processor arranged to implement the method of any of claims 18-20, or the computer program product of claim 20.
24. A vehicle comprising a system as claimed in any of claims 1 -16, a controller as claimed in claim 17, a computer program product as claimed in claim 21, a nontransitory computer readable medium as claimed in claim 22 or a processor as claimed in claim 23.
25. A system, a method or a vehicle substantially as described herein with reference to the accompanying figures 2-10.
Intellectual
Property
Office
Application No: GB1620457.0 Examiner: Mr Charles Ellwood
GB1620457.0A 2016-12-02 2016-12-02 Apparatus and method for detecting moisture on a substrate Withdrawn GB2557251A (en)

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Application Number Priority Date Filing Date Title
GB1620457.0A GB2557251A (en) 2016-12-02 2016-12-02 Apparatus and method for detecting moisture on a substrate

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GB2557251A true GB2557251A (en) 2018-06-20

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2020002322A3 (en) * 2018-06-25 2020-02-20 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Electrical circuit, method for an electrical circuit and computer program

Citations (4)

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Publication number Priority date Publication date Assignee Title
DE4426736A1 (en) * 1994-07-28 1996-02-01 Vdo Schindling Humidity sensor for heated front or rear window of vehicle
GB2325993A (en) * 1997-06-06 1998-12-09 Bosch Gmbh Robert Controlling a windscreen or window heater using a moisture sensor
CN102438342A (en) * 2011-09-26 2012-05-02 浙江吉利汽车研究院有限公司 Vehicle window glass with heating function
GB2507060A (en) * 2012-10-17 2014-04-23 Nissan Motor Mfg Uk Ltd Window assembly

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4426736A1 (en) * 1994-07-28 1996-02-01 Vdo Schindling Humidity sensor for heated front or rear window of vehicle
GB2325993A (en) * 1997-06-06 1998-12-09 Bosch Gmbh Robert Controlling a windscreen or window heater using a moisture sensor
CN102438342A (en) * 2011-09-26 2012-05-02 浙江吉利汽车研究院有限公司 Vehicle window glass with heating function
GB2507060A (en) * 2012-10-17 2014-04-23 Nissan Motor Mfg Uk Ltd Window assembly

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2020002322A3 (en) * 2018-06-25 2020-02-20 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Electrical circuit, method for an electrical circuit and computer program

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