GB2426434A

GB2426434A - Waveform surface cleaning device

Info

Publication number: GB2426434A
Application number: GB0510508A
Authority: GB
Inventors: Christopher Davies
Original assignee: Carglass Luxembourg SARL Zug Branch
Current assignee: Carglass Luxembourg SARL Zug Branch
Priority date: 2005-05-24
Filing date: 2005-05-24
Publication date: 2006-11-29
Also published as: GB0510508D0; GB2426434A8

Abstract

A waveform surface cleaning device and associated method, feature first and second vibrational transducers which can apply waves, normally in the ultrasound range, to clean a surface, such of ice or liquid, by the vibrational interaction of the waveforms generated. The cleaning device may control the parameters of the two interacting waves, to optimise the cleaning effect of the combined wave pattern. The frequency range may typically be 20-30 kHz, and may be provided by radial transducers. The device may find application in the cleaning of vehicle windscreens.

Description

Method and Apparatus for Amelioration of Condensation Ice, or Precipitation

Accumulation at a Surface The present invention relates to amelioration of condensation ice, or precipitation accumulation at a surface, particularly in vehicular applications, such as for example the amelioration of ice, condensation or other precipitation accumulation or formation on a vehicle windscreen. It is known that the formation of ice and condensation on vehicle glass restricts visibility and unless suitable sprays are at hand, it can take some time to heat the windscreen from the inside of the vehicle to remove the build up of condensation or ice. There is therefore merit in devising a technique for an efficient means of de-icing and/or demisting of vehicle glass, and also to inhibit the formation of films of ice on vehicle glass such that any build up can be removed easily. Ice or precipitation accumulation on other surfaces can also cause problems and technical difficulties. The present invention provides a method of conditioning a surface to ameliorate condensation, ice, or precipitation build up on the surface, the method comprising applying to act at the surface first and second mechanical waves, wherein the first and second mechanical waves interact to result in a superposed waveform. In a first realisation of the invention the frequencies of the first and second waves are different, the difference in the frequencies of the waves resulting in a beat wave propagating over the surface. It is preferred that the frequencies of the first and second waves are in the ultrasonic range. Preferably the beat frequency is in the ultrasonic range. Desirably, the beat frequency is substantially in the range 20kHz-30kHz.

Prior art proposals using ultrasound have not succeeded technically or commercially. Utrasound techniques have been found to be technically feasible for small areas (such as vehicle wing mirrors) however such techniques are not workable for large areas (such as vehicle windscreens), as a result of the high degree of attenuation of the ultrasonic vibration. Ultrasonic frequencies are preferred due to their being inaudible, however the attenuation is proportional to frequency. To be inaudible, the mechanical waves need to operate above the threshold frequency of about 20kHz, and for the dimensions of associated transducer to be unobtrusive, the frequency is required to be of the order of 100kHz. In a second realisation of the invention, the first and second mechanical waves are out of phase, either temporally or more preferably spatially. This results in a more complex superposition relationship and more complex 'beat' waveform. Beneficially the first and second waves are of the same frequency. Again it is preferred that the frequencies of the first and second waves are in the ultrasonic range. In a third realisation the first and second waves are frequency and/or amplitude modulated out of phase to sweep through the bandwidth resulting in a complex superposed waveform. In this realisation the first and second waves may be of the same frequency. Again, the frequencies of the first and second waves are preferably in the ultrasonic range. In any of the realisations of the invention, it is preferred that the first and second waves are applied to the surface at a common application zone, which application zone comprises a minor proportion of the overall area of the surface. The waves however travel over a major portion of the surface and certainly a significant portion of the surface beyond the application zone. It is preferred that the application zone comprises substantially 20% or less by area of the overall area of the surface. More preferably the application zone comprises substantially 10% or less by area of the overall area of the surface. It is preferred that first and second vibrational transducers are used to set up the first and second mechanical waves acting on the surface. Beneficially the first and second transducers are ultrasonic transducers. One or other (or both) of the transducers may be a radial transducer, directing waves along the surface. It is less preferred that one or other (or both) of the transducers may be a longitudinally vibrating transducer directing waves transverse to the surface. According to a further aspect, the present invention provides apparatus for conditioning a surface to ameliorate the accumulation of condensation, ice, or precipitation on the surface, the apparatus comprising first and second vibrational transducers arranged to supply mechanical waves to the surface. Preferred features and aspects of the apparatus correspond to features identified in relation to the method of the invention, and are set out in the appended claims and this description. The invention is particularly applicable to vehicle surfaces, such as vehicle windscreens which require de-misting or de-icing. Another example of a vehicular surface is an aeroplane aeleron which may be required to be maintained ice free. The invention has application in situations in which vehicle surfaces need to be maintained precipitation, ice or condensation free prior to use (for example when the vehicle has laid dormant for a period). The waves may be applied intermittently or constantly in the dormant phase to prevent accumulation; alternatively, the waves may be activated at the end of the dormant phase to ready the surface prior to the vehicle becoming operational. For example the waves may be applied constantly or intermittently to a vehicle windscreen to maintain the windscreen ice-free whilst the vehicle is parked overnight in cold conditions. The windscreen is therefore ice/condensation free for operation of the vehicle next morning. The arrangement of the invention can also aid in removal of rain or other precipitation from a windscreen by conventional wipers. It is known that surface mechanical waves travelling over glass lower the adhesion of water on its surface by lowering the contact angle with the glass. This means instead of forming a uniform film, the water forms discrete beads which tend to move off the glass particularly under the action of air flow during vehicle motion. The beading of the water is found to provide: 1. Increased visibility as more free glass surface is exposed; 2. Easier removal of water from the screen, meaning less action required from wipers; 3. More efficient removal of water during driving - wind action tends to clear the screen; and, 4. Immediate drive away in frost conditions as droplets freeze but leave significant areas free of glass. The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which; Figure 1 is a schematic view of a surface (vehicle windscreen) fitted with vibrational transducers for performance of the invention; Figure 2 is a schematic representation of a radial transducer used in accordance with the invention; Figure 3 is a schematic representation of a longitudinal transducer used in accordance with the invention; and; Figure 4 is a schematic graphical representation showing the bandwidth for a frequency and amplitude modulation technique in accordance with the invention. In the following description, by way of example, the invention is explained in terms of application to the external surface 12 of a vehicle windscreen 11. A pair of radially vibrational ultrasonic transducersl,2 are arranged to produce output vibrational frequencies Fl, F2 respectively. An exemplary radially vibrational transducer 1 is shown in figure 2. The transducer vibrates radially in the direction of arrow A and the vibration is applied to the external surface 12 of the windscreen 11 via a coupling adhesive layer 14. As mentioned above prior art techniques have failed due to the nature of the high attenuation of mechanical vibration at ultrasonic frequency. The present invention overcomes this attenuation issue by using two transducers that have resonant frequencies that are close but not the same. The two frequencies, F1 and F2, are such that they combine to form a substantially lower beat frequency F3. This lower frequency F3 is attenuated less than the two driver frequencies F1 and F2 and so travel easier across the surface 2 of the windscreen 1. the driver frequencies Fl and F2 can be chosen to either give a beat frequency F3 in the audible range (e.g. F1 - 100 kHz, F2 = 95 kHz then F3 = Fl - F2 = 5 kHz) or in the ultrasound range (e.g. Fl = 120 kHz, F2 = 100 kHz and F3 = 20 kHz).In certain applications, for example where the system of the invention is to be used in the presence or proximity of persons (e.g vehicle occupants) inaudible beat frequency is preferred. Beat frequency in the ultrasonic range is therefore preferred in such situations. In other situations beat frequency in the audible range may be acceptable or even preferred. In general terms, the closer Fl and F2 are to each other then the lower is the attenuation of the beat frequency and so the wider is the energy coverage over the surface 2. The transducers 1, 2 are placed in close proximity to one another, the superposed waves extend to travel across a large proportion of the screen. Other pairs of couple transducers may be positioned at other locations of the surface 2 in order to maximise effective coverage. Radial or longitudinal emitting transducers can be used to generate the driving frequencies. With radial emitting transducers a sinusiodally varying drive voltage will generate a mechanical strain in the radial direction as shown by arrow A in figure 2. This strain will in turn set up mechanical waves in the glass that will radially propagate along the glass surface region (there will be some transmission of energy into the sub surface bulk of the glass). Alternatively longitudinal resonating transducers can be used which will transmit the bulk of their energy into the thickness of the screen. the divergence of the energy from each transducer together with the reflections from the different layers of the screen will create a complex interference pattern generating many other potential transient frequency components other than the beat frequency F3. The radially resonating system is deemed to be the optimal design due to its efficiency in propagating energy along the surface. It is possible to optimise the direction of energy propagation in the screen by angling the transducer relative to the surface. As shown in figure 3 a longitudinally vibrating ultrasonic transducer 22 (vibrating in axial direction B) can be mounted on a wedge 9, where a component of the mechanical vibration is in the direction of the plane of the windscreen surface 2, or by mounting the transducer on the edge of the screen (this arrangement is not shown). In the latter case the energy is directed straight into the side and along the plane of the screen. These represent other methods of introducing ultrasound energy into the screen, but these are expected to be not as efficient as direct coupling using radially vibrating transducers. Another method of driving the system is to use two transducers with the same frequencies (i.e. Fl = F2). Here the transducers can be placed more remote from each other (not at nodes on the screen surface 2) so that the waves are out of phase and a complex wave pattern is generated. Alternatively the transducers can be placed along side each other and driven out of phase. The preferred method of driving the transducers will be to drive each not only out ofphase but to sweep through the resonant frequency between the 3dB points. A piezoelectric transducer will typically have a wide Q which gives a narrow centre (resonant) frequency and bandwidth. the width (in Hz) between the 3dB (halfpower) points on each side ofthe resonant frequency gives the bandwidth (see figure 4).By sweeping through the bandwidth on both transducers not only are you frequency modulating (by changing F3) but also amplitude modulating due to the frequency response of each transducer. The present invention provides a convenient technique for ameliorating the accumulation of precipitation, ice or condensation (or other liquid media) on a surface, using vibrational energy.

Claims

Claims:

1. a method of conditioning a surface to ameliorate condensation, ice, or precipitation build up on the surface, the method comprising applying to act at the surface first and second mechanical waves, wherein the first and second mechanical waves interact to result in a superposed waveform.

2. a method according to claim 1, wherein the frequencies of the first and second waves are different, the difference in the frequencies of the waves resulting in a beat wave propagating over the surface.

3. a method according to claim 2, wherein the frequencies of the first and second waves are in the ultrasonic range.

4. a method according to claim 3, wherein the beat frequency is in the ultrasonic range.

5. a method according to claim 4, wherein the beat frequency is substantially in the range 20kHz-30kHz.

6. a method according to claim 1, wherein the first and second mechanical waves are out of phase.

7. a method according to claim 6, wherein the first and second waves are of matched frequency.

8. a method according to claim 7, wherein the first and second waves are spatially out of phase.

9. a method according to any of claims 6 to 8, wherein the frequencies of the first and second waves are in the ultrasonic range.

10. a method according to claim 1, wherein the first and second waves are of matched frequency, the waves being frequency and/or amplitude modulated to sweep through the bandwidth resulting in a complex superposed waveform.

11. a method according to claim 10, wherein the frequencies of the first and second waves are in the ultrasonic range.

12. a method according to any preceding claim, wherein the first and second waves are applied to the surface at a common application zone, which application zone comprises a minor proportion of the overall area of the surface.

13. a method according to claim 12, wherein the application zone comprises substantially 20% or less by area of the overall area of the surface.

14. a method according to claim 13, wherein the application zone comprises substantially 10% or less by area of the overall area of the surface.

15. a method according to any preceding claim, wherein first and second vibrational transducers are used to set up the first and second mechanical waves acting on the surface.

16. a method according to claim 15, wherein the first and second transducers are ultrasonic transducers.

17. a method according to claim 15 or claim 16, wherein one or both of the transducers is a radial transducer, directing waves along the surface..

18. a method according to any of claims 15 to 17, wherein one or both of the transducers is a longitudinally vibrating transducer directing waves transverse to the surface.

19. apparatus for conditioning a surface to ameliorate the accumulation of condensation, ice, or precipitation on the surface, the apparatus comprising first and second vibrational transducers arranged to supply mechanical waves to the surface.

20. apparatus according to claim 19, wherein the transducers are tuned to produce waves of different frequencies, the difference in the frequencies of the waves resulting in a beat wave propagating over the surface.

21. apparatus according to claim 19 or 20, wherein the first and second transducers are tuned to produce frequencies in the ultrasonic range.

22. apparatus according to claim 19, wherein the transducers are arranged to produce out of phase mechanical waves.

23. apparatus according to claim 22, wherein the transducers are arranged to produce waves are of matched frequency.

24. apparatus according to claim 19, wherein the transducers are arranged to produce first and second waves are of matched frequency, the transducers being driven such that the waves are frequency and/or amplitude modulated to sweep through the bandwidth resulting in a complex superposed waveform.

25. ' apparatus according to claim 24, wherein the transducers are arranged to produce waves having frequencies in the ultrasonic range.

26. apparatus according to any of claims 19 to 25, wherein the first and second transducers are configured to apply the waves to the surface at a common application zone, which application zone comprises a minor proportion of the overall area of the surface.

27. apparatus according to claim 26, wherein the application zone comprises substantially 20% or less by area of the overall area of the surface.

28. apparatus according to claim 27,wherein the application zone comprises substantially 10% or less by area of the overall area of the surface.

29. apparatus according to any of claims 19 to 28, wherein the first and second transducers are ultrasonic transducers.

30. apparatus according to any of claims 19 to 29, wherein one or both of the transducers is a radial transducer, directing waves along the surface.

31. apparatus according to any of claims 19 to 30, wherein one or both of the transducers is a longitudinally vibrating transducer directing waves transverse to the surface.

32. a method or apparatus according to any preceding claim, in which the surface to which the waves are applied is a vehicle surface.

33. a method or apparatus according to any preceding claim, in which the surface to which the waves are applied is a vehicle glazing panel.

34. a method or apparatus according to any preceding claim, in which the surface to which the waves are applied is a vehicle surface, the waves being capable of being applied in circumstances in which the vehicle is in dormant mode.