This invention relates to a system controlling the wiping of automotive windscreens at a rate corresponding to the determined amount of water on the screen. BACKGROUND ART

In Australian patent 546327, a detector mounted externally of the vehicle continuously monitors rain to provide a value for the amount of rain fallen since the completion of the last wipe of the windscreen wiper blade. Once that rain total reaches some predetermined level the wiper blade is again actuated. Such is typical of prior art automatic windscreen controls which integrate detected actual rain fall signals in order to determine the rate or frequency of windscreen wiper operation.

However, such systems are in general deficient at least in regard to the fact that the windscreen needs to be wiped, not only in consideration of rain fall, but also in consideration of other water sources such as spray from near by cars.

DISCLOSURE OF INVENTION

In the present invention moisture on the windscreen itself is detected by detecting the amount of light reflected by the surface of the windscreen. Accordingly, in one broad form, the present invention can be described as a method for determining moisture on a windscreen surface comprising directing light at the windscreen so as to be reflected by the windscreen surface and detecting the amount of reflected light so as to sense moisture on the surface.

The invention can alternatively be described as providing a device comprising a light source directing light on to a surface of a windscreen, and a light detector positioned to detect the directed light when reflected by the windscreen surface so as to sense moisture on the surface.

Preferably the light is in the infra-red range emitted by a light emitting diode, however an infra-red laser beam may also be used.

Preferably the light source and the detector are located in a rear face of a prismatic lens to be held with its opposite front face substantially flush against the windscreen. The prismatic lens preferably includes respective transmitting and receiving internal reflective surfaces disposed on opposite sides of the prism proximate respectively the source and the detector. BRIEF DESCRIPTION OF THE DRAWINGS In the attached drawings:

Fig. 1 (A-B) schematically show an exemplary embodiment of the invention detecting the moisture state on the out side of a windscreen;

Fig. 2 (A-B) is a schematic representation of an exemplary embodiment of the invention detecting the moisture state of the inside of a windscreen; and

Fig. 3 (A-C) are sectional views of a preferred design of the layout shown in Fig. 1 and a schematic representation of the light beam pattern that it produces. BEST MODE OF CARRYING OUT THE INVENTION

An infra-red light beam is provided by diode (LED) 4 and directed generally along the path 5 toward windscreen 7. The angle of incidence is selected such that at least a high proportion of the beam 5 travels through the material of windscreen 7 to be internally reflected off the outside surface 1, when the outside surface 1 is dry, to continue along the path 5 to detector 6.

The presence of water, such as water drops 3, on the outside surface 1 at the point of incidence of beam 5, will result in a substantial portion of defused light 8 being lost from the beam 5. Thus, with water on the outside of the screen 7, the amount of light detected at

detector 6 is diminished thus allowing detector 6 to provide a signal to a logic circuit or other electronic device, which is indicative of the presence of water on the windscreen 7. It will be clear that the operation of the device depends upon the presence of water altering the refractive index at the screen/air exterior interface. As such operation of the device is not restricted to detecting water droplets, but will also detect for example ice. Thus, throughout this specification, it should be clear that the term "wet" defines the presence of water in any state and the term "dry" defines the absence of water in any state.

A wiper control circuit device, not shown in Fig. 1, is connected to the detector and upon receipt of the signal indicating water on.the screen 7, can initiate a first wiping action of the windscreen wiper blades. The moving wiper blade produces a wall of water along its leading edge being characteristically proportional to the amount of water that was on the windscreen 7 at the time of the wiper blade sweep. As this wall of water passes the point of incidence of the laser beam 5, the detector 6 receives a varying amount of reflected light beam 5 and thus produces a signal which is directly related to the amount of moisture that was wiped by the blade from the screen. This signal indicating the amount of moisture on the screen is then processed and used to control the next sweep of the blade. Such control of the blade can be related to the blade speed or lag time between the last and next sweep of the blade.

When the screen 7 becomes dry the reflected beam 5 reaching the detector 6 become constant and the wipers are switched off.

In Fig. 2 the infra red beam 15 is directed at the windscreen 7 at an angle of incidence so as to create ^'

substantial external reflection from the inside surface 2 of the windscreen 7. Here, the presence of misting, creating moisture condensation 9, on the inside 2 is measured by detector 16, where the amount of light detected is diminished due to light dispersion 19, in a manner similar to that described before hand with reference to the Fig. 1 embodiment. In this case detector 16 is connected via circuitry to demisting equipment of the vehicle. Figs. 3A and B show in plan similar integral assemblies 10 and 20 which embody in a particular form the devices shown in Fig. 1 and described above.

The assembly 10 includes a front window 12 which is transparent to infra red light and which is adhered to, and optically matched with, the inside surface 2 of the windscreen 7. In a rear face of the window 12 is an array of three infra-red LEDs 4 to produce beams 5 angled at the screen 7. The light beams 5 strike the outside surface 1 at the desired angle of incidence to be reflected back into the window 12 impinge on a matching set of three diode light receivers 6.

Respective pairs of co-operative LED 4 and detector 6 are housed in their own module 13, three modules 13 being located side by side within a case enclosure 11, creating a pattern of three closely spaced illumination points which ensure correct operation with defective wiper blades. The device is well adaptable to rear windscreens of cars which include wipers.

The assembly 20 comprises six of the modules 13 arranged in two rows of three. The pattern of illumination by assembly 20 is shown in Fig. 3C and allows connected electronics (not shown) to override deleterious effects such as debris, e.g. impacted insects, as well as water streaks caused by faulty wiper blades. The assembly 20 is fixed with the front face of the window 12 flush

against the screen surface 2 at any convenient point aligned with a portion of the outside surface 1 wiped by a wiper blade 14. In a typical road vehicle front windscreen this can often be between the screen and the interior rear vision mirror. INDUSTRIAL APPLICABILITY

The windscreen may be any screen which is to be kept clear of rain or similar by some controllable cleaning mechanism such as, but not necessarily, a pendulous wiper. It does have particular use in road vehicles, boats and aeroplanes.