DEVICE FOR CLEANING AN OPTICAL SURFACE

Abstract

Disclosed is a device (5) for cleaning an optical surface, which device comprises: a transparent optical surface (10); a cleaning unit (15) for cleaning the optical surface, having a piezoelectric layer (20) and at least two wave transducers (45), each wave transducer having electrodes (40) of opposite polarity in contact with the piezoelectric layer and being acoustically coupled to the optical surface so as to generate at least one surface ultrasonic wave (W.sub.s) or a Lamb wave (W.sub.L) propagating in the optical surface, the transducers being further arranged on the periphery of the optical surface.

Claims

1. A device comprising: a transparent optical surface, an optical-surface cleaning unit comprising a piezoelectric layer and at least two wave transducers, each wave transducer comprising electrodes of opposite polarities in contact with the piezoelectric layer, and being acoustically coupled with the optical surface in order to generate at least one ultrasonic surface wave or a Lamb wave propagating in the optical surface, the transducers further being arranged at the periphery of the optical surface.

2. The device as claimed in claim 1, wherein the wave transducer extends from an edge of the optical surface over a distance less than 10%, or even less than 5% of the length of the optical surface.

3. The device as claimed in claim 1, the transducer extending from an edge of the optical surface over a distance less than 30 mm, preferably less than 20 mm, preferably less than 10 mm.

4. The device as claimed in claim 1, the piezoelectric layer forming at least one strip extending over one face of the optical surface.

5. The device as claimed in claim 1, the optical surface comprising a region of optical interest that is not superposed with the transducers and the piezoelectric layer forming a surround at least partially framing the region of optical interest.

6. The device as claimed in claim 1, the wave transducers being in contact with, for example bonded to, the optical surface.

7. The device as claimed in claim 1, the optical surface comprising an acoustically conducting portion, preferably made of glass, the wave transducers being acoustically coupled to the acoustically conducting portion.

8. The device as claimed in the claim 7, the piezoelectric layer being placed in contact with the acoustically conducting portion.

9. The device as claimed in claim 7, the optical surface comprising a stack comprising an acoustically insulating portion and the acoustically conducting portion (80) which are stacked one upon the other.

10. The device as claimed in claim 9, the acoustically conducting portion being mounted removably on the acoustically insulating portion.

11. The device as claimed in claim 1, the electrodes of each transducer being obtained by sputtering or printed, for example ink-jet printed.

12. The device as claimed in claim 11, the electrodes of each transducer being printed on a foil, for example made from a flexible thermoplastic material, and being applied by transferring the foil onto the piezoelectric layer.

13. The device as claimed in claim 1, the thickness of the piezoelectric layer being less than or equal to 5*, preferably less than or equal to 1.5*, preferably less than or equal to , or even less than or equal to 0.5*, notably for an ultrasonic surface wave with a frequency comprised between 0.1 MHz and 60 MHz.

14. The device as claimed in claim 1, the piezoelectric layer having a thickness comprised between 1 m and 300 m.

15. The device as claimed in claim 1, selected from: a motorcycle helmet comprising a shell intended to protect a motorcyclist's skull, and the optical surface being a visor mounted on the shell so as to protect all or part of the motorcyclist's face, a glazed element of a building, and the optical surface being glazing, and a motor vehicle, and the optical surface being a windshield of the vehicle, an automated motor vehicle, and the optical surface covering an optical sensor and/or an optical emitter, for example a lidar, photographic equipment, a camera, a radar, an infrared sensor or an ultrasound telemeter, and a component of a motor vehicle, notably automated, for example selected from a headlamp module, a system containing a collection of various sensors also referred to as a pod, at least one side window, a front screen or rear screen and a driving assist unit.

Description

[0077] The invention may be better understood from reading the following detailed description of nonlimiting exemplary embodiments thereof, and from studying the appended drawings, in which:

[0078] FIGS. 1 and 2 schematically depict, viewed face-on, examples of a device according to the invention,

[0079] FIGS. 3 to 5 schematically depict, viewed in cross section, examples of a device according to the invention, and

[0080] FIGS. 6 to 9 schematically depict further examples of a device according to the invention.

[0081] For the sake of clarity, the elements that make up the drawings have not always been drawn to scale.

[0082] FIG. 1 illustrates a first example of a device 5 according to the invention, viewed face-on.

[0083] The device comprises an optical surface 10 and a transparent optical surface cleaning unit 15.

[0084] The optical surface takes the form of a plate which may vary in shape, for example being rectangular as illustrated.

[0085] The optical surface cleaning unit 15 comprises a piezoelectric layer 20 which extends in a parallel strip between two opposite edges 25, 26 of the optical surface. The piezoelectric layer further extends on the periphery of the optical surface, along a third edge 27 that connects the opposite edges 25, 26.

[0086] The device comprises three pairs of electrodes 40 which have opposite polarities and are interdigital and in contact with the piezoelectric layer, thus forming three wave transducers 45. Naturally, this number of transducers is nonlimiting, provided that it is greater than or equal to two. It may be adapted to suit the size of the device in order to provide optimal cleaning of the optical surface.

[0087] The transducers are acoustically coupled to the optical surface, so that the waves that they generate can propagate in the optical surface. The cleaning unit may further comprise a current generator 50 for electrically powering the transducers by means of an electric circuit that has not been depicted in the figure.

[0088] The transducers may each generate an ultrasonic surface wave W.sub.S or a Lamb wave W.sub.L, which propagates in the optical surface in order to move a body 55, for example a raindrop, which may be in contact with the face of the optical surface on which the piezoelectric layer is positioned.

[0089] The device may be configured so that the transducers emit an ultrasonic wave toward the edge 28 opposite to the edge 27 along which the piezoelectric layer 20 extends as a strip. The body may thus be moved in the direction S of propagation of the wave and removed from the optical surface via the edge 28.

[0090] The device illustrated in FIG. 1 is easy to manufacture. The piezoelectric layer is for example applied using a cathodic sputtering technique and then the electrodes are printed onto the optical surface, for example in a single pass. It is thus possible to quickly position an appreciable number of electrodes on the piezoelectric layer to form transducers, unlike in the devices of the prior art known to the inventors, which require bonding of the transducers in position one by one. As an alternative, the electrodes may be preprinted onto a foil which is then applied to the piezoelectric layer so as to transfer the electrodes onto the piezoelectric layer, for example in the manner of a transfer.

[0091] The device depicted in FIG. 2 differs from the one illustrated in FIG. 1 in that the piezoelectric layer delimits a surround 60 which frames a region of optical interest 65. The surround is for example rectangular. The piezoelectric layer may be opaque, allowing an observer looking through the region of optical interest 65 to easily determine the extent of said region. The surround has an exterior contour 70 which coincides with the contour 75 of that face of the optical surface on which the piezoelectric layer is applied. Furthermore, the transducers may be arranged uniformly around the surround. It is thus possible to operate just some of the transducers in order to move a body according to the magnitude of an external force applied to the body, as described for example in application FR 1910589, incorporated by reference.

[0092] FIGS. 3 to 5 are schematic views in cross section of portions of examples of a device as depicted in FIGS. 1 and 2.

[0093] In the example illustrated in FIG. 3, the optical surface is monolithic and made from an acoustically conducting material, for example glass, and the piezoelectric layer is in contact with the optical surface and positioned at the periphery of the optical surface, against an edge 27. The piezoelectric layer 20 is further positioned between the electrodes 40 of the various transducers and the optical surface 10. When electrically powered, the transducers generate an ultrasonic surface wave W.sub.S or a Lamb wave which propagates in the optical surface until it reaches a body in contact therewith. The person skilled in the art easily knows how to determine the frequencies and amplitude of the wave in order to cause the body to move over the optical surface.

[0094] The example illustrated in FIG. 4 differs from the example illustrated in FIG. 3 in that the optical surface 10 comprises an acoustically insulating portion 75 completely covering an acoustically conducting portion 80, for example made of glass. The acoustically conducting layer may be mounted removably, for example using a reversible adhesive, on the acoustically insulating layer. Furthermore, although this is optional, the optical surface has a coating 90 completely covering one face 95 of the acoustically conducting portion and made up of a stack of an antireflection layer 100 and a hydrophobic layer 105 so as, for example, to prevent raindrops 40 from spreading over the optical surface 10 and to make them easier to remove. The piezoelectric layer is positioned in contact with the coating opposite the acoustically conducting portion. The coating preferably has a thickness that is small enough with respect to the wavelength of the surface wave generated by the transducer. Thus, the acoustically conducting portion and the transducer are acoustically coupled.

[0095] The device illustrated in FIG. 5 differs from the device illustrated in FIG. 6 in that the transducers 45 are sandwiched between the hydrophobic layer 100 and the acoustically conducting portion 80. Thus, the hydrophobic layer protects the transducers.

[0096] FIG. 6 schematically depicts a motorcycle helmet 120. The helmet comprises a shell 125, to protect a motorcyclist's head, and has an opening 130 and an optical surface 135 in the form of a transparent and curved visor to protect the motorcyclist's head from precipitation, projectiles and insects.

[0097] The visor is mounted on the shell with the ability to rotate and may be moved between a closed position in which the visor closes off the opening and an open position that allows air to pass through the opening toward the motorcyclist's head.

[0098] The visor may be made from an acoustically conducting material or may, as illustrated in FIG. 4, have an acoustically insulating portion and an acoustically conducting portion.

[0099] A piezoelectric layer 20 is arranged at the periphery of the visor 135. In FIG. 6, it is positioned along the upper edge 140 of the visor. However, other arrangements are conceivable. For example, it may be positioned against the lower edge 141 and/or against the lateral edges 142, 143 to form a surround as illustrated in FIG. 2.

[0100] As a preference, the transducers are arranged between the visor 135 and the shell 125 so as to be protected from precipitation. At least in the closed configuration, the piezoelectric layer may be completely superposed on the shell 125, for example on the outside 150 of the shell. In this way, the transducers are hidden from the motorcyclist's sight.

[0101] Another alternative is illustrated in FIG. 7. The device 5 depicted there is a motor vehicle 160 having a windshield 165. Piezoelectric layers 20 in strips are positioned along the windshield and extend at the periphery along the lower 170 and upper 171 edges of the windshield and between lateral edges 172, 173 thereof. The piezoelectric layer may be arranged on the face of the windshield opposite to the vehicle-interior compartment. Groups of electrodes 40 of opposite polarities are applied to each piezoelectric layer. Thus, the transducers can each generate an ultrasonic surface wave or a Lamb wave in order to clean off the precipitation that is in contact with the windshield. Such a vehicle may advantageously not be fitted with a wiper.

[0102] Another alternative is illustrated in FIG. 8. The device 5 depicted there is a window of a building 180.

[0103] The window for example comprises a fixed frame 185 and one or more opening 190, for example two as illustrated, hinged to the fixed frame.

[0104] Each opening comprises a framing structure 195 into which glazing 200 is fitted. A piezoelectric layer 20 is arranged at the periphery of the glazing, preferably along the upper part of the glazing, and at least two groups of electrodes are positioned in such a way as to generate acoustic waves W oriented from top to bottom, so as to facilitate the movement of the drops under the effect of gravity G. In the example illustrated, the piezoelectric layer has a part not superposed with the framing structure. In an alternative that has not been depicted, the piezoelectric layer may be sandwiched, for example completely, between the framing structure 195 and the glazing 200 so as to be concealed from the sight of an observer looking through the glazing. Any other glazed element of a building may naturally be envisioned.

[0105] Finally, FIG. 9 depicts yet another alternative of a device 5 according to the invention, which is part of an automated vehicle.

[0106] The device comprises an optical surface 10, an optical surface cleaning unit 15 and an item of equipment 210.

[0107] The item of equipment comprises a sensor 215 to capture radiation R and a lens to direct the radiation R toward the sensor. As an alternative or in addition, it may comprise an emitter to emit radiation. For example, the item of equipment comprises a lidar which is configured to emit laser radiation and in return capture that part of this laser radiation that has been reflected by an object.

[0108] Further, the lens 220 is optional. In an example which is not depicted, the item of equipment does not have one.

[0109] The item of equipment defines an optical field C.sub.O which corresponds to the portion of space from which it is able to capture radiation. Outside of this optical field, even though the radiation may be able to reach the sensor, the latter is not able to capture it.

[0110] Furthermore, the optical surface completely covers the sensor.

[0111] In the example illustrated, the optical surface takes the form of a disk of which the thickness e.sub.p is for example comprised between 0.5 mm and 5 mm. In an alternative, the optical surface may be curved and for example have the shape of a lens.

[0112] The device may, as illustrated, comprise a housing 225 which defines a chamber 230 housing the sensor. The chamber may notably be delimited by a solid wall 235 of the housing and by the optical surface 10 so as to be airtight and watertight. The sensor is thus protected against poor weather.

[0113] In particular, the optical surface may close off the housing 225. For example, the optical surface is mounted on a ring 240 screwed onto the housing.

[0114] The optical surface is thus removable, allowing it to be replaced with ease when it becomes damaged.

[0115] The optical surface cleaning unit comprises transducers 45 which are arranged in contact with and acoustically coupled to the optical surface 10. The transducers share the same piezoelectric layer. The cleaning unit further comprises a current generator 50 for electrically powering the transducers.

[0116] In the example illustrated in FIG. 9, the transducers are arranged on the face 250 of the optical surface 10 opposite to the face 255 that is to be cleaned. They are preferably configured to generate a Lamb wave that reaches the face that is to be cleaned.

[0117] Moreover, the transducers delimit a region of optical interest 65 which is not superposed with the transducers.

[0118] As a preference, part of the region of optical interest 65 is contained within the optical field C.sub.O of the item of equipment. In other words, the transducers are positioned outside of the optical field of the item of equipment so that they create almost no interference with the radiation passing through the region of optical interest and captured by the sensor.

[0119] In order to reduce bulk, as illustrated in FIG. 9, the transducers are arranged at the periphery of the optical surface. In this way, the surface area of the region of optical interest can be maximized.

[0120] Of course, the invention is not limited to the exemplary embodiments of the invention that have been provided by way of non-limitative illustrative example.