Patent Application
20200322524
The present invention relates to drones adapted for viewing a distant scene, and more particularly light drones, typically less than 25 kg. The present description also relates to methods for forming images using such drones.
Drones, or UAVs (Unmanned Aerial Vehicles), are uninhabited aircraft, piloted remotely and capable of performing specific tasks during their flight.
Drones, originally developed for military applications, are now also being developed for civilian purposes, for example for commercial applications or road or agricultural surveillance applications. Known for example are the Bebop® drone by the company Parrot® or the S1000® and Phantom 4® drones by the company DJI®. These drones are so-called light drones, with a mass typically below 25 kg.
Drones are generally equipped with a motor, or several rotors driven by respective motors, a series of sensors (accelerometers, rate gyros, altimeters, etc.) and a front camera intended to capture images of the scene toward which the drone is moving. A vertical-facing camera may also be provided to guarantee stabilization of the drone and/or to capture images of the overflown terrain. The front camera is generally a so-called “short focal distance” camera. A short focal distance camera is a camera provided with an optical system whereof the focal distance is generally less than 35 mm equivalent 24×36, corresponding approximately to a diagonal field of 63°. Short focal distance cameras allow the acquisition of images with a large field angle, i.e., for which the field of the image is wider than the field of view of a person.
There is currently a need for a drone equipped with a camera having a limited field angle allowing an acquisition of detailed images of the scene, i.e., enlarged images relative to human vision, or at least corresponding substantially to human vision.
Traditional cameras with a standard or restricted field angle are commercially available. However, these cameras may be difficult to adapt for light drones. Indeed, obtaining an enlarged image requires using a camera with a long focal length, i.e., a focal length greater than 50 mm, equivalent 24×36, which corresponds approximately to a diagonal field of 47°. The depth of field is generally defined as the region of space in which an element of the scene must be found to be able to obtain an image that the optical system accepts as sharp. It is inversely proportional to the square of the focal distance; thus, the depth of field of an image with a restricted field angle is short, which requires a very precise focusing of the optical system. In traditional cameras, the focusing, or adjustment of the focus, is done using high precision mechanical systems. Yet these mechanical systems are sensitive to vibrations, and are also too heavy and too cumbersome for drones, which, by their design, are heavy and subject to vibrations.
One aim of the present description consists of proposing a drone adapted for viewing a distant scene, the on-board camera of which is compatible with the constraints of a light drone, namely a camera in particular having a low mass and a low sensitivity to vibrations, and which also guarantees an acquisition of detailed images with precise focusing.
According to a first aspect, the present invention relates to a drone adapted for viewing a distant scene, comprising a flying platform and at least one first camera mechanically secured to the platform, wherein the first camera comprises:
Such a drone has the advantage of providing enlarged images of a scene relative to the vision of a human being, or substantially corresponding to the vision of a human being, with very good focus, which allows the user to assess the details of the scene that would not be visible in a wide-angle image.
According to one or several example embodiments, the diagonal angular field of the camera smaller than 32°, corresponding to a focal distance greater than 75 mm equivalent 24×36. According to one or several example embodiments, the diagonal angular field of the camera smaller than 16°, corresponding to a focal distance greater than 150 mm equivalent 24×36.
The electro-optical device adapted to the adjustment of the focus according to the present description may comprise any device having a focal distance variable by electrical command Such a device has the advantage, relative to a device implementing a movement of an optical element for the adjustment of the focus, of not being sensitive to vibrations.
According to one or several example embodiments, the electro-optical device with variable optical power comprises an optical diopter deformable by electrical command; this may for example be a device having an electrically deformable liquid liquid interface (for example a liquid lens with electro-wetting of the Varioptic® type) or it may be a device having a deformable polymer membrane (see for example the Polight®, Wavelens®, Optotune® technologies).
According to one or several example embodiments, the electro-optical device with variable optical power comprises a liquid crystal device (for example, the Lensvector® technology).
According to one or several example embodiments, the electro-optical device with variable optical power is positioned on the front face of the electro-optical system, the detection surface being positioned on the rear face of said electro-optical system.
According to one or several example embodiments, the electro-optical system includes at least two optical groups, which are fixed, each comprising a plurality of optical diopters, the electro-optical device with variable optical power being positioned between two of said optical groups.
According to one or several example embodiments, the electro-optical system comprises at least one positive optical group (optional), on the side of the object, followed by a second negative optical group, then symmetrically, a third negative optical group and a fourth positive optical group (optional), the electro-optical device with variable optical power being positioned between said two negative optical groups.
The first, second and third optical groups are for example respectively optical groups with a positive, negative, negative meniscus.
Positive or negative optical group refers to a respectively convergent or divergent optical group.
According to one or several example embodiments, the drone further comprises a telemetry device capable of measuring the distance between the scene and the electro-optical system, connected to the control unit of the electro-optical device with variable optical power, so as to allow an automatic focusing of the image as a function of the measured distance.
According to one or several example embodiments, the drone comprises a module for analyzing the sharpness of the image, the module for analyzing the sharpness of the image being connected to the control unit of the electro-optical device with variable optical power, so as to allow automatic focusing of the image based on the sharpness analysis.
According to one or several example embodiments, the first camera is mounted pivoting around at least one rotation axis connected to the flying platform. For example, the first camera rotates around all three rotation axes.
According to one or several example embodiments, the drone further comprises a second camera with a focal distance different from that of the first camera, adapted for observing the scene with a field different from that of the first camera.
The present description also relates to methods for forming images using drones according to the first aspect.
According to one or several example embodiments, the image method further comprises automatically focusing the image by varying the optical power using the electro-optical device with variable optical power.
According to one or several example embodiments, the automatic focusing of the image comprises:
According to one or several example embodiments, the automatic focusing of the image comprises:
Other advantages and features of the invention will appear upon reading the description, illustrated by the following figures:
In the figures, identical elements are identified using the same references. For legibility of the figures, the illustrated elements are not shown to scale.
An example drone, shown schematically by a rhomb referenced 10, is shown in
In
In these examples, the camera 40 comprises an electronic system (42, 43) and an image sensor 41, or image detector, with a detection surface 410 having given dimensions. The image sensor 41 can be a 1D or 2D sensor, for example of the CCD or CMOS type.
The electro-optical system comprises at least a first optical group 43, comprising a plurality of optical diopters and electro-optical device with variable optical power, referenced 42, and simply referred to hereinafter as “electro-optical device”. For a detection surface with given dimensions, the electro-optical system made up of the optical group(s) and the electro-optical device defines the diagonal angular field of the camera. In the present description, we consider a diagonal angular field smaller than or equal to 47°, which corresponds to a focal distance greater than 50 mm equivalent 24×36.
In the examples illustrated in
Each fixed group is made up of a set of several optical diopters; it may for example be made up of a fixed lens, convergent or divergent, or a set of several fixed lenses, convergent or divergent, assembled to one another to generate a specific optical function. Examples of optical groups will be described later in connection with
The electro-optical device 42 is an optical device whose optical power, which is inversely proportional to the focal distance, can be modified by varying the electrical voltage applied across the terminals of the electro-optical device. Such a device has the advantage of being able to perform focusing without mechanical movement of any of the optical elements making up said electro-optical device. A control unit 420 makes it possible to control the voltage applied to the electro-optical device.
According to one or several example embodiments, the electro-optical device with variable optical power comprises an optical diopter deformable by electrical command.
For example, the electro-optical device with variable optical power comprises a liquid lens with electro-wetting, for example a liquid lens as marketed by the company Varioptic®. Such a liquid lens is based on the deformation of a diopter formed by the interface between two liquids, including an electrically conductive liquid and an electrically nonconductive liquid, via the application of an electrical voltage. Such a liquid lens, described for example in patent FR 2,791,439 B 1, in particular has a high value of the optical power x useful opening diameter product, which makes it possible to produce a significant adjustment range of the optical power on a device having a pupil with a large opening diameter.
The electro-optical device with variable optical power may also comprise a deformable polymer membrane: this may for example use technologies marketed by the companies Polight® and Wavelens®, in which a transparent polymer membrane is controlled by an optical electromechanical microsystem (more simply called MEMs), or the technology marketed by the company Optotune®, in which a deformable polymer membrane separates two chambers filled with fluid with different refraction indices, the pressure in the two chambers being controlled to deform the polymer membrane.
According to one or several example embodiments, the electro-optical device with variable optical power comprises a liquid crystal device (for example the technology marketed by the company Lensvector®).
As illustrated in
According to one or several example embodiments, an image processing module, integrated into the ISP or into a control unit inside or outside the drone, makes it possible to determine the control voltage, to be applied to the electro-optical device 42 based on the image processing thus done, for example an analysis of the sharpness of the images, as will be described in more detail hereinafter.
According to one or several example embodiments, a phase detection system, integrated into the image sensor, can be used to determine the focusing to be done and the control voltage to be applied to the electro-optical device 42.
In the example shown in
The optical axis of the electro-optical system is denoted (A). The solid lines and the dotted lines show the paths of an incident light beam in the electro-optical system respectively following a first and a second direction.
In the example of
In these figures, Ømin denotes the diameter of the opening diaphragm 46 of the electro-optical system. In
One advantage of an electro-optical system of the type shown in
An electro-optical system of the type shown in
However, in an electro-optical system of the type shown in
Furthermore, in an arrangement of the “add-in” type as shown in
In the examples of
In the case of
In the examples shown in
A Cooke triplet generally comprises a combination of three optical groups, a first convergent optical group 43a, a second divergent optical group 43b and a third convergent optical group 43c, the divergent optical group being placed between the convergent optical groups, generally near the opening diaphragm. A Cooke triplet is an optical combination that allows a good correction of aberrations over a wide field.
As shown respectively in
In the example of
The system may comprise, from the object toward the image sensor, a first optical group 43a (optional), a second fixed optical group 43b, for example comprising two lenses and three or four optical diopters, the electro-optical device 42, a third fixed optical group 43c for example comprising two lenses and three or four optical diopters, a fourth optical group 43d (optional).
According to one or several example embodiments, the faces of the second and third groups 43b, 43c facing toward the electro-optical device 42 are concave and the faces of the second and third groups 43b, 43c facing away from the electro-optical device 42 are convex.
According to one or several example embodiments, the lenses of the second group and the third group formed cemented doublets.
According to one or several example embodiments, a glass slide or a spectral filter can be arranged between the electro-optical device and one or the other of the second and third optical groups.
One advantage of such an arrangement is the ability to produce an electro-optical system with an optical opening pupil diameter larger than the useful optical diameter of the electro-optical device with variable power.
Whatever the configuration of the electro-optical system, the camera 40 is mechanically secured to the platform 20 of the drone, i.e., mechanically connected to the platform and may be arranged on one face or the other of the platform (above or below). As shown in
The electro-optical system of the camera may be positioned along an axis substantially parallel to the axis X, substantially comprised in the plane of the platform, and thus provide a horizontal facing. According to one alternative, the electro-optical system of the camera 40 may be positioned along an axis substantially parallel to the axis Y substantially perpendicular to that of the platform, and thus provide a vertical facing.
In one or several embodiments, the camera 40 can be mounted rotating relative to the platform 20 of the drone. It can rotate along a single axis, for example the axis Z, as shown in
A step 820 consists of comparing the sharpness score N with the sharpness score of the previous image N−1 or two or more previous images. A step 830 next consists of modifying the value of the control voltage of the electro-optical device 42 based on the result of the comparison 820. The modification of the control voltage can be determined using a dichotomic algorithm A sharpness analysis of the following image N+1 is next done (step 840), which determines a sharpness score N+1. A test 850 consists of verifying whether the sharpness score has reached a predefined maximum score. If the maximum score is not reached, the method is repeated from step 810. If the maximum score is reached, then the focusing sequence is completed (step 860).
The automatic focusing methods previously described can be combined. It is thus possible to perform a first focusing based on a measurement of the distance, then to refine it through focusing done using image processing, for example a sharpness analysis.
According to one or several example embodiments, the drone according to the present invention includes a second camera 40B, for example a front camera, secured (or not) to a first camera 40A, for example a front camera, as shown schematically in
The first and second cameras 40A and 40B can each have their own processing unit (ISP) or share the same processing unit, as illustrated in
Although it has been described through a certain number of detailed example embodiments, the drone according to the present description comprises different alternatives, modifications and improvements that will appear obviously to one skilled in the art, with the understanding that these various alternatives, modifications and improvements are within the scope of the invention, as defined by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1654873 | May 2016 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/063026 | 5/30/2017 | WO | 00 |
