FR3080923A1 - DEVICE AND METHOD FOR DETECTING OBJECTS - Google Patents

Abstract

The invention relates to an object detection device (20) for a motor vehicle (10), comprising: - a transmitter adapted to emit a light beam, - a spherical lens with adjustable focal length, adapted to focus said light beam, and a receiver (28) adapted to receive a part of said light beam which has been reflected by said obstacle. According to the invention, there is further provided a biconical lens smaller than the spherical lens and located upstream thereof, in the path of the light beam.

Description

Object detection device and method

Technical field to which the invention relates

The present invention relates generally to the detection and monitoring of an object by an optical method.

It relates more particularly to an object detection device for a motor vehicle, comprising:

- a transmitter adapted to emit a light beam,

- an optical system which comprises a spherical lens with adjustable focal distance, which is adapted to focus the light beam leaving the transmitter,

- a receiver adapted to receive part of the light beam after it has been reflected by an object, and

means for controlling the focal distance of the spherical lens.

It also relates to a method for controlling the focal distance of a spherical lens of such an object detection device.

The invention is particularly applicable to the detection of obstacles located on the path of the motor vehicle or close to it.

Technological background

Different types of obstacle detection devices are known, based on the use of cameras or transceivers.

It is notably known to use laser diodes as transceivers. The emitting diodes are then designed to emit a beam of light in a preferred direction, in a restricted emission field around this preferred direction. So when an obstacle is within the range of the transmitter and within range, part of the light is reflected by this obstacle towards the receiver. A computer is then able to determine the distance between the vehicle and the obstacle, by measuring the time taken for the light to make a round trip.

An optical lens, for example a Fresnel lens, is generally used to focus the light beam emitted by the transmitter, so as to increase the range of the obstacle detection device.

The disadvantage of this device is that it necessarily reduces the transmitter's field of emission. More precisely, the light beam is then emitted in an emission cone whose apex angle is all the more narrower than the optical lens concentrates the light beam.

It is therefore understood that if this device makes it possible to detect obstacles located at long ranges in the axis of the vehicle, it does not make it possible to detect obstacles situated at an angle to the vehicle, which may prove to be insufficient, especially in town .

It is then known to use a liquid lens whose focal length is adjustable. Thanks to this liquid lens, it is possible to reduce the focal distance of the lens in order to favor the range of obstacle detection. It is also possible to increase this focal distance so as to increase the emission field of the transmitter, for example when the vehicle is moving in town or when it is traveling at reduced speed.

Object of the invention

The present invention provides an optical system which also uses an adjustable focal lens, but which also makes it possible to better focus the light beam in the direction of the obstacles that the vehicle may potentially encounter.

More particularly, according to the invention, an object detection device as defined in the introduction is proposed, in which said optical system also comprises a biconical lens which is located between the emitter and the spherical lens and which has a diameter strictly lower than that of the spherical lens.

Here, it is therefore proposed to use a biconical lens which makes it possible to continuously crush the light beam over a reduced height, in the direction of the road, so as to concentrate it in the direction of the objects situated on the road. The range of the light beam in this direction is thereby increased.

The spherical lens has a given diameter, generally quite small.

The biconical lens is then here located between the emitter and the spherical lens so as to be able to have a diameter smaller than that of the spherical lens. Adding this biconical lens to the optical system therefore does not cause any additional bulk.

Note also that such a biconical lens has a reduced cost, so that its use does not significantly increase the price of the entire device.

Other advantageous and non-limiting characteristics of the device according to the invention are as follows:

said biconical lens having an optical axis, as well as a first axis and a second axis perpendicular to each other and perpendicular to the optical axis, the biconical lens has non-zero optical power along the first axis and zero optical power along the second axis;

- Said biconical lens has a cylindrical optical power and a distance from the emitter such that the light beam has, at its exit from the biconical lens, an opening angle of between 5 and 15 degrees in a plane which includes an optical axis of the biconical lens and which is perpendicular to a first axis of orientation of the cylindrical optical power of the biconical lens;

- said biconical lens is made of plastic;

- said spherical lens has a diameter less than 12 mm;

- Said spherical lens comprises, on the one hand, a capsule which internally delimits a housing for a conductive liquid, and, on the other hand, at least one pair of electrodes;

- Said control means are adapted to control the electric voltage across said electrodes;

- Said transmitter comprises at least one diode.

The invention also provides a method for controlling the focal length of a spherical lens of an object detection device as mentioned above, in which it is provided:

- a step of determining a focal distance value,

- a step of piloting the focal distance of the spherical lens so that it has said value, then

- an impulse step during which said emitter emits a light beam and during which the focal distance of the spherical lens is controlled to remain invariable.

Preferably, in the determination step, said value is determined as a function of at least one of the following parameters:

- speed of the motor vehicle,

- orientation of the steering wheels of the motor vehicle,

- distance separating the motor vehicle from said obstacle,

- motor vehicle environment.

Detailed description of an exemplary embodiment

The description which follows with reference to the appended drawings, given by way of nonlimiting examples, will make it clear what the invention consists of and how it can be carried out.

In the accompanying drawings:

- Figure 1 is a schematic perspective view of a motor vehicle carrying an obstacle detection device according to the invention;

- Figure 2 is a schematic side view of the transmitter and the system of the obstacle detection device of Figure 1, shown when the spherical lens has a reduced focal distance;

- Figure 3 is a graph illustrating the variation of the light intensity of light rays leaving the spherical lens of Figure 2, as a function of the angular difference separating the light ray considered from the optical axis of the spherical lens in the horizontal plane;

- Figure 4 is a schematic side view of the transmitter and the optical system of the obstacle detection device of Figure 1, shown when the spherical lens has a large focal distance; and

- Figure 5 is a graph illustrating the variation of the light intensity of light rays leaving the spherical lens of Figure 4, as a function of the angular difference separating the light ray considered from the optical axis of the spherical lens in the horizontal plane.

In FIG. 1, a motor vehicle 10 is shown.

This motor vehicle 10 is here a car comprising four wheels 13, including two driving and steering front wheels. Alternatively, it could be a motor vehicle comprising two or three wheels, or more than four wheels.

Conventionally, this motor vehicle 10 comprises a chassis which in particular supports a powertrain 14 (namely an engine and means for transmitting the torque from the engine to the drive wheels), a steering system for varying the orientation of the two front steered wheels , a brake system for the wheels 13, bodywork elements and cabin elements.

The motor vehicle 10 also includes an electronic control unit (or ECU for Electronic Control Unit), here called a computer 21.

This computer 21 includes in particular means for controlling the steering system of the steered wheels, the braking system for the wheels 13, and the powertrain 14. These control means thus make it possible to vary the orientation of the steered wheels 13, to control braking the motor vehicle 10 and varying the speed and the load delivered by the powertrain 14, without the intervention of the driver.

In the context of the present invention, the motor vehicle 10 also comprises an object detection device 20. It is more specifically here an obstacle detection device suitable for detecting obstacles located at the front of the vehicle. The motor vehicle 10 also comprises at least one alert means 17, 18 adapted to emit an alert signal when an obstacle is detected by the obstacle detection device 20.

The obstacle detection device 20 comprises, in addition to the computer

21, means 25 for emitting a light beam and a receiver 28 adapted to receive part of this light beam after it has been reflected by an obstacle.

More precisely, as shown in FIGS. 2 and 4, the emission means 25 comprise a transmitter 26 adapted to emit the light beam

22, and an optical system 27 adapted to focus this light beam 22 at its output from the transmitter 26.

The optical system 27 is therefore located on the emission axis of the transmitter 26. More precisely here, the optical system 27 is placed in such a way that its optical axis A1 merges with the emission axis of the transmitter 26.

The obstacle detection device 20 thus forms a LIDAR sensor, and more precisely here a laser remote sensor.

The transmitter 26 of the obstacle detection device 20 here comprises a single laser diode. It could alternatively include an array of several laser diodes. According to another variant, it could be one or more light-emitting diodes (emitting in the visible range).

The transmitter 26 is thus capable of emitting very high frequency laser pulses. It is therefore connected to the computer 21 which controls the emission of these laser pulses.

The receiver 28 is in turn a photoreceptor cell adapted to capture the part of the light beam emitted by the transmitter 26 which is reflected by a possible stationary or moving obstacle.

This receiver 28 is connected to the computer 21 so as to provide it with information relating to the light flux that it receives.

The invention relates more particularly to the optical system 27, which comprises two distinct and different lenses.

The first lens, which is located on the side of the transmitter 26 and which is centered on the optical axis A1, is a biconical lens 27A. Such a biconical lens 27A has a different refractive power along two axes orthogonal to the optical axis A1.

This biconical lens 27A is here a convergent cylindrical lens, with a horizontal cylinder axis. In other words, it has a refractive power which is non-zero along a first axis (here the vertical axis) and which is zero along a second axis (here the horizontal axis which is perpendicular to the optical axis) .

Its function is to continuously and vertically overwrite the light beam emitted by the transmitter 26, so that the vertical angular field of this light beam is smaller at its exit from the biconical lens 27A than at its entry.

Otherwise formulated, it allows the light beam to be crushed so that it has a height (in the vertical plane) less than its width (in the horizontal plane).

The cylindrical power of this biconical lens 27A is determined so that, taking into account the distance between this lens and the emitter and taking into account the characteristics of this emitter 26, the vertical field of the light beam has an opening of between 5 and 15 degrees at its exit from the biconical lens 27A (it is here less than 10 degrees, and more precisely equal to 8 degrees).

The optical axis A1 is here placed horizontally. The light beam can thus be concentrated around a horizontal plane which is located above the road plane. In this way, the biconical lens 27A optimizes the detection of pedestrians, cars and other obstacles, without illuminating the road itself or the road signs located at height. This makes it easier to distinguish potentially dangerous obstacles from the road itself.

Here, the biconical lens 27A is made of plastic, and more precisely of PMMA (poly (methyl methacrylate)), so as to present a very reduced cost price.

It has a diameter strictly less than 12 mm, for example between 4 and 8 mm.

The second lens used is a spherical lens 27B which has an adjustable focal distance, capable of being controlled by the computer 21, so as to extend, if necessary, the detection range of the device (case of FIG. 2) or to widen the field. device detection (case of Figure 4).

The spherical lens 27B is here a liquid lens, that is to say a deformable lens containing a fluid.

This spherical lens 27B comprises a rigid capsule which has transparent, flat and circular front and rear walls around the optical axis A1. This capsule internally defines a housing for a conductive liquid and for a non-conductive liquid which is immiscible with the conductive liquid.

The spherical lens 27B also has a pair of electrodes. These electrodes are each annular in shape around the optical axis A1 to surround the liquid contained in the capsule. One of these electrodes is located on the side of the front wall of the capsule when the other electrode is placed on the side of the rear wall of this capsule.

The focal distance of the spherical lens 27B can then be controlled by an electrical control signal, for example a voltage applied between these two electrodes. Indeed, this electric voltage will have the effect of deforming the conducting liquid, so that the surface between the two liquids curves more or less and consequently modifies the focal distance of the spherical lens 27B.

The diameter of this spherical lens 27B is here preferably equal to 12 mm or less than 12 mm, so that the liquid is not very sensitive to gravity and that gravity therefore does not deform the surface between the two liquids.

The computer 21 is provided for controlling the electrical voltage across the electrodes of the spherical lens 27B and for processing the signals received from the receiver 28.

The computer 21 includes for this purpose a processor connected to the transmitter 26, to the spherical lens 27B, to the receiver 28, by means of alert 17, 18, and to a storage unit, for example a rewritable non-volatile memory or a hard drive.

The storage unit stores in particular data used within the framework of the method described below, in particular a mapping allowing it to know at all times the focal distance value to be applied to the spherical lens 27B.

The storage unit also stores a computer application, consisting of computer programs comprising instructions, the execution of which by the processor allows the computer 21 to implement the method described below.

The computer 21 is thus particularly suitable for developing, as a function of the data received from the obstacle detection device 20, a control signal to be sent to the alert means 17, 18, when this proves useful, in particular in the event of obstacle detected.

This alert means, which is not in itself the subject of the present invention, may take various forms.

As shown in Figure 1, it may be an audible warning device adapted to emit an audible warning signal of varying intensity or frequency, depending on the distance separating the vehicle from the detected obstacle.

It could also be a visual warning, such as a network of diodes adapted to emit a luminous flux of intensity and / or color varying according to the distance separating the vehicle from the detected obstacle.

It could also be a screen 17 adapted to display an alert message, or a vibrator which, placed in the seat or in the steering wheel of the vehicle, could emit vibrations of varying intensities or frequencies. , depending on the distance between the vehicle and the obstacle detected.

Still alternatively, the alert means may be formed by the computer 21 itself, in which case the alert signal emitted by the computer will be an electrical signal for controlling the system for controlling the direction of the vehicle and / or the braking system of the wheels 13 and / or of the powertrain 14. Thus, the computer can force, for example, the stopping of the acceleration of the engine when the obstacle is still far away and the braking of the vehicle when the obstacle is approaching.

Anyway, the object of the present invention is to use the spherical lens 27B so as to detect obstacles effectively.

According to the invention, the method for controlling the focal distance of the spherical lens 27B implemented by the computer 21 comprises three successive steps, namely:

- a step of determining a focal distance value,

a step for controlling the focal distance of the spherical lens 27B so that it has said value, then

- An impulse step during which said emitter 26 emits a light beam and during which the focal distance of the spherical lens 27B is controlled to remain constant.

The first determination step consists more precisely in determining the focal distance value which will allow the obstacle detection device 20 to detect the obstacles most likely to generate a risk for the motor vehicle 10.

As a first example, this focal distance value can be chosen as a function of the speed of the motor vehicle 10.

In fact, the faster the motor vehicle 10 travels, the lower the risk that the vehicle collides with obstacles situated at an angle to the vehicle. Thus, we can choose a focal length value that is much lower than the speed of the vehicle. The association between focal length value and speed can be predetermined and recorded in the map of the computer 21.

In this mapping, provision may be made for the focal distance value to be chosen also as a function of the orientation of the steered wheels of the motor vehicle 10.

Indeed, the emitter 26 here having a fixed orientation relative to the chassis of the motor vehicle 10, it will be possible to increase the value of focal distance of the spherical lens 27B when the motor vehicle rotates, so as to widen the light beam 22 in order to detect obstacles in the direction the vehicle is moving.

As a second example, we can determine the focal distance value to be applied to the spherical lens 27B as a function of the environment in which the motor vehicle 10 operates.

Thus, when numerous obstacles are detected by the obstacle detection device 20, which can mean that the vehicle is moving in built-up areas, provision may be made to increase the focal distance of the spherical lens 27B so as to detect the obstacles the closer to the vehicle.

Alternatively, one could use the on-board geolocation system in the motor vehicle 10 to determine whether the vehicle is in built-up areas, outside built-up areas, on expressways or on motorways. It will then be possible to adjust the focal length according to the type of lane the vehicle is traveling on.

As a third example, we can determine the focal distance value to be applied to the spherical lens 27B as a function of the distance separating the motor vehicle 10 from the detected obstacle.

Thus, if the detected obstacle is at a great distance and its detection has a low reliability, it will be possible to reduce the focal distance value so that the light beam focuses on the obstacle, which will verify that its detection is reliable.

The second step of controlling the focal distance of the spherical lens 27B consists, for the computer 21, of applying an electric voltage to the two electrodes of the spherical lens 27B which is a function of the value of focal length determined and which will allow the spherical lens 27B to present this focal distance value.

Thus, as shown in FIG. 2, when a high voltage is applied to the electrodes of the spherical lens 27B, the conductive liquid will bend with a small radius of curvature, which will make it possible to reduce the focal distance and to concentrate the light beam 22 on the optical axis A1. This provides a large obstacle detection range, but reduces the detection field.

FIG. 3 then illustrates the light intensity I (expressed in W / sr) as a function of the orientation Y (expressed in degrees) of the ray of light considered with respect to the optical axis A1, in a horizontal plane.

We observe that in a limited detection field between -5 and 5 degrees, this light intensity is very high, which ensures a long range of obstacle detection.

We also observe that between -8 and -5 degrees and between 5 and 8 degrees, this detection range is considerably reduced.

Finally, we observe that no obstacle can be detected outside the detection field between -8 and 8 degrees.

Conversely, as shown in Figure 4, when a low or zero voltage is applied to the electrodes of the spherical lens 27B, the conductive liquid will flatten or bend slightly with a large radius of curvature, which will allow little or no focusing of the light beam 22. This ensures a large obstacle detection field, but reduces the detection range.

FIG. 5 then illustrates the light intensity I (expressed in W / sr) as a function of the orientation Y (expressed in degrees) of the ray of light considered with respect to the optical axis A1, in the horizontal plane.

It is observed that in a wide detection field between -20 and 20 degrees, the light intensity is sufficiently high to ensure the detection of an obstacle located near the vehicle. The detection range is of course lower than in the case of FIG. 3, but it is sufficient in the case where the vehicle is traveling at low speed since this application does not require a large range at the edge of the detection field.

The third pulse step, during which the emitter 26 is controlled by the computer 21 to emit a laser pulse (corresponding to the light beam 22), is out of phase and synchronized with the previous step.

It will be preferred that the focal length value of the spherical lens 27B remains invariable when the emitter 26 emits the light beam 22.

Although this is not necessarily necessary, here, the control of the focal distance value of the spherical lens 27B is synchronized with the frequency of the laser pulses emitted by the transmitter 26. This frequency can for example be of the order of 100 kHz.

Finally, when the computer 21 receives the data from the receiver 28, it is able to determine the possible proximity of an obstacle, so as to send a control signal if necessary to the alert means 17, 18, so that that this informs the driver of the presence of this obstacle or so that it controls the deceleration or braking of the motor vehicle 10.

The present invention is in no way limited to the embodiment described and shown.

Thus, by way of example, provision could be made to use a lens having a non-zero prismatic power for deflecting the light beam.

According to another alternative embodiment of the invention, the device could be used not to detect only an obstacle, but more generally any object located in the environment of the motor vehicle. Thus, by way of an illustrative example, this device could be installed on the side or at the rear of the vehicle where it will, for example, make it possible to detect a vehicle traveling in a traffic line parallel to that used by the vehicle. In this way, the device will make it possible to check whether or not the vehicle can change the traffic line without danger.

According to another alternative embodiment of the invention, the spherical lens used could be a lens of a different type from that described above.

Thus, it could be a lens with a deformable membrane. Such a lens is for example marketed under the brand "Optotune" or "Holochip". It has a cylindrical housing, the end faces of which are transparent and which houses a thin membrane of flexible polymer immersed in a liquid.

To modify the shape of the membrane (in order to achieve focusing), it is then possible to use a circular ring located against the membrane, and to control it in position to mechanically deform the membrane.

It is also possible to manufacture the membrane in an electro-active polymer (that is to say which has the particularity of being deformed under the effect of an electric field). By applying an electric field to the membrane, it is thus possible to modify its radius of curvature and therefore the focal distance.

Any other type of lens with adjustable focal length may also be used.

Claims (10)

1. Object detection device (20) for a motor vehicle (10), comprising: - a transmitter (26) adapted to emit a light beam (22), - an optical system (27) which comprises a spherical lens (27B) with adjustable focal distance, adapted to focus the light beam (22) leaving the emitter (26), - a receiver (28) adapted to receive part of the light beam (22) after it has been reflected by an object, and - means for controlling (21) the focal distance of the spherical lens (27B), characterized in that said optical system (27) also comprises a biconical lens (27A) which is located between the emitter (26) and the spherical lens (27B) and which has a diameter strictly smaller than that of the spherical lens (27B). 2. Object detection device (20) according to the preceding claim, wherein said biconical lens (27A) having an optical axis and a first and a second axis perpendicular to each other and perpendicular to the optical axis, the lens biconical (27A) has a non-zero optical power along the first axis and a zero optical power along the second axis. 3. Object detection device (20) according to one of the preceding claims, in which said biconical lens (27A) has a cylindrical optical power and a distance from the emitter (26) such as the light beam (22) has, at its exit from the biconical lens (27A), an opening angle of between 5 and 15 degrees in a plane which includes an optical axis of the biconical lens (27A) and which is perpendicular to a first orientation axis of the cylindrical optical power of the biconical lens (27A). 4. Object detection device (20) according to one of the preceding claims, wherein said biconical lens (27A) is made of plastic. 5. Object detection device (20) according to one of the preceding claims, wherein said spherical lens (27B) has a diameter less than 12 mm. 6. Device for detecting objects (20) according to one of the preceding claims, in which said spherical lens (27B) comprises, on the one hand, a capsule which internally delimits a housing for a conductive liquid, and, on the other hand, at least one pair of electrodes. 7. Object detection device (20) according to the preceding claim, wherein said control means (21) are adapted to control the electrical voltage across said electrodes. 8. Object detection device (20) according to one of the preceding claims, wherein said transmitter (26) comprises at least one diode. 9. Method for controlling the focal length of a spherical lens (27B) of an object detection device (20) according to one of the preceding claims, in which it is provided: - a step of determining a focal distance value, - a step of controlling the focal distance of the spherical lens (27B) so that it has said value, then - an impulse step during which said emitter (26) emits a light beam and during which the focal distance of the spherical lens (27B) is controlled to remain invariable. 10. Control method according to the preceding claim, in which, in the determination step, said value is determined as a function of at least one of the following parameters: - speed of the motor vehicle (10), - orientation of the steering wheels of the motor vehicle (10), - distance separating the motor vehicle (10) from said obstacle, - environment of the motor vehicle (10).