Thermal image capture system

Abstract

A thermal image capture system is proposed comprising: - a housing (110) defining a first opening, - a window (120) configured to at least partially cover the first opening, and - a capture device (130) positioned inside the housing and comprising a sensor (131) and an outer casing (132), the outer casing housing the sensor and defining a second opening. The window, the first opening and the second opening are positioned so as to allow external radiation to pass towards the sensor. According to the invention, the thermal image capture system comprises a thermal interface (140) positioned to be in contact with the window and in contact with the capture device, said thermal interface defining a third opening configured to allow said external radiation to pass towards the sensor and to define with the window and the capture device a sealed space containing a gas layer.Figure for abstract: Fig. 1.

Description

Title of the invention: Thermal image capture system Technical field

[0001] The present invention relates to the technical field of infrared imaging.

[0002] The invention relates more particularly to a thermal image capture system comprising: - a box defining a first opening, - a window configured to at least partially cover the first opening, and - a capture device positioned inside the housing and comprising a sensor and an outer casing, the outer casing housing the light sensor and defining a second opening, and wherein the glass, the first opening and the second opening are positioned so as to allow external radiation to pass towards the sensor.

[0003] The invention finds a particularly advantageous application in the thermal control of vehicles. Technological background

[0004] In order to optimize passenger comfort while optimizing the energy expenditure of a motor vehicle, it is common to control the temperature distribution in the vehicle.

[0005] For this, a thermal camera is generally used. Such a camera generally operates in the infrared and makes it possible to measure the temperature emitted by the different objects observed.

[0006] For aesthetic reasons and to protect the camera, it may be useful to place an opaque window in front of the camera. The camera is then invisible to the passengers.

[0007] The presence of the window in front of the thermal camera will however lead to measurement errors induced on the one hand by the absorption and reflection of a part of the infrared rays to be measured and the influence of the temperature of the window on the measurements carried out, but also by internal reflections on the window of the infrared radiation emitted by the thermal camera. Summary of the invention

[0008] In this context, the present invention proposes to maximize the thermal contact between the sensor and the window in order to homogenize the temperature of the window and to be able to calculate it better. It is then further proposed, as explained below, to correct the measurement errors induced by the presence of the window thanks to the correct estimation of the temperature of the window thus carried out.

[0009] More particularly, according to the invention, there is proposed a thermal image capture system as defined in the introduction, in which a thermal interface is provided, said thermal interface being positioned to be in contact with the window and in contact with the capture device, said thermal interface defining a third opening configured to allow said external radiation to pass towards the sensor and to define with the window and the capture device a sealed space containing a gas layer.

[0010] Thus, thanks to the invention, the window is in thermal contact with the sensor so as to minimize the temperature difference between the sensor and the window. In addition, the sealed gas blade between the window and the sensor makes it possible to homogenize the temperature of the window. This gas blade makes it easier to estimate the temperature of the window, and to be able to take into account more easily and without adding an additional sensor the temperature measurement errors induced by the presence of the window.

[0011] According to one embodiment, the thermal interface (produced for example in the form of a part having two main directions of extension and a thickness extending perpendicular to these two main directions of extension) can be composed of a material having a thermal conductivity greater than or equal to 3.3 Wm '.K 1 for each millimeter of thickness.

[0012] Furthermore, the thermal interface may be made of a flexible material.

[0013] In addition, the glass can be bonded to the thermal interface.

[0014] The sensor may be configured to capture an image comprising pixels. The value of each pixel may correspond to a measured temperature of the radiation received on said pixel. The thermal image capture system may further comprise a control unit configured to receive the captured image.

[0015] The control unit may be configured to calculate a corrected temperature on at least one pixel.

[0016] Furthermore, the calculation of the corrected temperature of a pixel may include a correction of the errors generated by the presence of the glass.

[0017] Additionally, the control unit may be configured to store at least one area of ​​interest of the captured image.

[0018] The at least one area of ​​interest may comprise at least two pixels.

[0019] The control unit may also be configured to calculate at least one temperature representative of the at least one area of ​​interest.

[0020] On the other hand, the sensor can be an infrared thermal sensor.

[0021] Further, the sensor may include at least one thermopile device.

[0022] The thermal interface may be in contact with the external housing.

[0023] In addition, the glass may include an anti-reflective coating in the infrared.

[0024] Also, the outer casing may be at least partially metallic.

[0025] The various features, variants and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive. Brief description of the figures

[0026] Furthermore, various other characteristics of the invention emerge from the appended description given with reference to the drawings which illustrate non-limiting forms of embodiment of the invention and where:

[0027] [Fig-1] is a schematic cross-sectional representation of a thermal image capture system according to one embodiment of the invention,

[0028] [Fig.2] is a schematic perspective representation of the thermal image capture system of [Fig.l], and

[0029] [Fig.3] is a schematic representation of an image calculated by the control unit of the thermal image capture system of [Fig.l].

[0030] It should be noted that in these figures the structural and / or functional elements common to the different variants may have the same references. Detailed description

[0031] A thermal image capture system according to the invention, as shown schematically in FIGS. 1 and 2 and designated as a whole by the reference 100, comprises a housing 110, a window 120, a capture device 130 and a thermal interface 140.

[0032] The image capture system 100 is shown in section in [Fig. 1] and in perspective in [Fig. 2].

[0033] The image capture system 100 is for example positioned in a motor vehicle and makes it possible to capture a thermal image of the passenger compartment of the vehicle.

[0034] Preferably, the image capture system 100 is placed in the ceiling of the passenger compartment of the vehicle and makes it possible to observe the two rows of seats of the vehicle, their passengers as well as the windows of the vehicle.

[0035] The housing 110 defines a first opening. The first opening is here rectangular. Alternatively, the first opening could take any shape. For example, the first opening could be circular.

[0036] The housing 110 is for example made of plastic (such as polybutylene terephthalate), possibly reinforced with glass fibers. Alternatively, the housing 110 could be metallic in order to further improve heat conduction and to allow the temperatures of the components positioned inside said housing 110 to be homogenized.

[0037] The window 120 covers at least partially (here entirely) the first opening.

[0038] The glass here is composed of a monocrystalline silicon blade. Alternatively, the glass could be made of another material transparent to the radiation concerned (here infrared), such as germanium, zinc selenide, in a "chalcogenide" type glass, or in an organic glass of the acrylic or polycarbonate type.

[0039] The window 120 is preferably opaque in the visible and makes it possible to hide the interior of the housing 110 from the passengers of the vehicle.

[0040] To minimize reflections, the window 120 may also include an anti-reflective coating. The anti-reflective treatment is in this case configured to be active in particular in the wavelengths captured by the capture device 130. Here, the anti-reflective treatment makes it possible to facilitate transmission in the infrared.

[0041] The capture device 130 is positioned inside the housing 110 and comprises a sensor 131 and an outer casing 132. The sensor 131 is positioned inside the outer casing 132.

[0042] The outer casing 132 defines a second opening. The second opening is here circular. Alternatively, the second opening can be of any shape, for example rectangular.

[0043] The outer casing 132 is at least partially metallic. Preferably, it is entirely metallic, in order to conduct heat as well as possible.

[0044] The window 120, the first opening and the second opening are positioned (here aligned) so as to allow external radiation to pass through to the thermal image capture system 100 towards the sensor 131.

[0045] The capture device 130 may also comprise a lens configured to image the vehicle interior onto the sensor 131.

[0046] The thermal interface 140 makes it possible to bring the window 120 and the capture device 130 into contact. The thermal interface 140 is for example in the form of a plate which extends along the window 120.

[0047] The thermal interface 140 defines a third opening. The third opening is preferably circular. Alternatively, the third opening may have another shape, for example rectangular.

[0048] The third opening is configured to allow external radiation to pass towards the sensor 131.

[0049] The thermal interface 140 makes it possible to maximize the thermal contact between the capture device 130 and the window 120. This thermal contact makes it possible to minimize the temperature difference between the window 120 and the capture device 130.

[0050] The thermal interface 140, the window 120 and the capture device 130 form a sealed space containing a gas layer. The gas layer is delimited by the third opening of the thermal interface.

[0051] The gas blade contained in the sealed space makes it possible to homogenize the temperature of the window 120 over its entire surface. Thus, a single temperature can be estimated for the entire window 120.

[0052] In addition, the sealed space makes it possible to protect the capture device 130. Indeed, the mounting of the thermal image capture system 100 is preferably carried out in a clean atmosphere. The space being sealed, no dust can enter it after mounting.

[0053] Preferably, and in order to maximize heat dissipation, the thermal interface 140 is in contact with the external housing. The thermal interface 140 is for example interposed between the external housing 110 and the window 120.

[0054] The thermal interface 140 is preferably composed of a flexible material capable of adapting to the tolerances of the assembly of the thermal image capture system 100.

[0055] The thermal interface 140 may be composed of a thermal pad (for example of the “Bergquist” type, registered trademark, “Gap Pad VO Ultra Soft” with a thickness of 1 mm), a non-hardening thermal paste (for example of the “DOWSIL” type, registered trademark, TC-5622 “Thermally Conductive Compound”) or a thermal interface film (for example of the “Nitto” type, registered trademark, EST-805(DL) with a thickness of 50 μm, the low thickness of which compensates for the low thermal conductivity).

[0056] The thermal interface 140 is composed of a heat-conducting material. The thermal interface 140 has, for example, a general plate shape, with two main directions of extension (perpendicular to each other) and a thickness extending perpendicular to these two main directions of extension.

[0057] Preferably, the thermal interface 140 is composed of a material having a thermal conductivity greater than or equal to 3.3 Wm *.K1 for each millimeter of thickness.

[0058] For example, the thermal interface 140 may be made of silicone.

[0059] Alternatively, the thermal interface 140 may comprise several layers of different materials. The different layers of materials then make it possible to conduct heat.

[0060] The thermal interface 140 is here adhesive and makes it possible to fix the window 120 to the thermal image capture system 100. In other words, the window 120 is glued to the thermal interface 130.

[0061] The sensor 131 is here a thermal sensor operating in the infrared. Preferably, the sensor 131 is sensitive to wavelengths between 7 and 14 micrometers.

[0062] The sensor 131 is here configured to capture an image (here a thermal image). The captured image is a matrix of pixels, for example a matrix of dimensions 32x24. Alternatively, the captured image may be of dimensions 16x12.

[0063] The sensor here comprises at least one thermopile device.

[0064] For example, the sensor 131 comprises a thermopile and a thermistor for each pixel. The sensor 131 here comprises a computer which makes it possible to measure the electrical quantities (in particular the voltage of the thermopiles) and delivers for each pixel information representing the temperature of the cold junction of the corresponding thermopile (reference temperature measured by the thermistor) and information representing the temperature of the hot junction of the corresponding thermopile. The hot junction of the corresponding thermopile is influenced by the infrared radiation received in the solid measurement angle of the pixel, and the temperature of the hot junction has a link with the temperature received by the pixel.

[0065] The thermopile voltage is indicative of the difference between the cold junction temperature and the hot junction temperature (which corresponds to the temperature radiated by objects located in the pixel's detection field). To obtain the hot junction temperature, the computer calculates the sum of the cold junction temperature (measured by the thermistor) and the difference (measured by the thermopile). The temperature Tm measured by each pixel can then be determined as a function of the hot junction temperature for that pixel (based on a physical model of the sensor in question).

[0066] The computer can then define the captured image by assigning to each pixel a value corresponding to the temperature measured by the pixel as described above.

[0067] The thermal image capture system 100 further comprises a control unit 150. The control unit 150 is configured to receive the captured image.

[0068] The control unit 150 is here configured to calculate a corrected image 152 using the captured image. The calculation of the corrected image 152 includes a correction of the errors generated by the presence of the window.

[0069] Indeed, the presence of the window 120 induces measurement errors due in particular to the reflection of the infrared waves emitted by the sensor 131 on the internal face of the window 120 towards the sensor 131. In other words, the sensor 131 risks measuring its own temperature because of the reflections on the internal face of the window 120.

[0070] Furthermore, the presence of the window 120 induces measurement errors due to the emission by the window 120 of its own temperature. To estimate these errors and compensate for them, it may be useful to know the temperature of the window 120.

[0071] The gas blade 200 being homogeneous in temperature thanks to the thermal interface 140, it makes it possible to keep the window 120 homogeneous in temperature. Thus, a single window temperature is to be estimated, independently of the location of the window 120 considered.

[0072] The temperature of the glass is approximated to the temperature of the gas blade 200.

[0073] The temperature of the gas blade 200 can be estimated using the equation: TC = TPF- ATc where Tc is the temperature of the gas blade 200, TPF is the temperature of the focal point of the capture device 130, and A Tc is the temperature difference between the focal plane of the capture device 130 and the gas blade 200.

[0074] The temperature of the focal point TPF is measured here using a thermal sensor integrated into the capture device 130.

[0075] The good thermal coupling between the gas blade 200 and the capture device 130 creates a stable temperature difference A Tc which can be considered as a constant. The temperature difference A Tc is established through experimental measurements during the design of the thermal image capture system 100.

[0076] A corrected temperature TCûrr is defined as the temperature corresponding to the measured temperature corrected for measurement errors, i.e. the estimated temperature of the objects observed by a pixel. The corrected temperature Tcorr can be calculated using the temperature measured Tm by the capture device 130 and by the temperature of the gas blade Tc. Indeed, the corrected temperature Tcorr is calculated using the equation: / F, \ { where a is the thermal absorption coefficient of the Tcorr — \ J window 130.

[0077] The thermal absorption coefficient a takes into account in particular the internal absorption of the window 130 corresponding to the absorption of infrared waves by the window. In addition, the thermal absorption coefficient a takes into account reflections of infrared waves on the external face of the window 130.

[0078] The control unit 150 may be configured to calculate a corrected image 152. The corrected image 152 may comprise a corrected temperature value for each pixel. An example of a corrected image 152 is shown in [Fig.3].

[0079] Alternatively, the corrected temperatures are not calculated for each pixel and the corrected image 152 may comprise at least one corrected temperature value on at least one pixel.

[0080] Preferably, the control unit 150 is configured to store at least one area of ​​interest of the captured image. The at least one area of ​​interest is a grouping of pixels comprising at least two pixels. The at least one area of ​​interest can be defined according to the locations of the vehicle interior considered to be of interest to monitor in order to improve the thermal comfort of the passengers.

[0081] For example, areas of interest can be defined on vehicle windows and on the heads of vehicle passengers. Here, thirty areas of interest are defined.

[0082] In practice the number of defined areas of interest can vary from 2 areas to 100 areas, for example.

[0083] The control unit 150 is configured here to calculate at least one temperature representative of the at least one area of ​​interest. For example, the temperature representative of the at least one area of ​​interest may be defined as the average of the corrected temperatures of the pixels belonging to the at least one area of ​​interest.

[0084] The control unit 150 may also be configured to calculate the minimum temperature and the maximum temperature of the at least one area of ​​interest. The minimum temperature may be defined as the smallest temperature of the corrected temperatures of each pixel. The maximum temperature may be defined as the largest temperature of the corrected temperatures of each pixel.

[0085] The control unit 150 is here configured to send information to a computer network internal to the vehicle. For example, the control unit 150 can send the calculated temperature values ​​to another control unit.

[0086] Alternatively, the control unit 150 may be configured to control the vehicle's air conditioning system based on the calculated temperature values ​​and with the aim of optimizing the thermal comfort of the passengers.

[0087] The present invention is in no way limited to the embodiment described and shown, but those skilled in the art will be able to provide any variant in accordance with the invention.

Claims

Claims

1. A thermal image capture system (100) comprising: - a housing (110) defining a first opening, - a window (120) configured to at least partially cover the first opening, - a capture device (130) positioned inside the housing (110) and comprising a sensor (131) and an outer casing (132), the outer casing (132) housing the sensor (131) and defining a second opening, the window (120), the first opening and the second opening being positioned so as to allow external radiation to pass towards the sensor (131), the image capture system (100) being characterized in that it comprises a thermal interface (140) positioned to be in contact with the window (120) and in contact with the capture device (130),said thermal interface (140) defining a third opening configured to allow said external radiation to pass towards the sensor (131) and to define with the window (120) and the capture device (130) a sealed space containing a gas blade (200).,

2. The thermal image capture system (100) of claim 1, wherein the thermal interface (140) is composed of a material having a thermal conductivity greater than or equal to 3.3 Wm *.K1 for each millimeter of thickness.

3. A thermal image capture system (100) according to one of claims 1 to 2, wherein the thermal interface (140) is composed of a flexible material.

4. Thermal image capture system (100) according to one of claims 1 to 3, wherein the glass (120) is bonded to the thermal interface (130).

5. The thermal image capture system (100) of one of claims 1 to 4, wherein the sensor (131) is configured to capture an image comprising pixels, the value of each pixel corresponding to a measured temperature of the radiation received on said pixel and the thermal image capture system (100) further comprising a control unit (150) configured to receive the captured image.

6. The thermal image capture system (100) of claim 5, wherein the control unit (150) is configured to calculate a corrected temperature on at least one pixel.

7. The thermal image capture system (100) of claim 6, wherein calculating the corrected temperature of a pixel includes correcting for errors caused by the presence of the glass (120).

8. A thermal image capture system (100) according to one of claims 5 to 7, wherein the control unit (150) is configured to store at least one area of ​​interest of the captured image, the at least one area of ​​interest comprising at least two pixels and the control unit (150) being configured to calculate at least one temperature representative of the at least one area of ​​interest.

9. A thermal image capture system (100) according to one of claims 1 to 8, wherein the sensor (131) is an infrared thermal sensor.

10. A thermal image capture system (100) according to one of claims 1 to 9, wherein the sensor (131) comprises at least one thermopile device.

11. A thermal image capture system (100) according to one of claims 1 to 10, wherein the thermal interface (140) is in contact with the housing (110).

12. Thermal image capture system (100) according to one of claims 1 to 11, wherein the glass (120) comprises an anti-reflective coating in the infrared.

13. A thermal image capture system (100) according to one of claims 1 to 12, wherein the outer casing (132) is at least partially metallic.

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