Thermal imaging capture system

Abstract

A thermal imaging capture system is proposed comprising: - a housing (110) defining a first aperture, - a window (120) configured to at least partially cover the first aperture, 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 aperture. The window, the first aperture, and the second aperture are positioned to allow external radiation to pass to the sensor. According to the invention, the thermal imaging capture system includes a thermal interface (140) positioned to be in contact with the window and with the capture device, said thermal interface defining a third aperture configured to allow said external radiation to pass to the sensor and to define, with the window and the capture device, a sealed space containing a gas layer.Figure for the abridged version: 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 case defining a first opening, - a pane of glass configured to at least partially cover the first opening, and - a capture device positioned inside the casing and comprising a sensor and an outer casing, the outer casing housing the light sensor and defining a second aperture, and in which 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 purpose, a thermal camera is generally used. Such a camera usually operates in the infrared and allows the temperature emitted by the various objects observed to be measured.

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

[0007] The presence of the glass in front of the thermal camera will however lead to measurement errors induced on the one hand by the absorption and reflection of part of the infrared rays to be measured and the influence of the temperature of the glass on the measurements carried out, but also by internal reflections on the glass 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 glass in order to homogenize the glass temperature and thus improve its calculation. Furthermore, as explained below, it is proposed to correct measurement errors caused by the presence of the glass through the accurate estimation of the glass temperature thus obtained.

[0009] More particularly, the invention proposes 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 glass and in contact with the capture device, said thermal interface defining a third opening configured to allow said external radiation to pass to the sensor and to define with the glass and the capture device a sealed space containing a gas layer.

[0010] Thus, thanks to the invention, the glass is in thermal contact with the sensor in such a way as to minimize the temperature difference between the sensor and the glass. Furthermore, the airtight gas layer between the glass and the sensor helps to homogenize the temperature of the glass. This gas layer makes it easier to estimate the temperature of the glass and to more easily account for temperature measurement errors caused by the presence of the glass, without the need for an additional sensor.

[0011] According to one embodiment, the thermal interface (made for example in the form of a part having two principal directions of extension and a thickness extending perpendicularly to these two principal directions of extension) can be composed of a material having a thermal conductivity greater than or equal to 3.3 Wm'.K1 for each millimeter of thickness.

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

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

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

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

[0016] In addition, the calculation of the corrected temperature of a pixel may include a correction of the errors caused by the presence of the glass.

[0017] In addition, the control unit can be configured to memorize at least one area of ​​interest from the captured image.

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

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

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

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

[0022] The thermal interface can 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 can be at least partially metallic.

[0025] The different features, variants and embodiments of the invention can be combined with each other in various ways insofar as they are not incompatible or mutually exclusive. Brief description of the figures

[0026] In addition, various other features of the invention become apparent from the attached description made with reference to the drawings which illustrate non-limiting embodiments of the invention and where:

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

[0028] [Fig.2] is a schematic perspective representation of the thermal image capture system of [Fig.1], and

[0029] [Fig.3] is a schematic representation of an image calculated by the control unit of the thermal image capture system of [Fig.1].

[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 schematically represented in Figures 1 and 2 and designated as a whole by 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 cross-section on [Fig.1] and in perspective on [Fig.2].

[0033] The image capture system 100 is for example positioned in a motor vehicle and allows a thermal image of the vehicle's interior to be captured.

[0034] Preferably, the image capture system 100 is placed in the ceiling of the vehicle's passenger compartment and allows observation of the two rows of seats in the vehicle, their passengers, and the vehicle's windows.

[0035] The housing 110 defines a first opening. The first opening is rectangular here. 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 for more uniform temperatures of the components positioned inside said housing 110.

[0037] The glass 120 covers at least in part (here in full) the first opening.

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

[0039] The window 120 is preferably opaque in the visible and allows the interior of the housing 110 to be hidden from the passengers of the vehicle.

[0040] To minimize reflections, the glass 120 may also include an anti-reflective coating. In this case, the anti-reflective treatment is configured to be active particularly in the wavelengths captured by the capture device 130. Here, the anti-reflective treatment facilitates transmission in the infrared.

[0041] The capture device 130 is positioned inside the housing 110 and includes 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 efficiently as possible.

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

[0045] The capture device 130 may also include a lens configured to image the vehicle's interior on the sensor 131.

[0046] The thermal interface 140 allows the window 120 and the capture device 130 to be brought 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 maximizes the thermal contact between the capture device 130 and the glass 120. This thermal contact minimizes the temperature difference between the glass 120 and the capture device 130.

[0050] The thermal interface 140, the glass 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 layer contained within the sealed space allows the temperature of the window 120 to be homogenized over its entire surface. Thus, a single temperature can be estimated for the entire window 120.

[0052] Furthermore, the sealed enclosure protects the capture device 130. Indeed, the thermal imaging capture system 100 is preferably mounted in a clean environment. Since the enclosure is 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 glass 120.

[0054] The thermal interface 140 is preferably made of a flexible material that can adapt to the tolerances of the assembly of the thermal image capture system 100.

[0055] The thermal interface 140 can be composed of a thermal pad (for example, of the type “Bergquist”, registered trademark, “Gap Pad VO Ultra Soft” with a thickness of 1 mm), a non-hardening thermal paste (for example, of the type “DOWSIL”, registered trademark, TC-5622 “Thermally Conductive Compound”) or a thermal interface film (for example, of the type “Nitto”, registered trademark, EST-805(DL) with a thickness of 50 sqm, 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 principal directions of extension (perpendicular to each other) and a thickness extending perpendicularly to these two principal 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 can be made of silicone.

[0059] Alternatively, the thermal interface 140 may comprise several layers of different materials. The different material layers then allow heat to be conducted.

[0060] The thermal interface 140 is adhesive here and allows the glass 120 to be fixed to the thermal image capture system 100. In other words, the glass 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 configured here to capture an image (here a thermal image). The captured image is a pixel matrix, for example a 32x24 matrix. Alternatively, the captured image may be 16x12 in size.

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

[0064] For example, the sensor 131 includes a thermopile and a thermistor for each pixel. The sensor 131 here includes a computer that measures electrical quantities (in particular the voltage of the thermopiles) and provides, 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 within the solid angle of measurement of the pixel, and the temperature of the hot junction is related to the temperature received by the pixel.

[0065] The thermopile voltage indicates 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 sums 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 includes a control unit 150. The control unit 150 is configured to receive the captured image.

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

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

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

[0071] Since the gas layer 200 is temperature homogeneous thanks to the thermal interface 140, it allows the window 120 to remain temperature homogeneous. Thus, only one window temperature needs to be estimated, regardless of the location on 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 ATc 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 ATc, which can be considered constant. The temperature difference ATc is established through experimental measurements during the design of the thermal imaging capture system 100.

[0076] A corrected temperature TCûrr is defined as the temperature corresponding to the measured temperature corrected for measurement errors, that is, 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 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 vitre 130.

[0077] The thermal absorption coefficient α takes into account, in particular, the internal absorption of the glass 130, corresponding to the absorption of infrared waves by the glass. Furthermore, the thermal absorption coefficient α takes into account reflections of infrared waves on the external surface of the glass 130.

[0078] The control unit 150 can be configured to calculate a corrected image 152. The corrected image 152 can include 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 include 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 in the captured image. This 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 within the vehicle's interior considered important to monitor in order to improve passenger thermal comfort.

[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 at least one area of ​​interest. For example, the temperature representative of at least one area of ​​interest can be defined as the average of the corrected temperatures of the pixels belonging to at least one area of ​​interest.

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

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

[0086] Alternatively, the control unit 150 can be configured to control the vehicle's air conditioning system based on 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 represented, but a person skilled in the art will be able to make any variation in accordance with the invention.

Claims

Demands

1. Thermal image capture system (100) comprising: - a housing (110) defining a first aperture, - a window (120) configured to at least partially cover the first aperture, - 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 aperture, the window (120), the first and second apertures 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 glass (120) and the capture device (130) a sealed space containing a gas layer (200).

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

5. Thermal image capture system (100) according to any 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. Thermal image capture system (100) according to claim 5, wherein the control unit (150) is configured to calculate a corrected temperature on at least one pixel.

7. Thermal image capture system (100) according to claim 6, wherein the calculation of the corrected temperature of a pixel includes a correction of errors caused by the presence of the glass (120).

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

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

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

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

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