Unit for heat treatment of preforms comprising anti-radiation exposure safety systems
An image-based safety system in heat treatment units addresses radiation exposure risks by detecting removable walls and leakage, ensuring safe operation without additional sensors.
Patent Information
- Application Number
- CN202410741218.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-06-12
- Filing Date
- 2024-06-11
- Publication Date
- 2024-12-13
AI Technical Summary
Existing heat treatment units using monochromatic or pseudo-monochromatic electromagnetic radiation emitters pose a risk of radiation exposure to operators due to invisible infrared radiation leakage, necessitating cumbersome and expensive proximity sensors for safety, which are prone to human error.
A heat treatment unit equipped with an image acquisition device and processing system to detect the presence of removable walls and radiation leakage, ensuring safe operation by preventing start-up if walls are missing or radiation is detected.
Ensures reliable and efficient safety checks for removable walls and radiation leakage without the need for additional costly sensors, allowing safe operation of the heat treatment unit.
Smart Images
Figure CN119120842A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a heat treatment unit for heat treating preforms of a container manufacturing device, the heat treatment unit comprising a shell, the preforms travelling along a predetermined path in the shell, the heat treatment unit further comprising at least one emitting wall, the emitting wall comprising at least one emitting element for emitting monochromatic or pseudo-monochromatic electromagnetic radiation, the emitting element being arranged to emit radiation to the preforms passing through the shell, the shell being at least partially enclosed by at least one removable wall, the removable wall being arranged to prevent radiation from passing through the removable wall to the outside of the shell, the removable wall being arranged in a predetermined area of the shell. Background Art
[0002] Such a heat treatment unit or furnace is usually equipped with a plurality of heating elements which are arranged to emit heat in the direction of the synthetic material preforms travelling in the heat treatment unit in order to impose a heating profile on these preforms and to allow their subsequent deformation, for example by stretch blow moulding, in order to produce containers from the preforms.
[0003] The use of emitting elements or laser emitters emitting monochromatic or pseudo-monochromatic electromagnetic radiation as heating elements is particularly advantageous in such a heat treatment unit, since such elements offer higher efficiency and optical precision than other types of heating elements, such as halogen incandescent lamps, which allows faster and more selective heating of the preforms.
[0004] However, the use of such laser emitters must be accompanied by special precautions, since the emitted radiation is dangerous for operators moving around the thermal treatment unit. In fact, the radiation is emitted in the infrared range, invisible to the naked eye, and can therefore easily cause serious damage not only to the eyes but also to the skin of the operator, without the operator necessarily being aware that they are exposed to this radiation.
[0005] To prevent this exposure, it is proposed to confine the enclosure in which the preforms travel as much as possible, so as to limit the radiation leakage outside the enclosure to the greatest extent possible. To this end, it is proposed, for example, to close the enclosure with some walls arranged to block the passage of radiation, these walls enclosing the enclosure and the emitting element, while leaving at least one opening for the preforms to enter and exit the enclosure. At least some of these walls are removable, so as to leave access to the enclosure for loading and unloading and other operations when the thermal treatment unit is stopped and the emitting element is not emitting radiation.
[0006] Therefore, before any heat treatment unit is put into use, it should be ensured that all removable walls exist to avoid radiation leakage at these walls. The operator is usually responsible for checking that all removable walls do exist before allowing the heat treatment unit to be started. However, this inspection may be wrong and the operator may forget. Alternatively, it can be provided that the heat treatment unit is equipped with a proximity sensor between each removable wall and the support of these walls to physically detect the existence of these walls, and the proximity sensor is for example an optical, magnetic, inductive or mechanical type. This sensor is for example arranged to prevent the heat treatment unit from starting and / or issuing a warning when one of the walls does not exist. However, this equipment is particularly expensive and cumbersome to install and maintain because it requires as many sensors as the removable walls. Summary of the invention
[0007] One of the objects of the present invention is to overcome these drawbacks by proposing a thermal treatment unit the housing of which is closed in a reliable and easily inspectable manner.
[0008] To this end, the invention relates to a thermal treatment unit of the above-mentioned type, which also includes at least one safety system, the safety system including at least one image acquisition device and at least one processing device, the image acquisition device is oriented towards a predetermined area and the processing device is used to process the image acquired by the image acquisition device, the image acquisition device is arranged to acquire at least one image of the predetermined area, and the processing device is configured to detect whether the removable wall is present in the acquired image.
[0009] By using an image acquisition device to determine the presence or absence of a removable wall, it is possible to simply check whether the thermal treatment unit can be used safely and without risk, without requiring special installations on the enclosure itself. Furthermore, the same image acquisition device can be used to check the presence of a large number of removable walls based on a single acquired image. By selecting a suitable image acquisition device, it is also possible to check whether there is radiation leakage outside the enclosure based on the acquired image, thereby ensuring that the enclosure confinement is correctly achieved in the presence of all provided removable walls.
[0010] The heat treatment unit according to the invention may also include one or more of the following features, considered alone or in any combination that is technically feasible:
[0011] - the removable wall comprises at least one identification element, the image acquisition device is arranged to acquire at least one image of the identification element, the processing device being configured to detect whether the identification element is present in the acquired image;
[0012] - the image acquisition means comprises at least one camera, the camera capturing images in at least the visible light range, the camera being oriented such that at least the predetermined area extends within the range of the camera;
[0013] - the housing is at least partially closed by a plurality of adjacent removable walls, each removable wall extending over a predetermined area, the image acquisition device being arranged to acquire at least one image of all the predetermined areas, so that the processing device detects the presence or absence of all the removable walls based on the at least one single image acquired by the image acquisition device;
[0014] - the image acquisition device further acquires images in the near infrared range, the images acquired by the image acquisition device being capable of showing radiation emitted into the predetermined area, the processing device being arranged to identify the presence of radiation leakage out of the housing if at least one image acquired by the image acquisition device shows radiation emitted into the predetermined area;
[0015] - the thermal treatment unit further comprises at least one opening to the housing for passing the preforms into or out of the housing, at least one removable wall defining at least a portion of the opening;
[0016] - at least one removable wall extends in a transverse direction substantially perpendicular to the longitudinal direction towards the emitting element;
[0017] the housing is defined by two emitting walls in a transverse direction substantially perpendicular to the longitudinal direction, the two emitting walls extending on both sides of the predetermined path of the preforms, each emitting wall comprising at least one emitting element for emitting monochromatic or pseudo-monochromatic electromagnetic radiation, the emitting element being arranged to emit radiation towards the preforms passing through the housing, at least one removable wall extending outside the housing in a predetermined area on each emitting wall, the safety system comprising at least two image acquisition devices, each image acquisition device being oriented towards one of the predetermined areas, the processing device being arranged to detect the presence of the removable wall in the image acquired by the image acquisition device;
[0018] - the safety system further comprises an alarm device arranged to warn the operator and / or to stop or prevent the operation of the thermal treatment unit if the treatment device detects the absence of a removable wall in a predetermined area;
[0019] The image acquisition device is movable relative to the housing and / or comprises at least one movable element, so that the image acquisition device acquires images of a plurality of predetermined areas by moving relative to the housing to detect the presence of a removable wall in the plurality of predetermined areas. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The invention will emerge more clearly from a reading of the following description given purely by way of non-limiting example and with reference to the accompanying drawings, in which:
[0021] Figure 1 : Figure 1 is a schematic perspective view of a portion of a heat treatment unit according to the invention, and
[0022] Figure 2: Figure 2 yes Figure 1 Schematic perspective view of a heat treatment unit without the removable walls of the enclosing housing. DETAILED DESCRIPTION
[0023] Reference Figure 1 and Figure 2 A heat treatment unit 1 or a furnace of a container manufacturing plant for manufacturing containers from preforms 2 is described.
[0024] The heat treatment unit comprises two walls 6 ( Figure 2 ) is defined by a housing 4, wherein at least one wall is an emitting wall, and the emitting wall includes at least one emitting element for emitting monochromatic or pseudo-monochromatic electromagnetic radiation. The preform 2 passes along a predetermined passage path T defined in a longitudinal direction in the housing 4. The walls 6 are spaced apart from each other in a transverse direction substantially perpendicular to the longitudinal direction so as to extend on both sides of the passage path T. Figure 1 and Figure 2 , the path T is shown as a straight line, but it should be understood that in some configurations of the container manufacturing device, the path can be curved. Therefore, as a variant, the preform 2 passes along a circular predetermined passage path T in the housing 4. The thermal treatment unit includes a system 8 for clamping and moving the preform 2 along the passage path T between the walls 6. The preforms 2 are more specifically held so that their respective axes extend in an upright direction that is substantially perpendicular to the longitudinal and transverse directions. In other words, the upright direction corresponds to the height of the preform 2 and the height of the wall 6. In a known manner, the clamping system can be arranged so that the preform 2 rotates around its axis when traveling along the path T.
[0025] The emitting element comprises, for example, a plurality of monochromatic or pseudo-monochromatic electromagnetic radiation sources. More specifically, the emitting element is, for example, a laser emitter, the radiation source being a laser chip, which is arranged to emit laser radiation in the infrared range in an emission direction substantially parallel to the transverse direction. The radiation sources are arranged, for example, side by side and one above the other on a support so as to form a row of radiation sources extending in the longitudinal direction.
[0026] Such an emitting element is described, for example, in document FR 3 124 030, to which a person skilled in the art may refer for more details, in particular as to the structure of each radiation source, their arrangement on the support, their connection to one another and the cooling of the heating element.
[0027] The emitting wall 6 comprises, for example, a plurality of emitting elements as described above, which are distributed on the wall 6 at least in the longitudinal direction, or as a variant or as a complement, at least in the vertical direction.
[0028] According to one embodiment, both walls 6 are emitting walls as described above. It should be noted that each wall 6 may also include reflective elements arranged to reflect radiation from the emitting elements of the opposite wall. Such a housing arrangement is described, for example, in document FR 3 124 030, to which a person skilled in the art may refer.
[0029] Therefore, due to the large number of emitting elements and reflections inside the housing, it is understandable that radiation can easily be emitted outside the housing, posing a risk to operators moving around the thermal treatment unit. This problem arises in particular at the inlet and outlet of the housing 4, i.e. at the locations where the preforms 2 enter and leave the housing. In fact, the housing 4 must be open in these areas in order to leave a passage for the preforms 2.
[0030] According to one embodiment, at least one compartment 10 is arranged at the inlet and / or outlet of the housing 4. Figure 2 As shown in , such a compartment 10 is arranged downstream of an opening 12 allowing the preforms 2 to enter the housing 4 and upstream of the emission walls 6, and / or upstream of an opening allowing the preforms 2 to leave the housing 4 and downstream of the emission walls 6, the upstream and downstream being defined according to the direction of passage of the preforms 2 in the housing 4. Such a compartment 10 is arranged to limit, or even eliminate, the radiation that may pass through the opening associated with this compartment 10 by forming a radiation trap inside the compartment. To this end, the compartment 10 is provided, for example, with shields 14 that extend in a predetermined path T of the preforms 2, for example between successive preforms 2, when the preforms 2 pass through the compartment 10, so as to block radiation directed towards the opening 12. These shields are, for example, rotatably movable so as to form a turnstile through which the preforms 2 must pass before passing between the emission walls 6 and / or after passing between these walls 6. Such a compartment 10 is described, for example, in document WO 2011 / 110791, so that they are not described in detail here. A person skilled in the art may refer to this document for more details on the implementation and arrangement of such a compartment 10 in a thermal treatment unit 1 .
[0031] like Figure 1As shown, the housing 4 of the heat treatment unit 1 is also enclosed in a shield 16, which is arranged to prevent the radiation emitted in the housing 4 from leaving the housing 4. Therefore, the shield 16 is arranged to isolate the housing 4 from the place where the heat treatment unit 1 is placed as much as possible, so that operators can pass around the heat treatment unit 1 without risk of exposure to the radiation emitted in the housing 4. Therefore, the shield 16 closes the housing 4 along a predetermined path T at least on both sides of the housing 4 in the transverse direction and at least above the housing 4 in the vertical direction Z. To this end, the shield 16 extends along the walls 6 on the outside of the walls 6, covering the space extending between the walls 6 and the walls 6 above the housing 4. On the lower side of the housing 4, the shield 16 comprises, for example, an opening in the form of a slit to allow the passage of a system 8 for moving and clamping preforms 2 between the inside and the outside of the housing 4. The shield 16 also defines an opening 12 for the preforms 2 to enter and / or leave the housing 4, that is, the opening 12 is made in the shield. When one or more compartments 10 are provided, the shield 16 also surrounds the one or more compartments, such as Figure 1 shown.
[0032] The shield 16 comprises at least one removable wall 18 forming part of the shield 16. By removable wall 18 is meant that the removable wall 18 can be reversibly separated from the shield 16 and the rest of the housing 4, for example in order to release access to the housing 4 and elements extending therein for maintenance operations or other operations. To this end, the removable wall 18 is mounted on the housing of the shield 16, for example by reversible fastening elements, which allow fastening the removable wall 18 to the housing and dismantling the removable wall 18 in order to separate it from the housing. The removable wall 18 extends between an inner surface 20, which faces the interior of the housing 4 when the removable wall 18 is mounted on the housing, and an outer surface 22, which faces opposite the inner surface 20 and faces the exterior of the housing 4. The removable wall 18 is arranged to prevent radiation emitted by the emitting element from passing from the inner surface 20 to the outer surface 22 of the removable wall 18. To this end, the removable wall 18 can be made of a material that prevents this passage, for example absorbs radiation to prevent this passage, or the inner surface 20 can be coated with such a material. As a variant, the material can be a material that reflects radiation. The removable wall 18, for example, complies with a laser passive protector as defined in the CEI 60825-4 (corresponding to the English IEC 60825-4) standard.
[0033] The removable wall 18 is arranged in a predetermined area of the housing 4. The predetermined area corresponds in particular to an area in which radiation emitted by the emitting element in the absence of the removable wall 18 can leave the housing 4, while the radiation is blocked by the housing when the removable wall 18 is mounted on the rest of the shield 16. Thus, the predetermined area extends, for example, at the edge of the opening 12 of the housing, or along a portion of the emitting wall 6 or facing the emitting wall 6. In other words, the removable wall 18, for example, defines at least one edge of the opening 12 of the housing 4 and / or extends in a transverse direction towards one or more emitting elements.
[0034] According to a particularly advantageous embodiment, Figure 1 As shown, the shield 16 is formed by an assembly of multiple removable walls 18, that is, the shield 16 is completely removable. Each removable wall 18 is arranged in a predetermined area of the housing 4, and their assembly allows the housing 4 to be completely closed outside the area where the housing 4 must be opened, as described above. It can therefore be understood that when all removable walls 18 are installed on the housing 4, radiation leakage may only occur at the openings provided in the housing 4, and the housing 4 may be provided with elements for reducing the risk of leakage at the openings, such as the compartment 10 described above. It is also understood that when the thermal treatment unit is in operation, the absence of a removable wall 18 in the corresponding predetermined area may lead to radiation leakage at the predetermined area, thereby causing risks to operators active opposite to the predetermined area or to facilities placed opposite to the predetermined area.
[0035] If the case where the thermal treatment unit 1 comprises a single removable wall 18 is considered, to ensure the presence of this removable wall 18 on the housing 4, the thermal treatment unit according to the invention comprises a safety system comprising at least one image acquisition device 24 arranged to acquire at least one image of at least this predetermined area of the shield 16, towards a predetermined area in which the removable wall 18 should extend. The safety system further comprises processing means 26 for processing the images acquired by the image acquisition means 24, the processing means 26 being arranged to detect the presence of the removable wall 18 in the acquired images of the predetermined area. Thus, the safety system allows, for example, to check that the removable wall 18 is indeed in place before any start-up of the thermal treatment unit 1. According to one embodiment, the safety system further comprises an alarm device arranged to warn the operator and / or to stop or prevent the operation of the thermal treatment unit if the processing means detects the absence of the removable wall 18 in the predetermined area. In this way, it is ensured that the thermal treatment unit is operated only when the removable wall 18 is indeed in place.
[0036] The image acquisition device 24 is preferably arranged outside the housing 4 to acquire an image of the outer surface 22 of the removable wall 18, such as Figure 1 shown.
[0037] The image acquisition device 24 comprises, for example, at least one camera, which captures images in at least the visible light range, the camera being oriented so that at least the predetermined area extends within the range of the camera. According to one embodiment, the camera is also arranged to capture images in the near infrared range, so that the images captured by the camera can show the presence of radiation emitted into a predetermined area outside the housing 4. By near infrared, it is meant that the wavelength is approximately between 0.7 μm and 1.6 μm. Therefore, the processing device for processing the acquired images can allow determining whether there is leakage of radiation outside the housing 4 by analyzing the images captured by the camera. This embodiment is particularly advantageous when the camera is arranged to capture images around the opening 12 for the preform 2 to enter the housing 4 and / or leave the housing 4 (where the risk of leakage is also the greatest). However, this embodiment is still advantageous for other predetermined areas, in particular for detecting whether the removable wall 18 is damaged and allows radiation to pass from the inner surface 20 to the outer surface 22. The alarm device can then be arranged to warn the operator and / or stop or prevent the operation of the thermal treatment unit if the processing device detects the presence of a leak in the predetermined area. By way of example, when the detected radiation level exceeds the maximum permissible exposure value (EMP: corresponding to MPE in English) as defined in the CEI60825-1 (corresponding to IEC 60825-1 in English) standard and / or exceeds the protective exposure limit (LEP: corresponding to PEL in English) as defined in the CEI 60825-4 (corresponding to IEC 60825-4 in English) standard, intervention of the alarm device can be triggered.
[0038] According to one embodiment, when the thermal treatment unit 1 comprises a plurality of removable walls 18, in particular a plurality of removable walls 18 adjacent to one another, the image acquisition device 24 is arranged to acquire one or more images of the plurality of removable walls 18, for example by providing a camera frame to include a plurality of predetermined areas for acquisition, so that the acquisition of a single image by the camera allows the detection of the presence or absence of all these removable walls 18. As a variant or as a supplement, the image acquisition device 24 is movable relative to the housing 4 and / or comprises a movable part, such as a mirror, so that the image acquisition device can acquire some images of the plurality of predetermined areas in order to detect the presence or absence of the removable walls 18 in these predetermined areas. Thus, the image acquisition device 24 is movable, for example, in rotation, in order to scan the plurality of predetermined areas and acquire at least one image for each of these predetermined areas. The processing device 26 is then configured to determine in each image whether a removable wall 18 is present in each predetermined area.
[0039] If it is necessary to obtain an image of each removable wall 18 of the shield 16, the security system may include a plurality of image acquisition devices 24, such as Figure 1 Therefore, by way of example, at least one image acquisition device 24 may be provided for each emitting wall 6. Figure 1In the illustrated embodiment, an image acquisition device 24 is additionally arranged facing the opening 12 , which is particularly advantageous when the acquired images are also used to detect radiation leakage through the opening 12 .
[0040] The image processing device 26 is configured, for example, to compare the acquired image with an image in which all removable walls 18 are present, corresponding to the predetermined area whose image is acquired by the image acquisition device 24. Therefore, once there is a difference between the processed image and the image in which all removable walls 18 are present, the image processing device allows to determine in a simple manner whether the removable wall 18 is not present in the image.
[0041] As a variant or as a supplement, each removable wall 18 may include at least one identification element 28, the image of which is captured by the image acquisition device 24 during the check for the presence of the removable wall 18. The image processing device 26 is then configured to detect the presence of the identification element 28 in the image captured by the image acquisition device 24 in order to determine whether the removable wall 18 is present in the predetermined area. In addition to checking the presence or absence of the removable wall 18, the detection of the identification element 28 may also allow determining whether the detected removable wall 18 is indeed the removable wall that must be placed in the predetermined area whose image has been captured. In fact, the identification element 28 allows each removable wall 18 to be distinguished from the other removable walls and allows a removable wall 18 to be associated with a predetermined area in an individual manner. In addition to the image comparison described above, the detection of the identification element 28 can also be performed, as an alternative to the comparison, so that the positioning of the identification element in the image can be realized in a simpler way than the image comparison, in particular from a software point of view. The identification element 28 is formed, for example, by a QR code, such as Figure 1 As shown, or formed by any other suitable identification element such as a bar code or others. Figure 1 In the embodiment shown, the identification element 28 is applied to the outer surface 22 of the removable wall 18 when the image acquisition device 24 is arranged outside the housing.
[0042] In the figure, each image acquisition device 24 is associated with an image processing device 26. However, it should be understood that the same image processing device 26 can be used for a plurality of image acquisition devices 24. As a variant, the image acquisition device 24 and the image processing device 26 can be combined to form part of the same system, for example in the same housing.
[0043] As previously described, for example, the detection of the presence of the removable walls is triggered before any start-up or restart of the thermal treatment unit 1 , which start-up or restart is prevented as soon as it is determined that at least one removable wall 18 is not in place.
Claims
1. A heat treatment unit (1) for heat treating preforms (2) of a container manufacturing device, the heat treatment unit comprising a housing (4), the preforms (2) travelling along a predetermined path (T) in the housing, the heat treatment unit further comprising at least one emission wall (6), the emission wall comprising at least one emission element for emitting monochromatic or pseudo-monochromatic electromagnetic radiation, the emission element being arranged to emit radiation to the preforms (2) passing through the housing (4), the housing (4) being at least partially enclosed by at least one removable wall (18), the removable wall being arranged to prevent the radiation from passing through the removable wall to the preforms (2) passing through the housing (4). The heat treatment unit is characterized in that the heat treatment unit further comprises at least one safety system, the safety system comprising at least one image acquisition device (24) and at least one processing device (26), the image acquisition device is directed toward the predetermined area and the processing device is used to process the image acquired by the image acquisition device (24), the image acquisition device (24) is arranged to acquire at least one image of the predetermined area, and the processing device (26) is configured to detect whether the removable wall (18) exists in the acquired image.
2. The heat treatment unit according to claim 1, characterized in that The removable wall (18) comprises at least one identification element (28), the image acquisition device (24) is arranged to acquire at least one image of the identification element (28), and the processing device (26) is configured to detect whether the identification element (28) is present in the acquired image.
3. The heat treatment unit according to claim 1 or 2, characterized in that: The image acquisition device (24) comprises at least one camera, which captures images in at least the visible light range, the camera being oriented so that at least the predetermined area extends within the range of the camera.
4. The heat treatment unit according to any one of claims 1 to 3, characterized in that: The housing (4) is at least partially enclosed by a plurality of adjacent removable walls (18), each of which extends in a predetermined area, and the image acquisition device is arranged to acquire at least one image of all the predetermined areas, so that the processing device (26) detects whether all the removable walls (18) exist based on at least one single image acquired by the image acquisition device (24).
5. The heat treatment unit according to any one of claims 1 to 4, characterized in that: The image acquisition device (24) also acquires images in the near infrared range, and the images acquired by the image acquisition device (24) are capable of showing radiation emitted into a predetermined area. The processing device (26) is arranged to identify the presence of radiation leakage outside the housing (4) if at least one image acquired by the image acquisition device (24) shows radiation emitted into the predetermined area.
6. The heat treatment unit according to any one of claims 1 to 5, characterized in that: The heat treatment unit further comprises at least one opening (12) to the housing (4) for passing the preforms (2) into or out of the housing (4), at least one removable wall (18) defining at least a portion of the opening (12).
7. The heat treatment unit according to any one of claims 1 to 6, characterized in that: At least one removable wall (18) extends toward the radiating element in a transverse direction substantially perpendicular to the longitudinal direction.
8. The heat treatment unit according to any one of claims 1 to 7, characterized in that The housing (4) is defined by two emitting walls (6) in a lateral direction substantially perpendicular to the longitudinal direction, the two emitting walls extending on both sides of a predetermined path (T) of the preform (2), each emitting wall (6) comprising at least one emitting element for emitting monochromatic or pseudo-monochromatic electromagnetic radiation, the emitting element being arranged to emit radiation to the preform (2) passing through the housing (4), at least one removable wall (18) extending outside the housing (4) in a predetermined area on each emitting wall (6), the safety system comprising at least two image acquisition devices (24), each image acquisition device being oriented towards one of the predetermined areas, and the processing device (26) being arranged to detect whether the removable wall (18) is present in an image acquired by the image acquisition device (24).
9. The heat treatment unit according to any one of claims 1 to 8, characterized in that: The safety system further comprises an alarm device arranged to warn an operator and / or to stop or prevent operation of the thermal treatment unit if the treatment device detects that a removable wall (18) is not present in a predetermined area.
10. The heat treatment unit according to any one of claims 1 to 9, characterized in that The image acquisition device (24) is movable relative to the housing and / or includes at least one movable element, so that the image acquisition device (24) acquires images of multiple predetermined areas by moving relative to the housing (4) to detect whether the removable wall (18) exists in the multiple predetermined areas.