Measuring chamber for mounting on a smoke detection unit with a light trap based on the principle of a Fresnel lens

Description

[0001] The invention relates to a method for manufacturing a measuring chamber. The invention further relates to a smoke detection module with a smoke detection unit manufactured according to such a manufacturing method. Finally, the invention relates to a smoke detector, in particular a scattered light smoke detector.

[0002] The use of such measuring chambers in smoke detectors is well known. They are also referred to as optical measuring chambers or labyrinths.

[0003] From EP 0 135 361 A2, a light absorber for use in a measuring tube with sensitive optical contamination detectors is known, wherein the light absorber comprises a central light-receiving conical surface surrounded by at least one annular, frustoconical surface to form at least one annular groove or valley surrounding the central zone, wherein a wall of the groove or a wall of the valley shields direct incident light.

[0004] From DE 602 01 208 T2 (translation of European patent EP 1 253 566 B1) an injection molding process for manufacturing the labyrinth wall of a smoke chamber of a fire detector unit of a scattered light detection type is known.

[0005] Smoke detection units integrated into optoelectronic components as a system-on-a-chip (SoC) are known from EP 3 499 475 A2 and EP 3 319 057 A1.

[0006] The smoke detection unit, designed as an SMD component in EP 3 499 475 A2, comprises an infrared LED, a blue LED, and a spectrally matched photodiode. In the assembled state of the smoke detection unit, the optical axes of the LEDs run transversely, i.e., almost orthogonally, to the circuit board. The optical axis of the photodiode also runs orthogonally to the circuit board. Furthermore, a measuring chamber for application on a circuit carrier is described, which incorporates such an integrated smoke detection unit. The measuring chamber is transparent to the smoke to be detected but shielded from direct ambient light.

[0007] The problem here is that, due to the extreme backscattering arrangement of approximately 160°, a significant portion of the light emitted by the two LEDs towards the opposite measuring chamber is scattered and / or reflected back to the photosensor or photodiode as a so-called base pulse. If such a measuring chamber has an assumed diameter of 25 mm and a height of 15 mm, the received light intensity level of the reflected base pulse exceeds the alarm level for fire detection many times over. Reliable smoke detection is therefore impossible.

[0008] A further reduction of the basic pulse is possible, for example, by means of a cone known from US 2009 / 237259 A1, which is formed on the inside of the measuring chamber and deflects the incident light cone laterally.

[0009] Starting from this, one object of the present invention is to provide a manufacturing method for a measuring chamber in which the influence of the basic pulse is reduced.

[0010] Finally, it is an object of the invention to provide a smoke detection module with such a measuring chamber, manufactured according to the inventive method, and a smoke detector with such an inventive smoke detection module.

[0011] These problems are solved by the features of claim 1. Finally, the problem is solved by a smoke detection module with a measuring chamber produced according to the inventive method and by a smoke detector with such a smoke detection module according to the invention.

[0012] The angular, preferably sharp-edged light trap structures are shaped in such a way that they follow the design-reduced principle of a Fresnel step lens.

[0013] In other words, these light-absorbing structures are a simplified form of a single light trap funnel, analogous to the principle of a Fresnel lens. Furthermore, the light trap structures are shaped in such a way that they are optically aligned to, or approximately aligned with, a common point. When the measuring chamber is properly attached to a designated smoke detection unit, this point ideally lies at the light emitter or light exit point of this smoke detection unit.

[0014] Alternatively, the light-trap structures can be shaped such that they are optically aligned on, or approximately aligned with, a straight line that ideally runs through the transmitting axis directly at the light emitter and preferably through the receiving axis directly at the photosensor. These light-trap structures can also be called Fresnel light-trap structures. They are linear, preferably circular, elliptical, or straight light-trap structures.

[0015] The "optical alignment" of the Fresnel light trap structures means that the bisector of the opening angle of each light trap structure passes through the common point as the "focal point" or intersects the aforementioned line. The bisector runs perpendicular to the tangent that runs along the longitudinal extent of the respective light trap structure, either along its inner edge or along its vertex.

[0016] The core of the invention lies in miniaturizing the design of an "ideal" light trap funnel into a multitude of smaller light trap funnel structures analogous to the Fresnel principle. By aligning these Fresnel light trap structures, the backscatter cross-section as seen from the light emitter is advantageously reduced compared to straight, regularly jagged light-absorbing structures. The fundamental pulse is significantly reduced.

[0017] In a non-inventive embodiment, the (Fresnel) light trap structures have a Fresnel axis, analogous to the focal point of a Fresnel lens. They are also aligned to a common Fresnel point. The Fresnel point lies in a floor plane of the measuring chamber opposite the measuring chamber ceiling, or at a small distance from it, i.e., at a small distance of a maximum of 5 mm, preferably a maximum of 2 mm. The floor plane is the plane defined by an edge of the measuring chamber, resembling a "pot rim." The measuring chamber is designed such that, after the measuring chamber is mounted on or attached to the intended smoke detection unit, this edge lies flat against a circuit carrier of the smoke detection unit or against a flat cover on the circuit carrier. The floor plane thus runs parallel to the plane of the circuit carrier.

[0018] According to another non-inventive embodiment, the Fresnel light trap structures are oriented such that, after the measuring chamber is mounted on a provided smoke detection unit, the Fresnel point is located at the light output of a light emitter of the smoke detection unit. In other words, it is not absolutely necessary for the axis of rotation or axis of rotational symmetry of a typical measuring chamber to coincide with the Fresnel axis.

[0019] Alternatively, the Fresnel light trap structures can be designed or shaped such that, after the measuring chamber is mounted on a designated smoke detection unit, they are optically aligned along a straight line. This straight line runs at least approximately through an optical transmission axis at the light emission point of a light emitter of the smoke detection unit and preferably at least approximately through a receiving axis of a photosensor of the smoke detection unit. This straight line lies in a floor plane of the measuring chamber opposite the ceiling or at a small distance from the floor plane towards the ceiling.

[0020] As a result, the Fresnel light-trap structures are not concentric to the Fresnel axis, but rather linear and thus parallel to it. Compared to the known straight, regularly spaced, jagged light-absorbing structures, this configuration of Fresnel light-trap structures also exhibits a significantly reduced backscatter cross-section. This results in a considerably reduced fundamental pulse.

[0021] A further advantage lies in the fact that these straight Fresnel structures of such a measuring chamber ceiling can also feature undercuts. Such structures cannot be manufactured using a conventional injection molding process with a die and punch—apart from a complex 3D plastic printing process—but can be produced using an extrusion process. In this process, an extruded profile, preferably made of a (black) plastic, with the straight, linear Fresnel structures is first produced using an extrusion process. The measuring chamber ceiling is then cut from this extruded profile, for example, using a stamping process. Finally, the measuring chamber ceiling is assembled together with a complementary, essentially hollow or hollow cylindrical smoke inlet section or a labyrinth section to form the complete measuring chamber.

[0022] In particular, the Fresnel light trap structures are formed by a plurality, such as in the range of 10 to 100, especially in a range of 25 to 50, of notches or grooves arranged concentrically to the Fresnel axis, or by a (single) notch or groove running spirally to the Fresnel axis in the sense of a record.

[0023] Preferably, the measuring chamber ceiling has a measuring chamber ceiling plane that runs parallel to the floor plane of the measuring chamber. The concentrically arranged notches or grooves, or the spirally extending notch or groove, have a respective inner edge and a respective outer edge projecting away from the measuring chamber ceiling. Each outer edge is radially offset outwards relative to a radially inwardly adjacent inner edge such that a flank formed between the two edges runs orthogonally to the measuring chamber ceiling plane.

[0024] An "ideal" Fresnel light trap typically features undercuts in its radial outer region. Therefore, injection molding for the production of such Fresnel light trap structures is technically unfeasible—apart from a complex 3D plastic printing process. By offsetting the inner edges radially outward, it is now advantageously possible to produce a concentric "Fresnel light trap" using an injection molding process. While this solution is not as optically superior to the previous solution with undercut Fresnel light trap structures, it is nevertheless considerably better than the known straight, regularly serrated structures.

[0025] In a non-inventive embodiment, the measuring chamber has a rotation axis or axis of rotational symmetry that runs orthogonally to the ground plane. The Fresnel light trap structures are oriented such that the Fresnel axis runs parallel to, preferably at least approximately aligned with, the rotation axis or axis of rotational symmetry of the measuring chamber. Due to the central arrangement of the light emitter and the adjacent photosensor, the smoke detection unit advantageously exhibits a response to smoke that is largely independent of the direction in the radial direction relative to the Fresnel axis.

[0026] According to another, alternative, non-inventive embodiment, the Fresnel light trap structures are aligned such that the Fresnel axis is at least approximately aligned with an optical transmission axis of the light emitter of the smoke detection unit. This embodiment is advantageous if—as, for example, in the smoke detection unit described above according to EP 3 499 475 A2—the optical transmission axis of the light emitter is not orthogonal to the circuit carrier, but oblique to it, and thus also obliquely passes through the ceiling of the measuring chamber. This "oblique" arrangement of the concentric Fresnel light trap structures around the Fresnel axis advantageously allows for a symmetrical alignment of the Fresnel light trap structures with the obliquely emitted light cone of the light emitter.

[0027] According to a further embodiment not in accordance with the invention, the measuring chamber is particularly cylindrical. The measuring chamber ceiling follows a cylindrical base.

[0028] In a further non-inventive embodiment, the measuring chamber has louvers that are permeable to smoke and shield against direct ambient light. The louvers extend along the circumference of the measuring chamber.

[0029] Preferably, the measuring chamber has an inner diameter in the range of 25 mm to 80 mm, particularly in the range of 25 mm to 50 mm. Alternatively or additionally, it has a measuring chamber height in the range of 10 mm to 40 mm, particularly in the range of 15 mm to 25 mm.

[0030] According to another embodiment not in accordance with the invention, the Fresnel light trap structures have a structural depth in the range of 1 mm to 10 mm, particularly in the range of 1.5 mm to 5 mm, and preferably in the range of 2 mm to 3 mm. "Structural depth" refers to the axial dimensions of the light-absorbing, angular, preferably sharp-edged structures with respect to the Fresnel axis. Preferably, the measuring chamber ceiling of the measuring chamber has a uniform measuring chamber thickness that is greater than the structural depth in the range of 1 mm to 3 mm.

[0031] The object of the present invention is achieved by a method for manufacturing a preferably cylindrical measuring chamber for a smoke detection unit of a smoke detector. First, a measuring chamber ceiling is produced and this is then assembled together with a complementary, substantially hollow or hollow cylindrical smoke inlet part to form the complete measuring chamber.

[0032] The measuring chamber ceiling is manufactured as a spherical component with integrated angular, preferably sharp-edged, concentric light-trap structures using an injection molding process, particularly a plastic injection molding process. These light-trap structures are shaped to function as Fresnel light-trap structures, following the simplified principle of a Fresnel lens. Typically, the Fresnel light-trap structures are aligned with a distant Fresnel point on a Fresnel axis of the measuring chamber ceiling. "Distance" in this context means that this distant Fresnel point is at least 30 mm from the measuring chamber ceiling.

[0033] After the injection molding process, the Fresnel light trap structures of the spherical measuring chamber ceiling are free of undercuts. The spherical measuring chamber ceiling is then formed into a substantially flat measuring chamber ceiling using a forming process. During this process, the Fresnel light trap structures are shaped in the direction of the Fresnel axis. The Fresnel light trap structures now form undercuts. Typically, the most distant Fresnel point on the Fresnel axis also shifts towards a Fresnel point in the floor plane of the measuring chamber or at a small distance therefrom. Thus, after the entire measuring chamber has been manufactured and attached to a designated smoke detection unit, the Fresnel point is located at least approximately at the light output of a light emitter of the smoke detection unit.After the measuring chamber is attached to the intended smoke detection unit, the Fresnel point is located in the same plane as the bottom of the measuring chamber or at a small distance from it. "Small distance" means a maximum distance of 5 mm, preferably a maximum of 2 mm.

[0034] The geometric design of the Fresnel light trap structures in a spherical measuring chamber ceiling can be determined, for example, using a finite element method, so that after the transformation process, the ideal Fresnel light trap structure with the desired undercuts results. For example, a measuring chamber ceiling with "ideal" Fresnel light trap structures with undercuts for the intended measuring chamber can be "transformed" onto a spherical surface with decreasing radius until the measuring chamber ceiling is free of undercuts from a reduced radius onwards.

[0035] According to one embodiment of the manufacturing process according to the invention, the forming process is a blow molding process.

[0036] The object of the invention is further achieved with a smoke detection module. Such a smoke detection module comprises a smoke detection unit with at least one light emitter arranged on a circuit carrier and with at least one spectrally tuned photosensor, each in a scattering light arrangement. The at least one light emitter and the at least one spectrally tuned photosensor are located directly opposite the ceiling of the measuring chamber. The scattering angle between the respective optical transmit and receive axes of the at least one light emitter and the at least one photosensor of the smoke detection unit is, in particular, in the range of 160° to 185°. Such a scattering light arrangement is also referred to as a backscattering light arrangement.

[0037] The at least one light emitter and the at least one spectrally tuned photosensor can also be an already integrated optoelectronic unit, i.e. a so-called system-on-a-chip (SoC), in particular a system-on-a-chip designed as an SMD component.

[0038] Furthermore, the smoke detection module comprises a measuring chamber manufactured according to the previously described manufacturing process of the invention. The measuring chamber is mounted on or above the smoke detection unit. Together with the circuit carrier, on which a bottom rim or a "pot rim" of the measuring chamber rests, the measuring chamber encloses the at least one light emitter and the at least one photosensor. The circuit carrier can also have a flat plastic cover, preferably with apertures for the at least one light emitter and / or photosensor, with a spatial recess for the at least one light emitter and / or photosensor.

[0039] According to one embodiment, the measuring chamber has an axis of rotation or an axis of rotational symmetry, wherein the measuring chamber is positioned on the circuit carrier such that the axis of rotation or the axis of rotational symmetry of the measuring chamber, or the Fresnel axis of the Fresnel light trap structures, is at least approximately aligned with an optical transmission axis of the light emitter of the smoke detection unit. Due to the central arrangement of the at least one light emitter and the adjacent at least one photosensor, the smoke detection module advantageously exhibits a response behavior to smoke that is largely independent of the direction in the radial direction relative to the Fresnel axis.

[0040] In general, "at least approximately" in relation to the alignment of the Fresnel axis or axis of rotation or rotational symmetry to the light emitter or to the light exit point of the light emitter means a permissible deviation of a few millimeters, in particular of less than 5 mm.

[0041] When reference is generally made to the alignment with a light emitter or the light emission point of a light emitter, in the case of two existing light emitters, this refers to an alignment with one of the two light emitters or with the light emission point of one of the two light emitters, or an alignment with a geometrically located point between the two light emitters or between the two light emission points between the two light emitters.

[0042] In a particular embodiment, an aperture is optically connected downstream of the at least one light emitter to limit the respective emitted light cone. A further aperture is optically connected upstream of the at least one photosensor to limit the respective optical detection area. The optical limits are dimensioned such that only a fraction of the area of ​​the measuring chamber ceiling illuminated by the respective light emitter lies within the optical detection range of the at least one photosensor, typically between 10% and 40%, preferably between 10% and 20%. This advantageously reduces the influence of the illuminated area on the fundamental signal.

[0043] The problem is solved by a smoke detector, in particular by a scattered light smoke detector, which comprises a detector housing and a smoke detection module according to the invention housed within the detector housing. The detector housing has one or more smoke inlet openings for the passage of ambient air into the interior of the detector housing and further into the measuring chamber of the smoke detection module.

[0044] Finally, the problem is solved by a further smoke detector, in particular a scattered light smoke detector, which comprises a detector housing and a smoke detection module according to the invention housed within the detector housing. The measuring chamber of the smoke detection module is an integral part of the detector housing. The detector housing has one or more smoke inlet openings designed as louvers, which are permeable to smoke to be detected and shield against direct ambient light.

[0045] The smoke detectors or scattered light smoke detectors under consideration are either smoke gas detectors or smoke alarms. They may also include a gas sensor for detecting fire-related gases and / or a temperature sensor. Furthermore, these smoke detectors may be connected to a fire alarm control panel via a common detector line or circuit, particularly a two-wire line, for signal and / or data transmission. Alternatively or additionally, they may have an independent power supply, such as a battery. These smoke detectors may also include a radio module for transmitting an alarm, warning, or status message to a neighboring smoke detector or to a fire alarm control panel.

[0046] The invention and advantageous embodiments of the present invention are evident from the following figures. FIG 1 a sectional view through a smoke detection module according to the prior art, FIG 2 a top view of the smoke detection module according to FIG 1 FIG. 3 the principle of size reduction in an optical Fresnel lens, FIG. 4 the transfer of the principle according to FIG 3 on a light trap funnel, FIG. 5 a section through an exemplary measuring chamber with known straight, uniformly serrated light-absorbing structures and with Fresnel light trap structures according to the invention in a common representation, FIG. 6 a view of the measuring chamber ceiling according to the one shown in FIG 5 The indicated viewing direction VI shows the known straight, evenly jagged structures and concentric Fresnel light trap structures with undercuts, FIG. 7 a view of the measuring chamber ceiling according to the one shown in FIG 5 FIG. 8 shows a section through an exemplary measuring chamber with the concentric Fresnel light trap structures with undercuts and with further concentric Fresnel light trap structures without undercuts, each according to the invention, FIG. 9 shows a section through a scattered light smoke detector with a detector housing and with a smoke detection module included therein according to the invention, FIG. 10 shows an exemplary injection molding process as a first stage of a manufacturing process for a measuring chamber ceiling for a measuring chamber according to the invention, FIG. 11 shows an exemplary forming process as a second stage of the manufacturing process for the measuring chamber ceiling for a measuring chamber according to the invention, and FIG. 12 shows an exemplary joining process as a third stage of the manufacturing process for the entire measuring chamber according to the invention.

[0047] FIG 1 Figure 1 shows a cross-sectional view through a smoke detection module 1 according to the state of the art. M denotes a trough-shaped or pot-shaped measuring chamber, which is enclosed by a circuit carrier 4. LA denotes radially outward-facing louvers, extending around an axis of rotation or rotational symmetry A of the measuring chamber M, which shield the interior of the measuring chamber M from direct ambient light. An optoelectronic surface-mount device (SMD) component, SoC, is integrated as a system-on-a-chip (SoC). This SoC comprises a light-emitting diode (LED) as a light emitter 2 and a photodiode as a photosensor 3. A microcontroller (MC) is connected to this SoC. The MC is configured to control the LED to emit light pulses and to receive and evaluate a sensor signal from the photosensor 3, and, if necessary, to issue a fire alarm AL.

[0048] LK denotes the light cone emitted by the light-emitting diode 2, and SA denotes the corresponding optical transmission axis. FOV denotes the optical detection area of ​​the photosensor 3. In this example, the optical reception axis of the photosensor 3 is aligned with the symmetry axis A of the measuring chamber M. The transmission axis SA is slightly inclined relative to the optical reception axis, resulting in a larger scattered light volume SV as the geometric intersection of the light cone LK and the optical detection area FOV. α denotes the scattering angle between the optical transmission and reception axes SA, A. Here, it is approximately 160°. Such a scattered light arrangement is also referred to as a backscattered light arrangement.

[0049] In contrast to other known scattering arrangements, where the optical axes SA and EA of the light emitter 2 and photosensor 3 run parallel to the plane of the circuit carrier 4, here the measuring chamber ceiling D is, so to speak, "fully" illuminated. To suppress the directly incident light from the light emitter 2 as much as possible, the inner surface of the measuring chamber ceiling D, directly opposite the light emitter 2 and the photosensor 3, features light-absorbing structures AB in the form of small, jagged light traps. However, with this arrangement, a portion of the light emitted by the light emitter 2 is scattered back towards the photosensor 3, the light level of which is many times higher than the alarm level triggered by an impermissibly high concentration of smoke in the measuring chamber M. Reliable smoke detection is therefore impossible.

[0050] FIG 2 shows a top view of the smoke detection module 1 according to FIG 1 . In this illustration, the structure of the integrated SoC unit with the LED 2 and the photodiode 3 as well as the lamellae LA for shielding against ambient light are clearly visible.

[0051] FIG 3 This illustrates the well-known principle of size reduction in an optical Fresnel lens (FLI). In the left part of the FIG 3 A plano-convex optical lens LI with its focal point BP is shown. The stepped reduction in design is indicated by a dashed line. In the right part of the FIG 3 The compact Fresnel lens FLI can be seen.

[0052] FIG 4 demonstrates the transfer of the principle according to FIG 3 onto a light trap cone TR. According to the image plane shown, incident light rays from a light emitter 2, i.e., from bottom to top or from bottom to obliquely above, would "dissipate" here after a multitude of reflections. TS denotes a cone tip that is directed at a focal point BP corresponding to the optical Fresnel lens FLI. The angle β denotes the opening angle of the light trap cone TR. The reference symbol R denotes a rounded shape that the light trap cone TR can have as an alternative to the cone tip TS. Such a shape is also well suited as a light trap. The orientation of the light trap cone TR is shown, by way of example, along the axis of symmetry A of the light trap cone TR. T11 denotes the depth of the light trap cone TR. In the following FIG 5 It is shown how the light trap funnel TR would initially be placed as an "ideal" light trap in place of the measuring chamber ceiling D.

[0053] To achieve concentric Fresnel light trap structures FS, a cone serves as the starting point, acting as a light trap funnel TR. To achieve linear, straight Fresnel light trap structures FS, a "saddle roof" serves as the starting point.

[0054] In the FIG 4 The figure shows how the light trap funnel TR is first divided into two adjacent, identical sub-funnels TR-2. The structural depth T12 of the two sub-funnels TR-2 has been halved in the process.

[0055] The left part of the FIG 4 Figure 1 shows how the funnel tip of the left sub-funnel TR-2 is offset radially outwards with respect to the axis of symmetry A, so that the funnel tip of the current partial Fresnel light trap LF-2, and thus its inner edge IK, is optically aligned with the "focal point" BP of the light trap funnel TR. Q denotes the cross-section of the light trap as seen from the "focal point". W denotes the angle bisector of the opening angle β of the partial Fresnel light trap LF-2, which, for illustrative purposes, is shown here perpendicular to the tangent labeled TAN. In reality, the tangent TAN runs perpendicular to the plane of the sheet of the FIG 4 and lies at the inner edge IK of the partial Fresnel light trap LF-2.

[0056] The right part of the FIG 4 This shows a further halving, resulting in a total of four partial funnels TR-4. Their depth T14 is only a quarter of the depth T11 of the original light trap funnel TR. The funnel tips of the two rightmost partial funnels TR-4 are now offset radially outwards with respect to the axis of symmetry A, so that the funnel tips of the current partial Fresnel light traps LF-4, and thus their inner edge IK, are again optically aligned with the "focal point" BP of the light trap funnel TR. In the example shown, FIG 4 The halving was performed uniformly and is merely an example. Dividing the original light trap cone TR into thirds or any other type of division is also possible. The respective structural depths T12 and T14 can also differ. The crucial point is that a number of arbitrary sub-cones, also with arbitrary structural depths, are arranged side by side, optically aligned with the "focal point." The arrangement shown, with the optical alignment along the respective angle bisectors to the "focal point," is particularly effective as a light trap.

[0057] FIG 5 Figure 1 shows a cross-section through an exemplary measuring chamber M with known straight, uniformly jagged light-absorbing structures AB and with Fresnel light-trap structures FL, FLM in a combined representation. It shows how the "ideal," but space-consuming, light-trap funnel TR would be placed as the "ideal" light trap instead of the measuring chamber ceiling D shown.

[0058] MH denotes the overall height of the measuring chamber M, and T represents, for example, the uniform structural depth of the light-absorbing structures AB and the Fresnel light-trap structures FL and FLM. DD denotes the diameter of the measuring chamber ceiling D, and DLF the diameter of the Fresnel light-trap structures FL and FLM shown.

[0059] In the left part of the FIG 5 Known triangular, jagged light-trap structures AB can be seen. The further radially they are located from the axis of symmetry A, the less these structures are directed towards the light source 2. The backscattering cross-section increases steadily, which is detrimental.

[0060] In the right part of the FIG 5 Starting from the triangular light trap structure AB, it can be seen how the inner edges IK of the respective light trap structures are optically aligned with a Fresnel point FP on the light emitters 2 by means of the radial outward displacement – ​​symbolized by directional arrows. Furthermore, the Fresnel point FP is located at a distance AF from the floor plane BO at the light emission point of the light emitter 2. The floor plane BO of the measuring chamber M shown runs parallel to a measuring chamber ceiling plane DE at a distance equal to the total height MH of the measuring chamber.

[0061] FIG 6 a view of the measuring chamber ceiling D according to the in FIG 5 The indicated viewing direction VI shows the familiar straight, evenly jagged structures AB in the left part of the FIG 6 and in comparison with concentric Fresnel light trap structures FLM with undercuts UC in the right part of the FIG 6 The undercuts UC themselves are shown with dashed lines. These are hidden along the viewing direction VI and thus also from the perspective of the light emitter 2, and are therefore not visible. As described at the beginning, such a measuring chamber ceiling D with such undercuts UC cannot be manufactured using a conventional injection molding process.

[0062] FIG 7 shows a view of the measuring chamber ceiling D according to the in FIG 5 indicated view direction VII with the familiar structures AB in the left part of the FIG 7 and with now linear, straight Fresnel light trap structures FLM with undercuts UC. A measuring chamber ceiling D with such Fresnel light trap structures FLM can be manufactured using an extrusion process.

[0063] FIG 8 Figure 1 shows a cross-section through an exemplary measuring chamber M with the concentric Fresnel light trap structures FLM with undercuts UC and with further concentric Fresnel light trap structures FLO without undercuts, each according to the invention. This example shows how the Fresnel light trap structures FLM with undercuts UC are modified by radially outward displacement of the outer edges AK in the left part of the FIG 8 now in Fresnel light trap structures FLO without undercuts in the right part of the FIG 8 be transferred.

[0064] FIG 9 Figure 1 shows a section through a scattered light smoke detector 10 designed as a smoke detector. The scattered light smoke detector 10 comprises a detector housing G and a smoke detection module 1 according to the invention received in the detector housing G.

[0065] In a case not shown further, the measuring chamber M according to the invention can be mounted as a separate part within the detector housing G on or above the smoke detection unit 1 of the smoke detection module 1. In this case, the smoke to be detected enters through one or more smoke inlet openings OF present or formed in the detector housing G and further through the louvers LA of the measuring chamber M to the smoke detection unit 1 inside the measuring chamber M.

[0066] In the case shown, the measuring chamber M of the smoke detection module 1 is an integral part of the detector housing G itself. The detector housing G has one or more smoke inlet openings OF designed as louvers LA, which are permeable to smoke to be detected and shield against direct ambient light. For better understanding of the invention, the measuring chamber M shown is analogous to the illustration in FIG 8 The concentric Fresnel light trap structures FLM with undercuts UC and the concentric Fresnel light trap structures FLO without undercuts are shown in a single representation. The detector housing G can also include further housing parts, such as a detector cover H or a receptacle AUF for at least detachably attaching the smoke detector 10 to a detector base MS. The detector housing G can be composed of a base body GK and the detector cover H. The measuring chamber M according to the invention is preferably integrally formed or molded between these components as part of the detector housing G. The part of the circuit carrier 4 of the smoke detection module 1 or of the smoke detector 10 itself, opposite the measuring chamber ceiling D, can be covered with additional light-absorbing structures AB.

[0067] HA denotes a main axis of the preferably substantially symmetrical or rotationally symmetrical detector housing G. In particular, this main axis HA, the Fresnel axis FA of the measuring chamber M, and preferably the transmitting axis SA of the light emitter 2 of the smoke detection unit are aligned with each other. This results in a largely direction-independent response of the smoke detector 10 to smoke to be detected.

[0068] FIG 10 Figure 1 shows an exemplary injection molding process as the first stage of a manufacturing process for a measuring chamber cover D for a measuring chamber M according to the invention. In the upper part of the FIG 10 A stamping tool STP and a die MAT are visible in the lower part. Between them, the spherical measuring chamber cover D, produced after the first stage, can be seen as an intermediate product. Due to the linear injection molding process used, the latter exhibits Fresnel light trap structures FLO without undercuts.

[0069] FIG 11 Figure 1 shows an exemplary forming process as the second stage of the manufacturing process for the measuring chamber ceiling D for a measuring chamber according to the invention. BLA denotes a blow mold by means of which the spherical measuring chamber ceiling D contained therein is formed, for example, by injecting air, from its spherical shape into its final flat shape. Venting channels are shown as dashed lines in the blow mold BLA. This illustration also shows how a distant Fresnel point EFP is displaced along the Fresnel axis FA towards the measuring chamber ceiling D by the forming process. After the forming process, the now flat measuring chamber ceiling D exhibits Fresnel light trap structures FLM with undercuts UC.

[0070] FIG 12 Figure 1 shows an exemplary joining process as the third stage of the manufacturing process for the entire measuring chamber M according to the invention. MO denotes the smoke inlet part of the measuring chamber M, into which the measuring chamber ceiling D is inserted. FIG 11 The components are inserted using a joining process and then assembled into the complete measuring chamber M according to the invention. The joining can be carried out, for example, by gluing, ultrasonic welding, using a snap-fit ​​pin, or similar methods. Reference symbol list

[0071] 1 Smoke detection module 2 Light emitter, LED 3 Photosensor, photodiode 4 Circuit carrier, printed circuit board 10 Fire alarm, smoke detector α Scattering angle β Opening angle A Axis of symmetry, rotational symmetry A Light-absorbing structures, light trap structures A Floor distance, distance of the Fresnel point A Outer edges of the light trap structure A Fire alarm A Recording B B Stretch blow tool, blow tool B Measuring chamber floor, plane of the measuring chamber floor B Focal point D Measuring chamber ceiling D Diameter of the measuring chamber ceiling D Measuring chamber ceiling plane DLF Diameter of the Fresnel light trap structure E Optical receiving axis E F Distant Fresnel point F A Fresnel axis FL Fresnel light trap structure FL-2, FL-4 Partial Fresnel light traps F I Fresnel lens F L M Fresnel light trap with undercuts F L Fresnel light trap without undercuts F O Optical Detection area,Field-of-View (FFP) Fresnel point GM Detector housing GK Base body HM Detector hood HA Vertical axis IK Internal edges of the light trap structure LA Louvers, labyrinth LI Optical lens, plano-convex lens LK Light cone, light beam M Measuring chamber, measuring chamber with labyrinth MAT Matrix MC Control unit, microcontroller MH Measuring chamber height MO Measuring chamber without inserted measuring chamber ceiling, smoke inlet section, labyrinth section MS Detector base OF Smoke inlet opening Q Light trap cross-section R Curvature, radius SA Optical transmission axis SoC System-on-a-Chip, integrated unit STPS Stamping tool SV Measuring volume, scattering volume T Depth of the Fresnel light trap structure T11 Depth of the light trap funnel T12, T14 Depth of a sub-funnel TANTangent TR Light trap funnel, funnel TR-2, TR-4 Sub-funnel TST Funnel tip UCU Undercut, undercut W Angle bisector

Claims

1. Method for producing a preferably cylindrical measurement chamber (M) for a smoke detection unit of a smoke detector (10), wherein at first a measurement chamber cover (D) is created and this is combined with a complementary, essentially hollow or hollow cylindrical smoke inlet part (MO), to make up the measurement chamber (M) as a whole, wherein the measurement chamber cover (D) is produced by means of an injection moulding process (STP, MAT) as a spherical component (FLO) with introduced angular, preferably sharp-edged concentric light trap structures, which are shaped in such a way that they are Fresnel light trap structures (FL) following the compact-design principle of a Fresnel stepped lens (FLI), wherein in this context the design of an ideal light trap funnel is reduced into a large number of smaller light trap funnel structures analogous to the Fresnel principle, wherein the Fresnel light trap structures (FL) of the spherical measurement chamber cover (FLO), after the injection moulding process (STP, MAT), are free of undercuts (UC), and wherein the spherical measurement chamber cover (FLO) by means of a deformation process (BLA), in particular by means of a blow moulding process, is formed into an essentially flat measurement chamber cover (FLM), wherein the Fresnel light trap structures (FL) are shaped in the direction of the Fresnel axis (A) and form now undercuts (UC), wherein the Fresnel point (FP), after the measurement chamber (M) as a whole has been produced and after it has been attached to a smoke detection unit provided, is preferably located at the light exit of a light emitter (2) of the smoke detection unit.

2. Smoke detection module (1), with a smoke detection unit comprising at least one light emitter (2) arranged on a circuit carrier (4) and at least one spectrally matched photosensor (3) in a scattered light arrangement in each case, and with a measurement chamber (M) produced according to a method according to claim 1, wherein the measurement chamber (M) is attached to the smoke detection unit.

3. Smoke detection module according to claim 2, wherein the measurement chamber (M) has an axis of rotation (A) or a rotational symmetry axis (A), wherein the measurement chamber (M) is positioned on the circuit carrier (4) such that the rotational or rotational symmetry axis (A) of the measurement chamber (M), or the Fresnel axis (FA) of the Fresnel light trap structures (FL) is at least approximately aligned with an optical transmission axis (SA) of the light emitter (2) of the smoke detection unit.

4. Smoke detection module according to claim 2 or 3, wherein a diaphragm to limit the respective emitted light beam (LK) is located optically downstream of the at least one light emitter (2), wherein a further diaphragm to limit the respective optical reception area (FOV) is connected optically upstream of the at least one photosensor (3), and wherein the optical limits are dimensioned in such a way that only a proportion of the area of the part of the measurement chamber cover (D) illuminated by the respective light emitter (2) is in a range of 10% to 40%, preferably in a range of 10 to 20%, in the respective optical detection range (FOV) of the at least one photosensor (3).

5. Smoke detector, in particular a scattered light smoke detector, with a detector housing (G) and with a smoke detection module (1) according to claim 2, 3 or 4 accommodated in the detector housing (G), wherein the detector housing (G) has one or more smoke inlet openings (OF) for the passage of ambient air into the interior of the detector housing (G) and further into the measurement chamber (M) of the smoke detection module (1).

6. Smoke detector, in particular a scattered light smoke detector, with a detector housing (G) and with a smoke detection module (1) according to claim 2, 3 or 4 accommodated in the detector housing (G), wherein the measurement chamber (M) of the smoke detection module (1) is an integral part of the detector housing (G) and wherein the detector housing (G) has one or more smoke inlet openings (OF) embodied as lamellae (LA), permeable to smoke to be detected and shielding from direct ambient light.