Optical prism and particle detection unit with optical prism

Abstract

The invention relates to a particle detection unit (300) having: a first optical prism (101); a second optical prism (102); a housing (200) delimiting a detection chamber (230), which is provided therein and is shielded from ambient light, and having a first prism seat (241) and a second prism seat (242), wherein the prisms (101, 102) are each arranged in a prism seat (241, 242) and are aligned with each other; a printed circuit board (310); a light emitter (320) for emitting light beams in an emission direction; and a light receiver (330) for receiving light beams incident on an area of incidence of the light receiver (330). The aim of the present invention is to provide a compact particle detection unit (300) which allows simple and precise alignment of the optical components relative to one another. This is achieved in that the light emitter (320) and the light receiver (330) are positioned on the same printed circuit board (310) to interact with the first prism seat (241) and the second prism seat (242), respectively, so that light beams emitted from the light emitter (320) in the emission direction pass through a first prism surface (110) of the first prism (101) aligned by the first prism seat (241) and are incident on an internal reflective surface (130) of the first prism, and the area of incidence of the light receiver (330) is aligned with the internal reflective surface (130) of the second prism, passing through a first prism surface (110) of the second prism (102) aligned by the second prism seat (242).

Description

[0001] Optical prism and particle detection unit with optical prism

[0002] The invention relates to an optical prism for a particle detection unit. The prism comprises a first prism surface and a second prism surface, through which light rays can enter or exit the interior of the optical prism, as well as an internal reflection surface that reflects light rays passing through the interior of the optical prism and incident thereon. The invention also relates to a housing for a particle detection unit. The housing comprises an upper shell and a lower shell that can be connected to one another to define a detection chamber arranged within the housing and shielded from ambient light.

[0003] The invention further relates to a particle detection unit comprising a first optical prism and a second optical prism, a housing defining a detection chamber arranged therein and shielded from ambient light, and a first prism seat and a second prism seat, wherein the prisms are each arranged within a prism seat and aligned with one another. The particle detection unit further comprises a circuit board and a light transmitter for emitting light beams in an emission direction, as well as a light receiver for receiving light beams incident in an incidence region of the light receiver.

[0004] Particle detection units are often used for fire detection, particularly in buildings, vehicles, on ships, etc., whereby particles contained in the ambient air of a monitored area, e.g. smoke particles or aerosols, which indicate a fire or its origin, are detected by the particle detection unit. A monitored area is usually an area to be monitored in which people are present, (valuable) goods are stored and / or there is an increased fire risk. Monitoring areas can be parts of a building, such as rooms, storage rooms or server rooms; parts of a vehicle, e.g. a ship, train, bus or aircraft, such as passenger compartments or engine rooms; but also an area in the immediate vicinity or within an object, such as a machine or a control cabinet.

[0005] To detect particles, the detection chamber, which is in fluid communication with the ambient air, is located inside the housing of the particle detection unit. The actual detection range, within which particles transported into the detection chamber with the ambient air can be detected, is usually defined by the superposition of the light beams from the light transmitter and the incidence range of the light receiver within the detection chamber. During detection, the particles are illuminated by the light emitted by the light transmitter and can be detected by the light receiver either based on the transmitted light reduced by the particles (transmitted light detector) or based on the scattered light scattered by the particles (scattered light detector). To ensure that only the light emitted by the light transmitter reaches the particles in the detection range, the detection chamber is shielded from ambient light.

[0006] A well-known application for the use of particle detection units is aspirating smoke detectors, also known as aspirating particle detection systems.

[0007] An intake particle detection system comprises at least one pipe and / or hose line, which opens into one or more monitoring areas via one or more intake openings for the respective extraction of a fluid, in particular an air, sample. Multiple monitoring areas can be arranged, for example, in different areas of the same space, such as a (large) warehouse, but also in individual rooms of a building or sections of a vehicle, such as the passenger cabins of a ship. The extracted fluid samples are guided along the pipe and / or hose line, following a flow path, to the particle detection unit and passed through its detection area. In this application, the detection chamber is designed with a defined flow inlet and a defined flow outlet. Such an intake particle detection system is known from EP 3 584 774 A1.This discloses a particle detection unit designed as a scattered light detector, the housing or test area wall of which delimits a test area and shields it from ambient light. The test area has a flow inlet and a flow outlet. The pipe and / or hose system of the suction particle detection system is connected to the flow inlet, so that smoke particles sucked in from one (or more) monitoring areas are transported into the test area. In the test area, the smoke particles are then to be detected by means of scattered light detection, whereby light rays emitted by a light transmitter and scattered by the smoke particles are detected by a light receiver. For this purpose, a light-emitting diode or LED (Light Emitting Diode) and a photodiode are mounted on a circuit board. It is proposed that the light-emitting diode and the photodiode be mounted directly or separately as so-called surface-mounted components (SMD = Surface Mount Device).directly to the front of the circuit board. This means that the emission direction of the LED and the field of view or the incidence area of ​​the photodiode each point orthogonally away from the circuit board and therefore run parallel to each other. To protect the electrical and active, i.e. current-carrying optical components, the circuit board is also arranged outside the test area. In order to nevertheless create a detection or overlap area in the test area, within which the light beams emitted by the LED and the incidence area of ​​the photodiode overlap, optical fibers, e.g. optical fibers, should be used as passive optical components. The light beams emitted by the LED are guided into the test area by means of the optical fiber and deflected in such a way that the required detection area is created.Light rays entering an optical fiber are guided within its interior, which is why optical fibers are also called fiber optic cables. By bending the optical fibers in the desired direction, the guided light rays can be redirected as desired. A disadvantage of using optical fibers is that precise alignment of the light rays to define the detection area is difficult to achieve, especially during installation, and requires trained personnel.

[0008] Another common application in which particle detection units are used for fire detection is so-called ceiling-mounted smoke detectors, also known as point-type smoke detectors. Unlike aspirated particle detection systems, ceiling-mounted smoke detectors are mounted directly in the monitoring area, for example, on the ceiling of a room in a building.

[0009] A compact design of a ceiling-mounted smoke detector that also works according to the scattered light principle is known, for example, from US patent specification US 5,138,302. The ceiling-mounted smoke detector comprises as its essential components a cylindrical housing consisting of a base and a fitting cover. The so-called labyrinth shields the detection chamber formed inside the housing from ambient light, but allows passive exchange with the ambient air of the monitoring area. A circuit board connected to a light transmitter and a light receiver is also arranged inside the housing. The light transmitter is mounted in such a way that its radiation direction runs diagonally to the circuit board and is aimed directly at the so-called smoke monitoring zone. The light receiver, on the other hand, is also connected directly to the circuit board, so that its incidence area points orthogonally away from the circuit board.To achieve overlap between the incident field of the light receiver and the light beams of the light transmitter, a prism is used to reflect light beams scattered by smoke particles within the smoke detection zone toward the light receiver. A lens integrated into the prism focuses the reflected light beams onto the light receiver.

[0010] Unlike with fiber optics, light rays entering the prism are reflected once by an (inner) reflection surface. The light reflected by the inner reflection surface enters and exits through a separate prism surface. Any redirection of the light rays is not possible during reflection; the angle of incidence at which the light rays strike the mirror-like reflection surface is always identical to the angle of reflection or reflection.

[0011] Another ceiling smoke detector is known from patent GB 2 404 731 B. This comprises a housing with a base and a cover, as well as a circuit board and components mounted on the circuit board. The circuit board is arranged between the base and the cover of the housing, i.e. again within the detection chamber. The light receiver and an LED acting as a light transmitter are both directly connected to the circuit board, which is why their incidence and emission directions are again orthogonal to the circuit board. The light rays emitted by the LED are again deflected, in this case by 90°, into the incidence of the light receiver using a prism. For this purpose, a two-part prism carrier comprising a support base and a support cover is snapped into complementary openings in the circuit board using clips.The prism itself is inserted into the support base and held in place by the support cover, which is connected to the support base. The light receiver "looks" through an opening in the prism support at the light rays emitted by the LED and reflected by the prism's reflective surface.

[0012] With the ceiling-mounted smoke detectors disclosed in the prior art, installation, maintenance, and repair are comparatively complex due to the different optical components, the required precise alignment of these components, and the overall large number of different individual parts. Furthermore, electrical and active optical components, such as the circuit board, light transmitter, and light receiver, are located directly within the detection chamber.

[0013] Published patent application US 2018 / 0306715 A1 discloses a self-contained photosensor for detecting smoke. The photosensor comprises a light emitter, e.g., a light-emitting diode or laser diode, a light receiver implemented as a photodiode with a phototransistor, and a housing with a light exit tunnel and a light entry tunnel. The light emitter and the light receiver are each connected to their own circuit board as a surface-mounted component on the corresponding sides of the housing, so that their respective optical axes—i.e., the emission direction or direction of the incidence area—extend orthogonally to the respective circuit board and parallel to each other. To define a smoke monitoring zone within which the light beams emitted by the light emitter and the incidence area of ​​the light receiver overlap, not just one but two optical prisms are to be used in this case.The prisms are each aligned with one prism surface toward the light emitter or light receiver. A lens is arranged on another prism surface, directed toward the smoke detection area. On the light emitter side, the prism is aligned with the light entry surface toward the light emitter, while the lens arranged on the light exit surface serves to focus the light rays emitted by the light emitter and reflected by the reflection surface.

[0014] From a physical perspective, the light emitted by a light source corresponds to a large number of individual light rays that can be bundled, for example, by means of a lens along an axis of rotation or symmetry, also known as the optical axis. The light bundled along the optical axis defines a light path and is comparable to the light cone of a flashlight. For the purposes of this invention, the term “light path” is therefore understood to mean the space or area occupied by the totality of all light rays emitted by an individual light source. The light path of a light source is therefore defined by the light emitted by the light source, regardless of the actual operating state of the light source. In other words, the light path is also present if the light source is switched off, i.e. is not emitting any light.

[0015] According to US 2018 / 0306715 A1, the single lens of the optical prisms disclosed therein is intended to define such a light path along the light exit or light entry tunnel in the housing in order to create the smoke monitoring area by superimposing the light paths. To ensure the alignment of the light emitter and the light receiver to the respective reflection surface of the prisms is as precise as possible, it is proposed that the prisms be cast from transparent resin, enclosing the light emitter and light receiver, directly onto the circuit board. The disadvantages of this are the complex manufacturing process and the fact that the prisms cannot be separated from their respective circuit boards without causing damage. In the event of a defect, it is necessary to replace the entire photosensor, including the housing, circuit board, and all other optical and electrical components, which results in high maintenance and repair costs.

[0016] It is the object of the present invention to overcome the disadvantages of the prior art and in particular to create a compact particle detection unit which enables simple and precise alignment of the optical components to one another, error-free assembly which can also be carried out by untrained personnel or in an automated manner, as well as cost-effective maintenance and production by using as few (different) individual parts as possible.

[0017] The object is achieved by an optical prism for a particle detection unit according to claim 1, a housing with two prism seats according to claim 9 and a particle detection unit according to claim 15 with such a housing and two optical prisms.

[0018] An optical prism according to the invention of the type described in more detail above is characterized in that the first prism surface has a first lens and the second prism surface has a second lens, which are designed to define an inner light path running inside the prism, so that light rays entering the interior of the prism either via the first prism surface or via the second prism surface are aligned along the inner light path onto the inner reflection surface. The first and second lenses are further designed to define an outer light path running outside the prism, so that light rays exiting the interior of the prism either via the first prism surface or via the second prism surface are aligned along the outer light path.According to the invention, it is therefore provided to arrange a lens on both the first and the second prism surface, so that regardless of whether light rays enter the interior of the optical prism via the first or the second prism surface, these light rays always follow the same or identical internal light path. Light rays originating from a light source can in principle be deflected or aligned along corresponding light paths by optical means, such as a mirror or a lens. The optical means act in both directions of the light path, so that the light path itself, in the sense of this invention, is directionless. Only the light rays emitted by a light source then have a fixed direction and can follow the light path defined by the optical means either in a first direction, i.e.entering via the first prism surface and exiting via the second prism surface, or in a second, opposite direction, ie entering via the second prism surface and exiting via the first prism surface.

[0019] Unlike the prior art, the optical prism according to the invention therefore has not just one, but a total of two lenses. With such a structure, the first and second prism surfaces, in conjunction with a light source or a light receiver of a particle detection unit, can each be used either as a light entry surface or as a light exit surface, whereby the prism according to the invention can be used on both the light transmitter side and the light receiver side. By means of the respective lenses, light rays entering via the first or second prism surface are always precisely aligned to the reflection surface, and upon exiting either via the first or second prism surface, they follow the external light path predefined by the lens provided there.

[0020] The optical prism according to the invention can therefore be used either on the light transmitter side or the light receiver side of a particle detection unit, thus increasing installation flexibility. In particular, two identical or identically constructed optical prisms can be mounted in one particle detection unit. This, in turn, results in a smaller number of different components, thus reducing potential sources of error during installation.

[0021] In its simplest form, the optical prism is three-sided, with two congruent, opposite triangular bases (a right prism) and a lateral surface composed of three rectangles. Two of the rectangles then correspond to the first and second prism surfaces, respectively, and function as the light-incoming and light-outgoing surfaces, while the third rectangle corresponds to the reflection surface. However, other prism shapes, such as square or pentagonal bases, can also be used, in straight or angled designs.

[0022] Advantageous embodiments are contained in the subclaims and are explained in more detail below.

[0023] Accordingly, in an advantageous variant of the invention, the first lens and the second lens, defining the outer light path, can each be designed to focus light rays emerging from the interior of the prism via the first prism surface or via the second prism surface, at a respective, predefined distance from the first prism surface or from the second prism surface.

[0024] This can be achieved, for example, by designing the first and second lenses as converging lenses, in particular plano-convex lenses pointing outwards from the first or second prism surface, whereby light rays exiting through the respective surface are focused and light rays entering through the respective surface are aligned parallel to one another. The focal length f of a plano-convex lens corresponds to the distance between the first or second prism surface and the focal point, i.e. the point at which the exiting light rays are focused. The curvature or aspherical parameters of the lens can be used to specify optical parameters such as the opening width or aperture or focal length f, which on the one hand allows a greater number of light rays to enter the incidence area and on the other hand allows the distance at which exiting light rays are focused to be varied as desired.The incoming light rays, however, follow a substantially parallel path, regardless of the curvature or parameters of the lens. This allows the outer light paths to be varied as needed without altering the inner light paths. Furthermore, aspherical lenses have a flatter design, reducing the size of the optical measurement setup and thus leaving more space for performing optical measurements, especially for particle detection.

[0025] In principle, it is conceivable to mirror the inner reflective surface, for example, by coating its opposite and outward-facing outer surface with a suitable (metallic) material. However, according to an exemplary inventive design, the reflection of light rays traveling within the prism at the inner reflective surface preferably occurs through total internal reflection, i.e., the light rays are completely reflected at the transition from the optically denser medium (refractive index m) to the optically less dense medium (refractive index n). Such complete reflection is also referred to as total internal reflection (TIR).For this purpose, according to an exemplary embodiment of the invention, the first lens and the second lens, which define the inner light path, are each designed such that light rays entering the interior of the prism either via the first prism surface or via the second prism surface are aligned parallel to one another and directed onto the inner reflection surface. The light rays form a fixed angle with a perpendicular line of the inner reflection surface. This angle, also referred to as the critical angle, is determined taking into account the refractive index n of the material from which the prism is made, so that the optical requirements for total internal reflection, without any coating, are met at the inner reflection surface.

[0026] One possible option would be to manufacture the optical prism from an injection-moldable polymer, such as TOPAS® COC polymer, with a refractive index of approximately m = 1.56. The adjacent medium, i.e., the ambient air, has a refractive index of approximately n2 = 1.0. Total internal reflection at the inner reflection surface of the prism could then be reliably achieved, for example, starting at a critical angle of approximately 45°. When using materials with a higher refractive index n, total internal reflection also occurs at smaller critical angles, below 45°.

[0027] According to the exemplary embodiment, the refractive index n of the prism material and the critical angle are matched in such a way that the light rays incident on the inner reflection surface are completely reflected. Because the reflection occurs on an inner reflection surface of the prism, the reflection surface is also protected from any contamination that could affect its optical properties.

[0028] The respective surfaces of the prism do not necessarily have to be flat. In particular, it can be advantageous for the reflection surface to be convex or curved to improve the reflective properties and / or additionally influence the course of the internal light path.

[0029] To ensure precise positioning of the prism in the housing of a particle detection unit during maintenance work or assembly, according to one example of the invention, the first prism surface is provided with spacers for, in particular, positive coupling to a complementary alignment means of a particle detection unit, in particular a prism seat of a housing of the particle detection unit. The spacers are preferably designed in the manner of plug-in means and are integrally connected to the prism. The complementary alignment means of the prism seat can then be implemented in the form of recesses, whereby the prism and housing, or its prism seat, interact in the manner of a "plug" and "socket." The spacers are designed such that their length corresponds to a pre-determined distance from the first prism surface.The spacers allow the prism to be self-aligned into one of the prism seats of the housing of a particle detection unit without the first lens arranged on the first prism surface coming into contact with the prism seat. The distance between the prism seat and the first lens, defined by the spacers, is maintained. Overall, the spacers significantly improve the handling of the optical prisms during assembly, especially when inserting them into the respective prism seats of a particle detection unit.

[0030] In an advantageous development of this example of the invention, the length of the spacers is equal to or less than the focal length f of the first lens. In conjunction with the particle detection unit, this ensures that, provided the prism is located in one of the prism seats, the focal point of the first lens lies on or behind the light emitter, in particular an LED, or on or behind the light receiver, in particular a photodiode, of the particle detection unit.

[0031] In this case, it may be particularly expedient for the spacers, according to an exemplary development of the inventive example, to be connected to the first prism surface outside the light paths defined by the first and second lenses.

[0032] For example, the first and second prism surfaces could each have the geometry of a square, and the lens could have a circular base inscribed within the square prism surface. The spacers can then be arranged in the four corners of the square prism surface, outside the lens and consequently also outside the optically relevant regions defining the light paths. The complete prism, including the two lenses and the spacers, can be manufactured particularly simply and cost-effectively as a single piece from an injection-moldable material, e.g., using an injection molding process. Furthermore, the single-piece design can reduce the number of prism interfaces that the light rays traveling along the light paths must pass through.For example, this eliminates the need for an interface between the lens and the prism surface, allowing for highly precise alignment of the optical components, such as the first and second lenses, the two prism surfaces, and the internal reflective surface, directly during the manufacturing process. Furthermore, reducing the interfaces also reduces susceptibility to contamination, as there are fewer surfaces overall where contamination, such as smoke particles, could accumulate.

[0033] So that the optical properties of the prism are independent of the manufacturing quality of the edges, an advantageous embodiment of the invention provides that the first lens and the second lens, which define the inner light path, are each designed in such a way that light rays entering the interior of the prism either via the first prism surface or via the second prism surface are directed so that they impinge on an inner sub-region of the inner reflective surface. The light rays traveling along the inner light paths are therefore directed by the lenses only onto the inner, in particular circular, sub-region of the reflective surface, thereby reducing its optically relevant region. The outer sub-region of the reflective surface surrounding the inner sub-region is then not relevant for the reflection of incident light rays and can therefore be used for other purposes, e.g.used to fix or align the prism within a prism seat of the housing of a particle detection unit.

[0034] Thus, according to another optional variant of the invention, it is conceivable that the prism has one or more contact areas on the outer surface opposite the inner reflection surface and facing outward. These contact areas are suitable for aligning the reflection surface using a complementary alignment means of a prism seat of a housing for a particle detection unit, and are arranged outside the light paths defined by the first lens and the second lens. Preferably, the contact areas are as small as possible in relation to the reflection surface and are located outside the optically relevant areas of the inner reflection surface, corresponding to the previously described outer sub-area.The object of the invention stated at the outset is also achieved by a housing for a particle detection unit having an upper shell and a lower shell which can be connected to one another to define a detection chamber arranged within the housing and shielded from ambient light.

[0035] According to the invention, the upper shell and the lower shell together form two prism seats, each of which is suitable for receiving an optical prism in a mutually aligned manner, in particular according to one of the previously described inventive variants. The prisms are aligned with each other by being received in the prism seats such that light paths extending outside the prisms, which are defined by light rays reflected from a respective inner reflection surface of the prism, overlap one another, defining a detection area within the detection chamber.

[0036] The upper and lower shells are preferably each formed as a single piece, so that the housing as a whole consists of just these two components: the upper shell and the lower shell. The connection between the upper and lower shells can be achieved, for example, by positively inserting or clipping them together, but also by adhesive bonding. When connected, the upper and lower shells together form the two prism seats, each of which is designed to accommodate and align an optical prism.

[0037] According to an advantageous embodiment of the housing, the prism seats each have at least one alignment means, which is arranged outside the light paths for the self-aligning reception of the prism arranged therein. The prism seats are designed symmetrically in their geometry so that an identical, structurally identical optical prism can be accommodated in each of the two prism seats. In order to define the detection area required for particle detection, the two prisms, in particular their inner reflection surfaces, must be precisely aligned with one another. The alignment means ensure that the respective prism can only be accommodated in a single position, namely the required position, by the prism seat, thus preventing installation in an incorrect position.In order not to influence the optical properties of the prism, it is advantageous that the alignment means are arranged outside the light paths.

[0038] According to an exemplary variant of the invention, a first alignment means of the prism seat can be formed as guide passages arranged outside the light paths for receiving and guiding complementary spacers, in particular plug-in elements, connected to a first prism surface of the prism. To insert the prism into a prism seat, the spacers arranged on the prism are pushed into a position penetrating the guide passages of the prism seat, thereby determining the positioning and alignment of the respective prisms with respect to the housing, in particular the detection chamber, and also with respect to one another.

[0039] According to another exemplary variant of the invention, a second alignment means of a prism seat has an alignment surface with one or more contact points located outside the light paths and arranged on the alignment surface. By the outer surface of the prism, which is opposite the reflection surface and faces outwards, bearing against the one or more contact points by means of complementary contact areas, the inner reflection surface of the prism can be aligned parallel to and at the same time spaced from the alignment surface of the prism seat. The alignment of the alignment surface, in particular its inclination, corresponds to the alignment of the inner reflection surface, which is necessary to form the detection area within the detection chamber of the housing. The contact points are arranged outside the light paths and prevent the outward-facing outer surface from coming into contact with the prism seat orcomes into direct contact with its alignment surface, thereby avoiding any impairment of the optical properties of the prism. For use in an intake particle detection system, according to an optional embodiment, the upper shell and the lower shell can jointly form a flow channel with a flow inlet and a flow outlet for forming a flow path through the detection chamber, wherein the flow channel and the prism seats are aligned with one another such that the flow path is designed to traverse the detection area.

[0040] In an advantageous development, the flow channel comprises a fluid arranged within the detection chamber to deflect a fluid flow running along the flow path. The fluid is designed such that the fluid sample entering at the flow inlet, in particular ambient air, which is to be analyzed for the presence of particles, in particular smoke particles, flows through the detection area but is guided past the prism seats and the prisms located therein without interrupting the light paths defined by the internal reflective surfaces. A suitable fluid has proven to be, for example, a flow deflection component with a trapezoidal or U-shaped profile, integrally connected to the housing.A synergistic effect can be achieved by making the focal length f of the second lenses facing the detection chamber larger than the focal length f of the first lenses facing the light receiver or light transmitter. This allows for a compact design while simultaneously providing protection against contamination by increasing the distance between the optical prisms and the fluid-flowing detection chamber.

[0041] Finally, the inventive object stated at the outset is also achieved by a particle detection unit. The particle detection unit comprises a first optical prism, a second optical prism, in particular an identical or structurally identical one, and a housing, in particular each according to one of the previously described embodiments. The housing delimits a detection chamber arranged therein and shielded from ambient light and has a first prism seat and a second prism seat, wherein a first prism is arranged within the first prism seat and a second prism is arranged within the second prism seat, and the prisms are aligned with one another. Furthermore, the particle detection unit comprises a circuit board, a light transmitter for emitting light beams in an emission direction, and a light receiver for receiving light beams incident in an incidence region of the light receiver.

[0042] According to the invention, the light transmitter with the first prism seat and the light receiver with the second prism seat are positioned cooperatively on the same circuit board. Light rays emitted by the light transmitter in the emission direction then impinge on the inner reflection surface of the first prism, passing through a first prism surface of the first prism aligned by the first prism seat. The incident area of ​​the light receiver is correspondingly directed toward the inner reflection surface of the second prism, passing through a first prism surface of the second prism aligned by the second prism seat.

[0043] The position and orientation of the light transmitter and the light receiver on their shared circuit board are adapted to the position of the two prisms determined by the prism seats, so that in particular the distance between the light transmitter and the light receiver corresponds to the distance between the two prism seats and consequently the two optical prisms. According to an advantageous embodiment, the light transmitter, e.g., one or more light-emitting diodes (LEDs), and the light receiver, e.g., one or more photodiodes (PDs), are each connected directly or immediately to the circuit board, in particular to its front side facing the housing, as a so-called SMD component (Surface Mount Device), and are arranged, for example, centrally opposite the first lens of the corresponding prism.

[0044] In an exemplary embodiment of the particle detection unit, the first prism surface of the first prism and the first prism surface of the second prism have respective spacers, in particular plug-in means. The spacers engage in a form-fitting manner in complementary third alignment means of the circuit board, which are implemented as mounting openings, or are supported on the front side of the circuit board, thereby defining a predetermined distance between the first prism surface and the light transmitter or the light receiver. The engagement of the spacers in the complementary alignment means of the circuit board ensures, on the one hand, that the circuit board, the housing, and the two prisms of the particle detection unit are correctly aligned with one another. In particular, the light transmitter and the light receiver should be arranged centrally opposite the first lens of a prism.On the other hand, it also ensures that the desired distance between the respective first lenses or prism surfaces and the light transmitter or light receiver is maintained. Preferably, the distance is smaller than or equal to the focal length f of the first lens.

[0045] To protect sensitive electrical components, according to a further variant of the invention, it is advantageous for the circuit board to be arranged outside the housing and connected to the housing. The previously described spacers of a prism extend through complementary first alignment means of the respective prism seat, implemented as guide openings, and are fixed in or supported by the third alignment means of the circuit board, implemented as mounting openings.

[0046] Preferably, the particle detection unit comprises a control module which is connected to the light transmitter and the light receiver in a signal-transmitting manner and which has a memory unit for storing programming for controlling the light transmitter and the light receiver as well as for evaluating signals based on light beams detected by the light receiver.

[0047] Finally, the particle detection unit can optionally also be a component of an intake particle detection system, in which case a flow inlet of the housing is fluidically connected to a pipe and / or hose line that opens into one or more monitoring areas via one or more intake openings for the respective extraction of a fluid, in particular an air, sample. The remaining components of the intake particle detection system and the particle detection unit could then be controlled from a common control module, or alternatively, the control module of the particle detection unit and the control module of the intake particle detection system could communicate with each other.

[0048] Further details, features, feature (sub)combinations, advantages and effects based on the invention will become apparent from the following description of a preferred embodiment of the invention and the drawings. These show in

[0049] Fig. 1 is a perspective exploded view of an exemplary embodiment of a

[0050] Particle detection unit with a circuit board, a housing and two optical prisms,

[0051] Fig. 2 is a perspective view of the upper shell and the lower shell of the housing from Figure 1, with the optical prisms located therein,

[0052] Fig. 3 is a perspective view of the first and second optical prisms together with the circuit board of Figure 1,

[0053] Fig. 4 is a schematic representation of the light paths defined by two optical prisms according to an exemplary variant of the invention,

[0054] Fig. 5 is a perspective view of the upper shell and the first optical prism from Figure 1 and in

[0055] Fig. 6 is a perspective view of the lower shell and the first optical prism of Figure 1.

[0056] The figures are merely exemplary and serve only to clarify the invention. The same elements are provided with the same reference numerals. The following paragraphs describe the invention using the example of a particle detection unit operating according to the scattered light principle for an intake particle detection system. Of course, the invention is not limited to the described use; other conceivable applications include, for example, use as a transmitted-light detector and / or in a ceiling-mounted smoke detector.

[0057] Figure 1 shows an exemplary embodiment of a particle detection unit 300 according to the invention, comprising a housing 200, a first optical prism 101, a second optical prism 102, and a circuit board 310, in a perspective exploded view along the z-axis. A light transmitter 320 (not shown in Figure 1) and a light receiver 330 are mounted on the circuit board 310 in corresponding mounting openings. For example, the light transmitter 320 can comprise one or more light-emitting diodes (LEDs), and the light receiver 330 can comprise one or more photodiodes (PDs), which, as so-called surface-mounted components (SMDs), are directly connected to the front side of the circuit board 310 facing the housing 200. The emission direction of the light transmitter 320 and the incidence area of ​​the light receiver 330 then point orthogonally away from the front side of the circuit board 310.The printed circuit board 310 is connected to the housing 200 by means of three connecting elements 311, in particular screws. On the rear side, opposite the front side of the printed circuit board 310, an optional cover plate 340 can be snapped into complementary recesses in the housing 200, for example, via spring-loaded plug-in means.

[0058] The housing 200 comprises an upper shell 210 and a lower shell 220, which are preferably each manufactured as a single piece, so that the housing 200 consists of exactly two components. The upper shell 210 and the lower shell 220 are connectable to one another, forming a detection chamber 230 and a first prism seat 241 and a second prism seat 242 inside the housing. The upper shell 210 and the lower shell 220 can be connected using conventional fasteners such as screws or the like, or by means of an adhesive bond. The embodiment of a particle detection unit 300 shown in Figure 1 is suitable for use in an intake particle detection system, which is why the upper shell 210 and the lower shell 220 together also form a flow channel 250 with two inlet and outlet openings defining an intermediate flow path, the flow inlet 251 and the flow outlet 252.The prism seats 241, 242 are provided for receiving and aligning the first optical prism 101 and the second optical prism 102, respectively. As shown here, the first and second prisms 101, 102 are preferably structurally identical, which significantly simplifies assembly.

[0059] Figure 2 shows the upper shell 210 and the lower shell 220 of the housing 200 from Figure 1 in a position folded open towards each other. The first optical prism 101 and the second optical prism 102 are each received in a prism seat 241, 242 and aligned such that their respective outer light paths L2 overlap one another, defining a detection area DB within the detection chamber 230 (see also Figure 4). The optical prisms 101, 102 each point with a first prism surface 110 in the direction of the upper shell 210 or the circuit board 310 (see Figure 1). In addition, four spacers 112 are formed integrally on the first prism surface 110. Two of the spacers 112 of a prism 101, 102 are shaped in the manner of plug-in means for positive engagement in complementarily arranged mounting openings of the printed circuit board 310.

[0060] The flow channel 250, the detection chamber 230, and the two prism seats 241, 242 of the housing 200 are generally symmetrical with respect to the z-axis (see Figure 1), so that the flow inlet 251 and outlet 252, as well as the light transmitter and light receiver sides of the housing 200 and the optical prisms 101, 102 themselves, are not yet defined. Only by connecting the pipe and / or hose line of an intake particle detection system to one of the two inlet or outlet openings of the flow channel 250 is this defined as the flow inlet 251. The first prism seat 241, which is then located upstream in the direction of the fluid flow, can optionally be assigned to the light transmitter 320 or the light receiver 330 and the second prism seat 242, which is located downstream in the direction of the fluid flow, can be assigned conversely to the light receiver 330 or the light transmitter 320 by connecting the light transmitter 320 or the light receiver 330 to the circuit board 310.Light receiver 330 is arranged opposite the respective prism seat 241, 242 (see also Figure 1).

[0061] Deviating from this, in the present, optional embodiment, the flow channel 250 is provided, for example, with a predefined flow inlet 251 and a predefined flow outlet 252, wherein the flow path therebetween leads through the detection chamber 230 and the detection region DB. The first prism seat 241, which is located upstream in the direction of the fluid flow, is assigned to the light transmitter 320, and the second prism seat 242, which is located downstream in the direction of the fluid flow, is assigned to the light receiver 330 (see Figure 1). Arranged within the flow channel 250 and in the region of the detection chamber 230 is a fluid 253 in the form of a flow deflection component having a U-profile, which ensures that particles transported in the fluid flow, in particular dirt or dust particles orIn the event of a fire, smoke particles are also redirected in such a way that contamination caused by particle deposits in the area of ​​the outer light paths L2 and the optical components, in particular the two optical prisms 101, 102, is avoided or at least minimized. By using aspherical lenses, their focal lengths f and thus the outer light paths can be varied. Preferably, the focal length f of the second lenses 121 facing the detection area DB is greater than the focal length f of the first lenses facing the light receiver or the light transmitter, whereby a compact design and, at the same time, protection against contamination is achieved by increasing the distance between the optical prisms 101, 102 and the detection area DB through which fluid flows. In the area of ​​the flow outlet 252, a nozzle 254 is arranged within the flow channel 250, which nozzle enables an air flow measurement based on a differential pressure sensor.

[0062] In Figure 3, the first optical prism 101 and the second optical prism 102 are shown in a perspective individual view fixed in mounting openings of the circuit board 310. The housing 200, in particular the upper shell 210 arranged between the circuit board 310 and the prisms 101, 102 (see Figure 1), are hidden for clarity. It can be clearly seen that the first and second optical prisms 101, 102 are of the same construction or identical, and are rotated relative to one another about their longitudinal axes, enclosing the so-called scattered light angle. This alignment of the prisms 101, 102 relative to one another, which is typical for a scattered light detector, is to be understood purely as an example. As an alternative, the prisms 101, 102 could, for example, be arranged opposite one another in the embodiment of a transmitted light detector. Possible directions of rotation orThe scattered light angles of the two prisms 101, 102 relative to each other are predetermined by third alignment means 313 designed as mounting openings on the circuit board 310. In the example shown, the circuit board 310 has two such mounting openings for each of the prisms 101, 102. Between these two mounting openings, a further mounting opening is arranged for accommodating the light transmitter 320, in particular a light-emitting diode, or the light receiver 330, in particular a photodiode.

[0063] In the embodiment shown here, the prisms 101, 102 are formed from two congruent, opposite base surfaces designed as a right-angled, isosceles triangle, and a lateral surface composed of two square and one rectangular surface portions. The two square surface portions of the lateral surface correspond to a first prism surface 110 and a second prism surface 120, which function as light entry or exit surfaces. Light rays entering the interior of the prism 101, 102 via the first or second prism surface 110, 120 are reflected by an internal reflection surface 130 corresponding to the rectangular surface portion of the lateral surface and exit from the interior of the prism 101, 102 via the other prism surface 110, 120.

[0064] A first lens 111 is arranged on the first prism surface 110, and a second lens 121 is arranged on the second prism surface 120. The two lenses 111, 121 are each shaped as plano-convex converging lenses, pointing outwards from the first and second prism surfaces 110, 120, respectively, and comprise a circular base area that is inscribed in the square base area of ​​the first and second prism surfaces 110, 120, respectively. The lenses 111, 121 shown here are aspherical, but completely spherical lenses could of course also be used. The first prism surface 110 of a respective prism 101, 102 is arranged opposite the circuit board 310 and has a total of four spacers 112 in its four corners, positioned outside the circular base area of ​​the first lens 111.Preferably, the prism 101, 102, the respective lenses 111, 121 and the spacers 112 are manufactured in one piece by means of an injection molding process.

[0065] The spacers 112 define the distance to the circuit board 310 and consequently to the light transmitter 320 or light receiver 330 mounted thereon. Preferably, the length of a spacer 112 is equal to or less than the focal length f of the first lens 111, so that its focal point lies on or behind the light transmitter 320 or the light receiver 330. Two of the four spacers 112 of a prism 101, 102 are designed in the manner of plug-in means (see also Figure 2) for positive engagement in the third alignment means 313 of the circuit board 310, here the complementarily arranged mounting openings, and can be fixed therein. By means of the spacers 112 designed as plug-in means and the third alignment means 313, the respective prism 101, 102 can be connected to the circuit board 310 in basically two positions or directions of rotation.According to an optional embodiment not shown here, it is alternatively also conceivable to construct the four spacers 112 so differently that the respective prism 101, 102 can be connected to the circuit board 310 in only one single position or direction of rotation.

[0066] A schematic representation of the light paths L1, L2 defined by two optical prisms 100 according to an exemplary variant of the invention can be seen in Figure 4. The respective first prism surfaces 110 are arranged opposite the light transmitter 320 or the light receiver 330 in such a way that the light receiver 330 "looks" orthogonally through the first prism surface 110 into the interior of the prism 100, and light rays emitted by the light transmitter 320 follow an outer light path L2 defined by the light transmitter 320, orthogonally through the first prism surface 110 and enter the interior of the prism 100. The first lens 111 arranged on the first prism surface 110 aligns the light rays entering there parallel to one another and along the inner light path L1 onto an inner partial region 131 of the inner reflection surface 130.The outer portion of the reflection surface 130 surrounding the inner portion 131 and not being optically relevant can be used to align the prism 100 and, for this purpose, has corresponding contact areas 132 on the outer surface arranged opposite the reflection surface 130 and facing outwards. In the example shown, the light rays impinge on it at a critical angle of 45° with a perpendicular line of the inner reflection surface 130 and are reflected completely at a reflection angle of 45° with the perpendicular line, also including the perpendicular line, in the direction of the second prism surface 120, continuing to follow the inner light path L1. The second lens 121 focuses light rays emerging from the prism 100 via the second prism surface 120 along the outer light path L2.Both prisms 100 are aligned with each other such that the outer light paths L2 emanating from the second prism surface 120 overlap, thus defining the detection area DB. In this way, light rays scattered by particles located in the detection area DB can be detected by the light receiver 330 following the light paths L1, L2.

[0067] Figure 5 shows a perspective view of the upper shell 210 from Figure 1. For reasons of clarity, only the first optical prism 101 is shown here; the remaining components of the particle detection unit 300 are hidden. The first alignment means 211 of the first and second prism seats 241, 242 formed in the upper shell 210 are clearly visible. The first alignment means 211 are each implemented in the form of four guide passages, which, in the operating state, when the prisms 101, 102 are received and aligned by the respective prism seat 241, 242, are penetrated by the complementarily arranged spacers 112 of the respective prism 101, 102. Between the first alignment means 211, a further opening is formed for the passage of the light beams transmitted by the light transmitter 320 or received by the light receiver 330.

[0068] A perspective view of the lower shell 220 from Figure 1 is shown in Figure 6. Again, the remaining components of the particle detection unit 300, with the exception of the first optical prism 101, are masked out. A second alignment means 222 of each of the first and second prism seats 241, 242 is formed by the lower shell 220. The second alignment means 222 comprises a rectangular alignment surface 221, the dimensions of which correspond to the dimensions of the inner reflection surface 130 of the prisms 101, 102, as well as three lateral walls adjacent thereto.

[0069] In the embodiment of a scattered light detector, the alignment surfaces 221 are aligned with each other to include the desired scattered light angle and are inclined so that the inner reflection surfaces 130 of the two prisms 101, 102, which run parallel thereto, define a detection area DB (see Figure 4) within the detection chamber 230 delimited by the upper shell 210 and the lower shell 220 by superimposing light paths L1, L2 defined by light rays reflected at the reflection surfaces 130. In order to prevent the outer surface of the prisms 101, 102, which is opposite the reflection surface 130 and faces outwards, from coming into direct contact with the alignment surface 221, the latter has a total of four contact points 223 arranged in the corner regions of the alignment surface 221, on which corresponding contact regions 132 (see again Figure 4) are supported when the optical prism 101, 102 is inserted.

[0070] The second alignment means 222, in particular its alignment surface 221 together with the three lateral walls, ensures that the respective prism 101, 102 can be inserted into the prism seats 241, 242 exclusively in a single position, which corresponds to the desired positioning and alignment relative to the light transmitter 320 or light receiver 330 and to the respective other prism 101, 102. The spacers 112 establish the desired distance from the circuit board 130, in particular from the light transmitter 320 or light receiver 330 mounted thereon (see also Figure 3). The integrally formed upper and lower shells 210, 220 ensure that the detection area (DB) is formed in relation to the prism seats 241, 242 at the desired position within the detection chamber 230 and is preferably flowed through by the fluid flow running along the flow channel 250.During assembly or maintenance work, the alignment means 211, 222, 313 enable a self-aligning reception of a respective identical or identically constructed prism 101, 102 by the prism seats 241, 242.

[0071] List of reference symbols:

[0072] 100 optical prism

[0073] 101 first optical prism

[0074] 102 second optical prism

[0075] 110 first prism surface

[0076] 111 first lens

[0077] 112 spacers

[0078] 120 second prism surface

[0079] 121 second lens

[0080] 130 internal reflection surface

[0081] 131 inner section

[0082] 132 Investment area

[0083] 200 housings

[0084] 210 upper shell

[0085] 211 first alignment tool

[0086] 220 lower shell

[0087] 221 alignment surface

[0088] 222 second alignment tool

[0089] 223 Investment point

[0090] 230 Detection chamber

[0091] 241 first prism seat

[0092] 242 second prism seat

[0093] 250 flow channel

[0094] 251 Flow inlet

[0095] 252 Flow outlet

[0096] 253 Fluids

[0097] 254 nozzle

[0098] 300 particle detection unit

[0099] 310 circuit board

[0100] 311 connecting element

[0101] 313 third alignment means

[0102] 320 light transmitter 330 light receiver

[0103] 340 cover plate

[0104] DB detection area L1 inner light path

[0105] L2 outer light path z z-axis of the particle detection unit

Claims

Patent claims:

1. An optical prism (100, 101, 102) for a particle detection unit (300), which prism (100, 101, 102) comprises a first prism surface (110) and a second prism surface (120), via which light rays can enter or exit the interior of the optical prism (100, 101, 102), as well as an internal reflection surface (130) which reflects light rays running inside the optical prism (100, 101, 102) and incident thereon, characterized in that the first prism surface (110) has a first lens (111) and the second prism surface (120) has a second lens (121), which are designed to define an internal light path (L1) running inside the prism (100, 101, 102), so that either via the first prism surface (110) or via the second prism surface (120) into the interior of the prism (100, 101,102) are aligned along the inner light path (L1) onto the inner reflection surface (130), and which are designed to define an outer light path (L2) extending outside the prism (100, 101, 102), so that light rays emerging from the interior of the prism (100, 101, 102) either via the first prism surface (110) or via the second prism surface (120) are aligned along the outer light path (L2).

2. Prism (100, 101, 102) according to claim 1, characterized in that the first lens (111) and the second lens (121), defining the outer light path (L2), are each designed to focus light rays emerging from the interior of the prism (100, 101, 102) via the first prism surface (110) or via the second prism surface (120), at a respective, predetermined distance from the first prism surface (110) or from the second prism surface (120).

3. Prism (100, 101, 102) according to claim 1 or 2, characterized in that the first lens (111) and the second lens (121), defining the inner light path (L1), are each designed such that light rays entering the interior of the prism (100, 101, 102) either via the first prism surface (110) or via the second prism surface (120) run parallel to one another and are aligned with the inner reflection surface (130) at a predetermined critical angle with a normal line of the inner reflection surface (130), wherein the refractive index n of the material from which the prism (100, 101, 102) is made and the critical angle included with the inner reflection surface (130) are determined relative to one another in such a way that the light rays are completely reflected by the inner reflection surface (130) under total internal reflection.

4. Prism (100, 101, 102) according to one of the preceding claims, characterized in that the first prism surface (110) is provided with spacers (112) for in particular form-fitting coupling with a complementary alignment means (211, 313) of a particle detection unit (300), in particular a prism seat (241, 242) of a housing (200) of a particle detection unit (300), wherein the spacers (112) are designed such that their length corresponds to a pre-determinable distance from the first prism surface (110).

5. Prism (100, 101, 102) according to claim 4, characterized in that the length of the spacers (112) is equal to or less than the focal length f of the first lens (111).

6. Prism (100, 101, 102) according to one of claims 4 or 5, characterized in that the spacers (112) are connected to the first prism surface (110) lying outside the light paths (L1, L2) defined by the first lens (111) and the second lens (121).

7. Prism (100, 101, 102) according to one of the preceding claims, characterized in that the first lens (111) and the second lens (121), defining the inner light path (L1), are each designed such that light rays entering the interior of the prism (100, 101, 102) either via the first prism surface (110) or via the second prism surface (120) are aligned so as to impinge on an inner partial region (131) of the inner reflection surface (130).

8. Prism (100, 101, 102) according to one of the preceding claims, characterized in that the prism (100, 101, 102) has one or more contact areas (132) on the outer surface opposite the inner reflection surface (130) and facing outwards, which contact areas are suitable for aligning the reflection surface (130) using a complementary alignment means (222) of a prism seat (241, 242) of a housing (200) for a particle detection unit (300), and are arranged outside the light paths (L1, L2) defined by the first lens (111) and the second lens (121).

9. Housing (200) for a particle detection unit (300), which housing (200) has an upper shell (210) and a lower shell (220) which can be connected to one another to delimit a detection chamber (230) arranged within the housing (200) and shielded from ambient light, characterized in that the upper shell (210) and the lower shell (220) together form two prism seats (241, 242) for receiving an optical prism (100, 101, 102) in a mutually aligned manner, in particular according to one of the preceding claims, so that light paths (L2) extending outside the prisms (100, 101, 102), which are defined by light rays reflected at a respective inner reflection surface (130) of the prism (100, 101, 102), form a detection area (DB) within the Detection chamber (230) defining each other are aligned superimposed.

10. Housing (200) according to claim 9, characterized in that the prism seats (241, 242) each have at least one alignment means (211, 222) which is arranged outside the light paths (L1, L2) for the self-aligning reception of the respective prism (100, 101, 102).

11. Housing (200) according to one of claims 9 or 10, characterized in that a first alignment means (211) of a prism seat (241, 242) is realized as guide passages which are arranged outside the light paths (L1, L2) for receiving and guiding complementary spacers (112) connected to a first prism surface (110) of the prism (100, 101, 102).

12. Housing (200) according to one of claims 9 to 11, characterized in that a second alignment means (222) of a prism seat (241, 242) has an alignment surface (221) with one or more contact points (223) located outside the light paths (L1, L2) and arranged on the alignment surface (221), so that the inner reflection surface (130) of the prism (100, 101, 102) can be aligned parallel and spaced from the alignment surface (221) by an outer surface of the prism (100, 101, 102) opposite the reflection surface (130) and facing outwards resting on the one or more contact points (223) by means of complementary contact areas (132).

13. Housing (200) according to one of claims 9 to 12, characterized in that the upper shell (210) and the lower shell (220) together form a flow channel (250) with a flow inlet (251) and a flow outlet (252) for forming a flow path running through the detection chamber (230), wherein the flow channel (250) and the prism seats (241, 242) are aligned with one another in such a way that the flow path is designed to cross the detection area (DB).

14. Housing (200) according to claim 13, characterized in that the flow channel (250) has a flow means (253) which is arranged to deflect a fluid flow running along the flow path within the detection chamber (230).

15. Particle detection unit (300) with a first optical prism (101) and a second optical prism (102), each according to one of claims 1 to 8, a housing (200) according to one of claims 9 to 14, which housing (200) delimits a detection chamber (230) arranged therein and shielded from ambient light and has a first prism seat (241) and a second prism seat (242), wherein the prisms (101, 102) are each arranged within a prism seat (241, 242) and aligned with one another, a circuit board (310) and a light transmitter (320) for emitting light beams in an emission direction and a light receiver (330) for receiving light beams incident in an incidence region of the light receiver (330), characterized in that the light transmitter (320) is connected to the first prism seat (241 ) and the light receiver (330) are positioned cooperating with the second prism seat (242) on the same circuit board (310),so that light rays emitted by the light transmitter (320) in the emission direction pass a first prism surface (110) of the first prism (101) aligned by the first prism seat (241) and impinge on its inner reflection surface (130), and the incidence area of the light receiver (330) is aligned passing a first prism surface (110) of the second prism (102) aligned by the second prism seat (242) and impinges on its inner reflection surface (130).

16. Particle detection unit (300) according to claim 15, characterized in that the first prism surface (110) of the first prism (101) and the first prism surface (110) of the second prism (102) have respective spacers (112) which maintain a predetermined distance between the first Prism surface (110) and the light transmitter (320) or the light receiver (330) engage in complementary third alignment means (313) of the circuit board (310), in particular in a form-fitting manner.

17. Particle detection unit (300) according to claim 16, characterized in that the printed circuit board (310) is arranged outside the housing (200) and is connected to it, wherein the spacers (112) are guided through complementary first alignment means (211) of the respective prism seat (241, 242), which are realized as guide passages, and are fixed in the third alignment means (313) of the printed circuit board (310) or are supported on the printed circuit board (310).

18. Particle detection unit (300) according to one of claims 15 to 17, characterized in that the particle detection unit (300) comprises a control module connected to the light transmitter (320) and the light receiver (330) in a signal-transmitting manner, which control module has a memory unit for storing programming for controlling the light transmitter (320) and the light receiver (330) and for evaluating signals based on light beams detected by the light receiver (330).

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