Washing machine or dishwasher with an optical sensor

Abstract

washing machine or dishwasher with an optical sensor (10), wherein the optical sensor (10) comprises - a case (20), - a light-emitting element (40), - a light-receiving element (42), - a light guiding structure (48) made of a transparent material with a light entry point, a first reflective surface (56), a second reflective surface (58) and a light exit point, wherein the light-emitting element (40), the light-receiving element (42) and the light-guiding structure (48) define a light measurement path (16) which runs in this order from the light-emitting element (40) via the light entry point, the first reflective surface (56), the second reflective surface (58) and the light exit point to the light-receiving element (42), wherein the light measurement path (16) runs on a section (18) located between the first (56) and the second (58) reflective surface outside the housing (20), wherein the light traveling along the light measurement path (16) from the light-emitting element (40) to the light-receiving element (42) is reflected at the first reflective surface (56) and at the second reflective surface (58), characterized by the fact that the light-emitting element (40) and the light-receiving element (42) are arranged outside the light-guiding structure (48) at a distance from it, wherein the entry point (60) and the exit point (62) each have a converging lens function, wherein a divergent light beam coming from the light-emitting element (40) is converted into a substantially parallel light beam by the converging lens function of the entry point (60), this parallel light beam is then reflected at the first (56) and the second (58) reflecting surface and subsequently converted into a convergent light beam directed towards the light-receiving element (42) by the converging lens function of the exit point (62), and wherein a light beam extending from the first reflective surface (56) to the second reflective surface (58) has a cross-sectional area of ​​not less than 0.9 mm at every point of the section (18) of the light measurement path (16) extending outside the housing (20). 2 exhibits.

Description

[0001] The present disclosure relates to an optical sensor intended for use in a household washing machine or dishwasher.

[0002] Optical sensors of the type considered here can be used, in particular, as turbidity sensors to determine the turbidity of the wash water in a washing machine or dishwasher. The turbidity can then be used to infer the degree of soiling of the laundry or dishes to be cleaned. To measure the turbidity of the wash water, part of a light measurement path defined by the sensor runs outside the sensor through a wash chamber of the machine, through which the wash water flows. Light emitted by the sensor along this measurement path is attenuated on this portion of the path outside the sensor, the attenuation of which depends on the turbidity of the wash water.

[0003] The term "wash water" here refers to any washing liquid used for cleaning laundry or dishes. Besides water, the washing liquid typically contains various additives, especially cleaning agents, but also fabric softener or other supporting substances.

[0004] Regarding the prior art of optical sensors that can be used as turbidity sensors, reference is made, for example, to WO 2006 / 050767 A2. US 2009 / 0 140 754 A1 discloses another turbidity sensor in whose housing a light guide structure is provided, comprising a light entry point, a first reflective surface, a second reflective surface, and a light exit point. The light guide structure, together with a light-emitting element and a light-receiving element, defines a light measurement path, a portion of which extends outside the housing. DE 38 21 543 A1 discloses a method for the simultaneous measurement of the turbidity and particle concentration of liquids, wherein a light guide bundle with a cross-sectional area of ​​a few square millimeters is used for turbidity measurement.WO 91 / 16 618 A1 discloses an optical sensor for measuring characteristic properties of liquids, in which a light beam exiting an optical fiber is guided via a reflective surface into a sample chamber and subsequently deflected via another reflective surface into a further optical fiber. A converging lens may be arranged between the reflective surface and the optical fiber, or between the further reflective surface and the further optical fiber.

[0005] One task is to provide an optical sensor that can be used as a turbidity sensor in a washing machine or dishwasher, whose sensor output signal is comparatively less susceptible to interference.

[0006] A washing machine or dishwasher is provided with an optical sensor according to the features of claim 1. Advantageous embodiments are described in the dependent claims.

[0007] According to one aspect, the optical sensor comprises a housing, a light-emitting element, a light-receiving element, and a light-guiding structure made of a transparent material with a light-entry point, a first reflective surface, a second reflective surface, and a light-emission point. The light-emitting element, the light-receiving element, and the light-guiding structure define a light measurement path, which runs in this order from the light-emitting element, through the light-entry point, the first reflective surface, the second reflective surface, and the light-emission point, to the light-receiving element.The light measurement path runs along a section outside the housing between the first and second reflective surfaces, whereby the light traveling along the light measurement path from the light-emitting element to the light-receiving element undergoes total internal reflection at both the first and second reflective surfaces. A light beam traveling from the first to the second reflective surface has a cross-sectional area of ​​at least 0.9 mm² at every point along the section of the light measurement path extending outside the housing. 2 on.

[0008] In domestic washing machines and dishwashers, numerous foreign particles (dirt particles) can be present in the wash water, detaching from the items being cleaned. Furthermore, foam formation is frequently observed in the wash water, which can be caused or intensified by cleaning additives, for example. When such particles and foam bubbles cross the light measurement path, this can lead to a temporary drop in the sensor output signal because the emitted light is scattered or absorbed by the particles and foam bubbles. When the particle or foam bubble is flushed out of the light measurement path, the sensor output signal rises again to its previous value. Depending on the size of the particles and foam bubbles, the sensor output signal can drop more or less significantly. Such temporary drops represent disruptive noise in the sensor output signal.It has been shown that by using a certain minimum size for the light beam traveling from the first to the second reflective surface, the interfering influence of particles and foam bubbles crossing the light measurement path can be reduced. Preferred values ​​for the cross-sectional area of ​​the light beam traveling from the first to the second reflective surface are, in this order, 1.5 mm. 2 , 2.0 mm 2 , 2.5 mm 2 and 3.0 mm 2 .

[0009] The beam of light running from the first reflective surface to the second reflective surface is essentially a parallel beam.

[0010] The entry and exit points each have a converging lens function. A divergent light beam coming from the light-emitting element is transformed by the converging lens function of the entry point into an essentially parallel light beam.

[0011] A substantially parallel beam of light coming from the second reflective surface is transformed by the converging lens function of the exit point into a convergent beam of light directed towards the light-receiving element.

[0012] Preferably, the first reflective surface and / or the second reflective surface is a flat surface.

[0013] Preferably, the light guide structure is formed from a single, continuous light guide body.

[0014] The light-emitting element and the light-receiving element are arranged outside the light-guiding structure at a distance from it.

[0015] A divergent beam of light coming from the light-emitting element is transformed by the converging lens function of the entry point into an essentially parallel beam of light, whereby this parallel beam of light is then reflected at the first and second reflecting surfaces and subsequently transformed by the converging lens function of the exit point into a convergent beam of light directed towards the light-receiving element.

[0016] Preferably, when only air is present on the section of the light measurement path running outside the housing, the radiant energy of the light arriving at the light-receiving element is at least 50 percent of the radiant energy of the light emitted by the light-emitting element in the direction of the entry point. More preferably, this proportion is at least 60 percent, and even more preferably at least 65 percent.

[0017] According to yet another aspect, the invention provides an optical sensor comprising a housing with an interior space and a measuring assembly arranged in the interior space, comprising a light-emitting element and a light-receiving element, wherein the measuring assembly defines a light measurement path extending from the light-emitting element to the light-receiving element, which runs outside the housing for part of its length. The light-emitting element and the light-receiving element are jointly arranged in a first sub-space of the housing interior, and the light measurement path runs through at least a second sub-space of the housing interior, which is sealed off from the first sub-space, for part of its length.Preferably, all electrical / electronic components of the sensor are housed in the first compartment, such as evaluation electronics arranged on a common circuit board with the light-emitting and light-receiving elements. This ensures reliable protection against the ingress of washing water into the sensor areas where the electrical / electronic components of the sensor, including the light-emitting and light-receiving elements, are located. Sealing the first compartment from the at least one second compartment prevents any potential ingress of washing water into the second compartment from causing a malfunction or even a failure of the sensor's electrical function.

[0018] The at least one second compartment is expediently formed in a housing area designed for immersion in a liquid-flushed chamber. For optimal protection of the components of the measuring assembly housed in the first compartment, the first compartment is preferably limited only by those wall sections of the housing that, when the optical sensor is installed as intended, are free from a liquid environment. This prevents wash water from entering the first compartment from outside the housing, bypassing the sealing point between the first and second compartments, for example, through a housing perforation unintentionally created during assembly or use.

[0019] In a preferred embodiment, the measuring assembly comprises a light guide structure made of a transparent material, which guides the light along a portion of the light measurement path. The light guide structure has an entry point open into the first sub-space for a light beam coming from the light-emitting element and / or an exit point open into the first sub-space for a light beam directed towards the light-receiving element. Furthermore, it projects into at least one second sub-space. The light guide structure preferably has two reflective surfaces, which serve for total internal reflection of the light guided along the light measurement path.A light beam directed from the light-emitting element towards the entry point of the at least one light guide travels within the light guide structure to one of the two reflective surfaces. There, it undergoes total internal reflection towards the second reflective surface, with the section of the light measurement path located outside the housing situated between the two reflective surfaces. At the second reflective surface, the light beam undergoes another total internal reflection and is then guided within the light guide structure to the exit point, from where it reaches the light-receiving element.

[0020] To seal the first compartment from at least one second compartment, the light guide structure can be sealed against the housing. For example, a separate sealing element can be provided between the light guide structure and the housing to seal the light guide structure against the housing. It is understood that, instead of a separate sealing element, a sealing element manufactured integrally with the light guide structure can be used. Standard two-component injection molding techniques readily allow the production of a light guide structure with an integrally molded sealing element, which may be made of a softer material than the light guide structure itself. Furthermore, it is also conceivable to achieve the desired seal between the light guide structure and the housing by bonding the light guide structure into the housing, with the adhesive joint ensuring the required seal.Furthermore, it is conceivable to achieve the desired tightness by means of a press fit of the light guide structure in the housing or by means of a welded connection.

[0021] According to a preferred embodiment, the housing comprises a pot-shaped main body with a shell and a base featuring several protrusions. The light-guiding structure has a base and two extensions integrally connected to the base, each projecting into one of the protrusions. To seal the first of the at least two sub-compartments, the base of the light-guiding structure can be sealed against the shell of the main body. For this purpose, it is recommended that the base of the light-guiding structure substantially fills the inner cross-section of the shell. For example, the base of the light-guiding structure can have a circular outline and be located in a correspondingly circular-cylindrical region of the shell.

[0022] As an alternative to installing the light guide structure in a sealed manner relative to the housing, it is conceivable to provide a separating membrane, transparent to the measuring light and separate from the light guide structure, which extends across the interior of the housing and seals the first sub-space from at least one second sub-space.

[0023] Although the discussion of the light guide structure, which is manufactured using an injection molding process, has so far only referred to a first and a second reflective surface, it is understood that the light guide structure can have more than two reflective surfaces for redirecting the light supplied by the light-emitting element and coupled into the light guide structure. It is entirely conceivable that the light guided in the light guide structure is redirected by a reflective surface at three or more points before exiting the light guide structure at the exit point and reaching the light-receiving element. Therefore, there is no intention to limit the light guide structure to having only two reflective surfaces in total.

[0024] It should also be noted that the deflection of the light at the reflective surfaces can be achieved, for example, by means of a mirrored design of the reflective surfaces, instead of by total internal reflection. Accordingly, the invention is not intended to be limited to total internal reflection of the light at the reflective surfaces. It is sufficient if the reflective surfaces are designed in such a way that a deflection of the light beam guided in the light-guiding structure takes place at them.

[0025] Preferred embodiments are explained in detail below with reference to the accompanying drawings. These depict: Fig. 1 an axial longitudinal section through an optical sensor according to a first embodiment, Fig. 2 a cross-sectional view of the sensor of the Fig. 1 according to line AA, Fig. 3 schematically an axial longitudinal section through an optical sensor according to a second embodiment.

[0026] The one in the Fig. 1 and Fig. The optical sensor shown in Figure 2 - generally referred to as 10 - is used as a turbidity sensor in a domestic washing machine or dishwasher. Fig. Figure 1 shows the installation situation of the sensor 10, which is inserted into a mounting opening (not further specified) in a wall 12 that defines a wash chamber 14, through which the wash water used to clean laundry or dishes is flushed. The sensor 10 emits light along a light measurement path (light measurement path) indicated by a dashed line at 16, a section 18 of which runs outside the sensor through the wash chamber 14. On this section, the light is attenuated depending on the degree of contamination (turbidity) of the wash water, and the degree of attenuation indicates the degree of contamination of the items to be cleaned (laundry, dishes).

[0027] The sensor 10 comprises a housing 20 with an approximately pot-shaped main body 22 and a lid 24 placed on the pot opening. The main body 22 has a pot shell 26 and a pot base 28. The pot axis of the pot-shaped main body 22, designated 30, forms an axis of the housing 20. The pot base 28 has several (here two) axially projecting protrusions 32, 34, which, in the installation position of the sensor 10, extend into the wash chamber 14. The protrusions 32, 34 can be identical or different in design. In the example shown, protrusion 34 has a greater axial length than protrusion 32, because a temperature sensor 36 is housed in protrusion 34, which serves to detect the temperature of the wash water in the wash chamber 14.

[0028] The housing 20 of the sensor 10 contains a measuring assembly, generally designated 38, which comprises a light-emitting diode 40 and a photodiode 42. It is understood that other types of light-emitting and light-receiving elements can be used instead of the light-emitting diode 40 and the photodiode 42. The light-emitting diode 40 and the photodiode 42 are both arranged on a circuit board 44, which may also house other electrical / electronic components. The circuit board 44 has an electrical connector 46, via which the sensor 10 can be electrically connected to a control unit of the washing machine or dishwasher.

[0029] The measuring assembly 38 further comprises a light guide structure made of a highly transparent material, for example polycarbonate, which here is formed by a single light guide body 48. The light guide body 48 has a base part 50 and two light guide fingers 52, 54 projecting axially from the base part 50. Each of the light guide fingers 52 projects into one of the protrusions 32, 34 and is surrounded by air on at least a predominant part of its outer surface, i.e., not in contact with the wall of the housing 20. At their free ends projecting into the protrusion, the light guide fingers 52, 54 each have a reflective surface 56 or 58, respectively, which here is designed as a planar surface and forms an optical interface between the material of the light guide body 48 and the air, causing total internal reflection of the light traveling along the light measuring path 16.

[0030] On the base part 50 of the light guide body 48, two converging lenses 60, 62 are integrally formed in approximately opposite positions to the light-emitting diode 40 and the photodiode 42. These lenses form an entry point for a light beam coming from the light-emitting diode 40 and an exit point for a light beam coming from the light guide body 48. The converging lens 60 has such a characteristic that it approximately parallelizes the divergent light beam coming from the light-emitting diode 40, so that a parallel light beam travels in the light guide finger 52 of the light guide body 48, the cross-sectional area of ​​which corresponds approximately to that of the light guide finger 52. Accordingly, the reflective surface 56 provided at the free end of the light guide finger 52 is essentially completely illuminated with light.The incoming parallel beam is totally reflected from the reflective surface 56 and exits through the housing wall of the protrusion 32 into the wash chamber 14. After passing through the path section 18, this parallel beam passes through the housing wall of the protrusion 34 and enters the light guide finger 54. There, it is totally reflected at the reflective surface 58 and guided along the light guide finger 54 towards the converging lens 62. The converging lens 62 transforms the parallel beam into a convergent beam of light directed towards the photodiode 42.

[0031] In its lower axial region, the cup shell 26 of the main housing body 22 has an annular circumferential axial shoulder 64 that projects radially inwards. This shoulder serves as a seat for an external sealing element 66 that seals the sensor housing 20 against the mounting wall 12. The external sealing element 66 can, for example, be a separate sealing element or it can be formed integrally with the main housing body 22, for instance, using a two-component injection molding process. The external sealing element 66 prevents wash water from the wash chamber 14 between the housing 20 and the mounting wall 12 from entering the (dry) space beyond the mounting wall 12.

[0032] On the inside of the sensor, the base part 50 of the light guide body 48 essentially completely fills the inner cross-section of the main housing body 22, being sealed against the main housing body 22 by a ring-shaped, circumferential internal sealing element 68. This internal sealing element 68 can be manufactured separately from the light guide body 48 and the main housing body 22 and inserted between these two components. Alternatively, it is conceivable to manufacture the internal sealing element 68 integrally with the light guide body 48. The base part 50 of the light guide body 48 separates a first sub-space 70, in which the light-emitting diode 40, the photodiode 42 and any other electrical / electronic components of the measuring assembly 38 are located, from second sub-spaces 72, 74, which are formed at least in the protrusions 32, 34 and each house one of the light guide fingers 52, 54, within the housing 20 of the sensor 10.The first sub-chamber 70 is sealed off from each of the second sub-chambers 72, 74 by the internal sealing element 68. Therefore, if wash water enters one of the second sub-chambers 72, 74, the internal sealing element 68 prevents the wash water from passing through into the first sub-chamber 70.

[0033] In an alternative embodiment, it is conceivable that the light guide fingers 52, 54 are not formed integrally on a common light guide body, but are separately manufactured components, with each of these components being sealed against the wall of one of the protrusions 32, 34 by a respective internal sealing element.

[0034] One can recognize in Fig. 1. The inner sealing element 68 is axially offset slightly away from the washroom 14 relative to the outer sealing element 66. This means that the inner sealing element 68 always obstructs any water ingress from the washroom 14 through one of the second sub-chambers 72, 74 into the first sub-chamber 70, and that no direct ingress of wash water from the washroom 14 into the first sub-chamber 70 is possible.

[0035] In other words, this relative axial position of the inner sealing element 68 to the outer sealing element 66 results in the first partial space 70 being limited solely by those wall sections of the housing 20 which, in the installation situation according to Fig. 1. Do not have contact with the wash water in washroom 14, i.e., they are free from a liquid environment.

[0036] It is understood that the main body of the housing 22 is sufficiently transparent at least in those areas where the light running along the light measuring distance 16 passes through its wall, whereby a certain milkiness of the material of the main body of the housing 22 is readily possible.

[0037] It is further understood that a tight connection between the base part 50 of the light guide body 48 and the main housing body 22 can also be achieved by crimping, welding, or bonding. In this case, an additional sealing element, such as the internal sealing element 68, is not required.

[0038] It has already been explained that the converging lens 60 causes a near-parallel alignment of the light beam emitted by the light-emitting diode 40 towards the converging lens 60. This parallelized light beam is then guided in the optical fiber 48 without significant change in divergence to the converging lens 62, where it is directed onto the photodiode 42. The cross-sectional shape of the light beam guided in the optical fiber 48 is, for example, circular, with the optical fiber fingers 52, 54 of the optical fiber 48 also having a circular cross-section. The diameter of the light beam guided in the optical fiber 48 can be, for example, at least 1 mm, at least 1.5 mm, or at least 2 mm. In one possible embodiment of the sensor 10, the diameter of this light beam can be, for example, approximately 2.4 mm.Assuming a circular bundle cross-section, this results in a bundle cross-sectional area of ​​approximately 4.5 mm. 2 Such a large cross-sectional area of ​​the light beam guided in the optical fiber 48 is advantageous for minimizing disturbances that may be caused by any particles or foam bubbles crossing the section 18 of the light measurement path 16. If such a particle floating in the wash water is, for example, a few tenths of a millimeter in size, it causes only a comparatively small attenuation of the output signal supplied by the sensor 10. In some cases, this can eliminate the need for time-based averaging of the sensor output signal to eliminate the influence of crossing particles or foam bubbles.

[0039] The parallelization of the light beam entering the optical element 48 by the converging lens 60 and the subsequent parallel guidance of this light beam within the optical element 48 up to the exit-side converging lens 62 ensure that a significant portion of the radiant energy emitted by the light-emitting diode 40 into the optical element 48 reaches the photodiode 42 and that the radiation losses along the light measurement path 16 are only comparatively small. For example, the radiant energy coupled out of the optical element 48 and reaching the photodiode 42 can exceed 70% of the radiant energy of the light beam emitted by the light-emitting diode 40 towards the converging lens 60, assuming the presence of air on the portion 18 of the light measurement path 16.

[0040] One can recognize in Fig. 1. Furthermore, both the light-emitting diode 40 and the photodiode 42 are arranged at a distance from the light guide body 48 and outside of it, i.e., they do not protrude – as in WO 2006 / 050767 A2, see e.g. there. Fig. 1 and Fig. 3 - into pockets of the light guide.

[0041] It will now be on Fig. 3. In the second embodiment shown there, identical or equivalent components as in the first embodiment are used with the same reference numerals as in the Fig. 1, Fig. 2 is designated, but with the addition of a lowercase letter. To avoid unnecessary repetition, reference is made to the preceding explanations regarding such identical or equivalent components, unless otherwise stated below.

[0042] In the sensor 10a according to the second embodiment, the interior of the housing 20a is not divided into sealed compartments. The light guide 48a has several laterally projecting support ribs 76a on its light guide fingers 52a, 54a, which serve to fix the light guide 48a in mounting grooves of the housing 20a (not shown in detail).

[0043] Furthermore, in Fig.3 The light beams running along the light measurement path 16a are shown as dashed lines. A divergent light beam 78a, directed from the light-emitting diode 40a towards the converging lens 60a, can be seen. This beam is transformed by the converging lens 60a into a parallel beam 80a. This parallel beam 80a travels in the light guide finger 52a to the reflection surface 56a. There, the parallel beam 80a undergoes total internal reflection and travels as a parallel light beam 82a through the measuring slit formed between the protrusions 32a, 34a of the housing 20a (corresponding to part 18a of the light measurement path 16a) until it reaches the reflection surface 58a. A further total internal reflection takes place there. The light travels from the reflective surface 58a as a parallel light beam 84a towards the converging lens 62a, where it is transformed into a convergent light beam 86a.

[0044] The refractive power of the converging lens 60a can be essentially the same as the refractive power of the converging lens 62a. It is understood, however, that the converging lenses 60a and 62a can alternatively have different refractive powers, depending, for example, on the directional characteristics of the light-emitting diode 40a and the photodiode 42a.

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