EP1344487B1 - Device and method for optically sensing the dryness degree in a house appliance - Google Patents

Description

The invention relates to a device and a method in a household appliance, in particular a dishwasher, with a humidity sensor for detecting the degree of dryness within a container or air duct of the household appliance.

In a conventional dishwashing machine, the rinsing liquid is pumped off after the last rinse and the heating of the dishwasher is switched on for a fixed period of time. By heating the atmosphere in the dishwasher container stored therein items is heated so that it gives off increased moisture during the dry phase. The humidity condenses on the cooler inner walls of the washing container and eventually runs off to the dishwasher sump. In this case, the duration of heating is determined independently of the loading of the dishwasher and thus leads to an inefficient drying process, in which sometimes unnecessary heating energy is consumed.

Domestic appliances, which according to the preamble of claim 1 have moisture sensors are out US 3,116,982 and US 3,870,417 known.

It is therefore an object of the invention to control a dry phase in a household appliance as needed, so that heating energy is saved.

This object is achieved with the features of claim 1 (device) and the Ansprüchs 10 (method).

According to claim 1, the household appliance has a humidity sensor for detecting the degree of dryness within a container or air duct. The humidity sensor detects the humidity of the atmosphere either directly within the container or in an air duct, which is in communication with the container. Through the air duct, for example, during the dry phase, the air circulates out of the container and the air moisture transported through the air duct is separated by means of a condensation device or discharged from the domestic appliance. The humidity sensor detects the moisture adhering to it from a defined detection surface in the interior of the container or the air duct. During the heating and / or drying phase, the humidity from the container interior of the household appliance is reflected at the detection surface in the form of condensation droplets or a moisture film. By detecting the moisture on the detection surface is determined whether the dry phase has progressed so far that the humidity from the container interior is already largely removed.

With decreasing humidity, the detection surface also dries, so that in the absence of the moisture film or the drops on the detection surface on the end of the drying phase can be closed. This can be switched off at a reproducible degree of humidity in the container, the drying heater and possibly a circulating air blower. If, for example, a large number of items to be washed is disposed of in a dishwashing machine, this releases moisture to the dishwashing atmosphere for a longer period of time The moisture adheres to the detection surface for longer. Therefore, a longer drying phase is carried out until complete drying of the dishes. Few items to be washed accordingly less moisture to the Spülraumatmosphäre from and the moisture on the detection surface dries faster, so that based on the moisture detection, the drying phase is turned off earlier. The same applies, for example, to a tumble dryer depending on the loading state or the residual moisture of the laundry to be dried.

The detection surface is an inner surface of a defined wall portion of the container or the air channel, so no additional area within the household appliance for moisture detection must be provided. The defined wall region is a plate element, which is arranged in or on an opening of the container or channel wall. Thus, the inner dimensions and inner contours of the container or the air duct for measuring the humidity are not changed substantially, so that they retain their full functionality unchanged. According to an advantageous embodiment, the plate element is connected by means of welding, thermal welding, gluing or by means of a sealing sleeve with the adjacent container or channel wall. This results in a tight and easy to install connection between the container or channel wall and the plate member.

Since the plate member is a glass sheet or a transparent plastic sheet, optical detection of the moisture on the detection surface is enabled. Depending on the optical wavelength during measurement is the plate element in the visible range, in the UV range or in the infrared range permeable.

In a particularly advantageous embodiment of the detection surface is assigned a condensation device. As long as there is humidity in the atmosphere of the container, the condenser accelerates the condensation of moisture on the detection surface by cooling it. As a result, the detection surface is colder than the surrounding surface inside the container or the air duct and the existing humidity is reliably detected by the condensation. In an advantageous embodiment, the detection surface is in thermal contact with a Peltier element. The Peltier element is operated during the dry phase and extracts heat from the detection surface. In a further embodiment, the detection surface communicates with a condensation device which is present anyway for accelerating the drying, for example a water container or a condensation dryer. By such a condensation device, the drying process is accelerated while removing heat of the detection surface.

By optically detecting the moisture adhering to the sensing surface, a wear-free, non-contact sensing sensor is provided. Especially in the case where the humidity sensor is disposed outside the atmosphere containing atmospheric moisture, the sensor is subject to a low thermal and chemical stress. In a dishwasher, the sensor is advantageously arranged and operated outside of the aggressive Spülraumatmosphäre.

Advantageously, the humidity sensor on a light sensor which detects a caused by the adhering moisture change in the lighting conditions. If no external light source (for example ambient light) is available in a container which is enclosed on all sides, the light to be detected by the light sensor is advantageously generated by a light source. In a particularly advantageous embodiment, the light source and the light sensor are arranged at a distance from one another, wherein the light emitted by the light source passes to the light sensor after the reflection on the surface of the detection surface. In the presence / absence of a moisture film or drops on the detection surface, the reflection on the surface of the detection surface changes such that the intensity of the reflected light changes due to the humidity and this change is evaluable as the presence / absence of moisture. Depending on the refractive index of the sensing surface, the refractive index of air and the refractive index of the moisture, a total reflection is achieved in the dry phase, in which maximum intensity occurs on the light sensor, while in the presence of a moisture film, the intensity is reduced by reflection losses , Or the total reflection is achieved conversely in the presence of moisture and in the absence of moisture, the intensity is attenuated by reflection losses.

Regardless of whether in the device described above, it totally reflects the incident light of the light source in the wet or dry condensation surface of the humidity sensor, at least one reference value for the Set and save maximum light intensity. This may be done at the factory or during operation of the dishwasher at appropriate times and at various intervals. The reference value of the intensity maximum is required in order to be able to calculate the reflection losses from the measured light intensities during the process and to draw conclusions for the required heating demand. In order to ensure that the existing moist hot air allows safe conclusions about the degree of dryness within the container, it is advantageous to cool the detection surface of the humidity sensor. By this measure is achieved that existing moist hot air is reflected on this case in any case and if the detection area is colder than the environment, it is also assumed that this dries last and thus the time at which in each point of the container interior a desired Drying degree is achieved, can be determined safely. The formation of condensation on the detection surface of the humidity sensor is a necessary prerequisite in order to obtain measured values of the detected light intensities corresponding to the degree of drying of the container interior. The time course of the drying process is dependent on a variety of parameters, such as the loading amount and the material of the set items, since they are not influenced, it makes sense to continuously detect the emitted and reflected at the detection surface of the humidity sensor light intensities. The measured values of the light intensities are transmitted to a control unit and evaluated there according to predetermined algorithms. In order to be able to conclude on the required heating requirement until complete drying of the dishes, various evaluation methods are applicable, for example, a table be deposited, the average values of light intensity minimum residual maturity assigns the heating and / or heating demand, on the other hand, the drying process can be determined from the rate of change of the light intensities. Furthermore, a combination of different evaluation methods is conceivable, the other parameters used during dishwasher operation. Depending on the selected evaluation method of the measurement results, it may be useful in terms of minimizing the heating demand, the heating continuously or clocked on and / or off. If, for example, the contiguously incoming measured values of the light intensity are averaged and recourse is made to a stored remaining running time of the heating, then it may be expedient to switch off the heating only after the remaining heating time has expired, if the measured light intensities after expiry of the predefined residual running time lie within a tolerance interval of the heating time There is a clocked operation of the heater is driven, which is clocked in terms of its duration and its performance, so that in phases of low or no heating power, it is possible to compare the measured values of light intensity with its predetermined reference value, so a appropriate time to shut down the heater to determine.

• Fig. 1 einen schematischen Querschnitt durch eine Geschirrspülmaschine mit optischen Feuchtesensoren,
• Fig. 2 eine Detailansicht eines der optischen Feuchtesensoren,
• Fig. 3a die Reflektionsverhältnisse eines Lichtstrahls ohne Feuchtigkeit auf der Sensorfläche und
• Fig. 3b die Reflektionsverhältnisse bei Feuchtigkeit auf der Sensorfläche.

With reference to figures embodiments of the invention will be explained in more detail. Show it:

• Fig. 1 a schematic cross section through a dishwasher with optical humidity sensors,
• Fig. 2 a detailed view of one of the optical humidity sensors,
• Fig. 3a the reflection ratios of a light beam without moisture on the sensor surface and
• Fig. 3b the reflection conditions with moisture on the sensor surface.

Fig. 1 2 shows a schematic cross-sectional view of a washing container 1 of a dishwasher and an adjacent circulating air channel 2. In the washing container 1, an upper dish rack 3, an upper spraying arm 4, a lower dish rack 5 and a lower spraying arm 6 are arranged in a manner known per se. During the drying phase for drying the dishes placed in the dishwashing baskets 3, 5, the dishwashing atmosphere containing moisture is sucked out of the washing container by a fan 7 in the lower washing compartment area into the air duct 2 and discharged from the latter into the washing compartment 1 in the upper washing compartment area. At the air duct 2, a water tank 8 is arranged, which extracts heat from the warm Spülraumatmosphäre, whereby moisture is reflected on the container wall. In this case, the container wall acting as a condensation surface is formed as a side wall of the air channel 2.

A first humidity sensor 10 is arranged at an opening 11 in the lower region of the washing container 1. The first humidity sensor 10 comprises a glass plate 12 which rests on the opening 11, and a measuring head 13, which is arranged on the glass plate 12 on the side facing away from the Spülbehälterinneren.

Fig. 2 shows a detailed view of the first humidity sensor 10. The glass plate 12 is at its edge region with a elastic adhesive (not shown) adhered to an adjacent to the opening 11 inner wall 14 of the washing container 1. The elastic adhesive compensates for stresses due to temperature changes during operation of the dishwasher between the glass plate 12 and the inner wall 14. The measuring head 13 is formed in two parts from a Peltier element 15 and a detector element 16. In another embodiment, not shown here, the Peltier element 15 may also be integrated directly into the detector element 16, so that the measuring head 13 is integrally formed. The Peltier element 15 and the detector element 16 are connected via a combined measuring and control line 17 with an in Fig. 1 shown control unit 18 connected to the signal evaluation. The Peltier element 15 cools the area adjacent to the detector element 16 surface of the glass plate 12 and thereby preferably supports the condensation on the glass plate 12. The moisture on the glass plate 12 evaporates only when almost all the humidity is removed from the rinsing atmosphere in the washing compartment 1 ,

Fig. 3a shows a detailed view of the detector element 16. In a common housing of the detector element 16, a light-emitting diode 20 and a photodiode 21 are arranged. The wavelength or the wavelength band of the light emitting diode 20 and the photodiode 21 are matched to each other, so that the photodiode 21 at the wavelength or the wavelength band of the light emitting diode 20 provides maximum output power. To avoid scattered light incident on the photodiode 21 of the light emitting diode 20, a partition 22 is provided within the housing. The light emitting diode 20 and the photodiode 21 are aligned with each other so that the collimated light beam from the photodiode 20 into the glass plate 12 penetrates, where it is reflected on the detector element 16 opposite surface of the glass plate 12, exiting the glass plate 12 and reaches the photosensitive surface of the photodiode 21. In a further embodiment, to avoid reflection losses, a transparent matching layer between the exit side of the light-emitting diode 20 and the surface of the glass plate 12 and between the. Surface of the glass plate 12 and the entrance side of the photodiode 21 are provided.

The angle α between the light beam within the glass plate 12 and the surface of the glass plate is chosen so that when dry surface of the glass plate 12 total reflection occurs. In this case, the entire intensity is reflected on the washing container 1 facing surface of the glass plate 12 and deflected in the direction of photodiode 21. Fig. 3b shows the course of the light beam of the arrangement of Fig. 3a when moisture is on the surface of the glass plate 12. Instead of the refractive index transition glass plate / air is now a refractive index transition between the glass plate and water before. In this case, no total reflection occurs more and part of the light beam from the light emitting diode 20 is transmitted at the border crossing glass / water through the water droplets 23 out of the glass plate. The reflected intensity of the light beam to the photodiode 21 is attenuated, so that the presence of water droplets 23 and a moisture film on the inner surface of the glass plate 12 is detected via the light intensity attenuation.

In the formation of individual drops of water on the glass plate 12 instead of a water film is not for everyone Point on the glass plate ensures that a transition glass / water is present. To compensate for this statistical fluctuation, in other, not shown embodiments, either the light beam from the light emitting diode 20 is radiated at a wide angle and detected via a correspondingly large photosensitive area of the photodiode 21 or a plurality of spatially distributed photodiodes. It can also be provided several light emitting diodes / photodiode pairs. Thus, the presence of moisture is detected over a larger spatial area or over several points of the glass plate, so that even when dropping the moisture is reliably detected.

Fig. 1 shows yet a second embodiment of the arrangement of a humidity sensor. In this case, a second humidity sensor 30 is arranged in a moisture-sealed housing in the interior of the water tank 8. The measuring head 31 of the second humidity sensor 30 is seated on the plastic wall of the water tank 8, which is part of the partition wall between the water tank 8 and air duct 2. The plastic wall 32 is optically transparent to the wavelength which is emitted by a light-emitting diode 20 of the measuring head 31. The inner structure of the measuring head 31 corresponds to that of the detector element 16. In the second humidity sensor 30 is compared to the in Fig. 3a and 3b shown arrangement, only the glass plate 12 replaced by the plastic wall 32. The second humidity sensor 30 is connected via a measuring and control line 33 to the control unit 18. Optionally, the dishwasher has only the first humidity sensor 10, only the second humidity sensor 30 or both humidity sensors 10, 30.

At the beginning of the drying phase, the moisture measurement is activated by means of the first and / or second humidity sensor. Possibly. the measurement is started only delayed, so that after the start of the dry phase, ie the heating of the dishwasher interior, a condensate can form on the measuring surface. During drying, the moisture is continuously monitored in the form of a moisture film or drop. After the moisture is largely removed from the purge atmosphere, the moisture on the sensor surface begins to evaporate and the intensity of the reflected light beam changes. This change is detected by the photodiode 21 and evaluated by the control device 18. After the decrease of the humidity has been detected, the heater and / or the fan 7 is turned off and the drying process is ended. Optionally, after the detection of the drying or the humidification reduction, the fan 7 can still run for a predefined period of time.

LIST OF REFERENCE NUMBERS

• 1: washing container
• 2: air duct
• 3: upper dish rack
• 4: upper spray arm
• 5: lower crockery basket
• 6: lower spray arm
• 7: Blower
• 8: water tank
• 10 first humidity sensor
• 11: opening
• 12: glass plate
• 13: measuring head
• 14: inner wall
• 15: Peltier element
• 16: Detector element
• 17: Measuring and control line
• 18: Control unit
• 20: LED
• 21: photodiode
• 22: partition
• 23: drops of water
• 30: second humidity sensor
• 31: measuring head
• 32: plastic wall
• 33: Measuring and control line

Claims (11)

1. Domestic appliance, in particular dishwasher, having a dampness sensor (10, 30) for detecting the degree of dryness within a container (1) or air channel (2) of the domestic appliance, wherein the dampness sensor (10, 30) detects moisture (23) adhering to a detection surface (12, 32) in the interior of the container (1) or of the air channel (2), characterised in that the detection surface (12, 32) is an inner surface of a glass panel or transparent plastic plate arranged in or on an opening (11) of the container wall or channel wall (14), and which is permeable as a function of the optical wavelength when measuring in the visible range, in the UV range or in the infrared range and optical detection of the air moisture from the container interior, which is precipitated at the detection surface during a heating and/or drying phase, is facilitated.
2. Domestic appliance according to claim 1, characterised in that the glass or plastic plate is joined to the adjoining container wall or channel wall (14) by means of sealing, thermo-sealing, adhesion or a sealing sleeve.
3. Domestic appliance according to one of the preceding claims, characterised in that a condensation device (15, 8) is assigned to the detection surface (12, 32).
4. Domestic appliance according to claim 3, characterised in that the condensation device (15) has a Peltier element which is thermal contact with the detection surface (12) and which withdraws heat from the detection surface (12), or a water container which is in thermal contact with the detection surface (32) or the condensation device is designed as a condensation dryer.
5. Domestic appliance according to claim 1, characterised in that the dampness sensor (10, 30) has at least one light sensor (21), in particular at least one photodiode.
6. Domestic appliance according to claim 5, characterised in that the dampness sensor (10, 30) has at least one light source (20), in particular at least one light-emitting diode.
7. Domestic appliance according to claim 6, characterised in that the light sensor (21) responds to the light emitted by the light source (20).
8. Domestic appliance according to claim 7, characterised in that the light from the light source (20) is reflected at least once at a surface of the detection surface (12, 32) before it reaches the light sensor (21).
9. Domestic appliance according to claim 8, characterised in that the light from the light source (20) is reflected at such an angle to the surface of the detection surface (12, 32) that when the surface is dry, total reflection of the light occurs and when there is moisture on the surface, at least a part of the light is burst forth from the light path to the light sensor (21), or that when there is moisture on the surface, total reflection of the light occurs and when the surface is dry, at least a part of the light is burst forth from the light path to the light sensor (21).
10. Method for determining the degree of dryness within a container (1) or air channel (2) in a domestic appliance, in particular a dishwasher, by means of at least one dampness sensor (10, 30), which optically detects moisture (23) adhering to a detection surface (12, 32) in the interior of the container (1) or of the air channel (2), characterised by the method steps

    - determination and storage of at least one reference value of the intensity of the light emitted by a light source (20), and which is reflected at the dry detection surface (12, 32) of the dampness sensor (10, 30) before it reaches a light sensor (21), wherein the detection surface (12, 32) is an inner surface of a glass panel or transparent plastic plate arranged in or on an opening (11) of the container wall or channel wall (14), and which is permeable as a function of the optical wavelength when measuring in the visible range, in the UV range or in the infrared range,

    - cooling of the detection surface (12, 32) of the dampness sensors (10, 30) and precipitation of the moist-hot air associated therewith on the detection surface (12, 32),

    - continuous detection of the intensity of the light emitted from the light source (20) by the light sensor (21), wherein the light of the light source (20) is reflected at the detection surface (12, 32) of the dampness sensor (10, 30) before it reaches the light sensor (21),

    - transfer of the values of the measured light intensities of a detector element (16) via a measuring and control line (17) to a control unit (18).
11. Method according to claim 10, characterised by at least one of the method steps

    - evaluation of the measured results of light intensity and ascertaining of the heat requirement resulting therefrom until complete drying of dishes.

    - Controlled continuous or clocked connection and/or disconnection of a heating by the control unit (18).

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