EP2710183A1

EP2710183A1 - Dryer having a moisture sensor and method for operating same

Info

Publication number: EP2710183A1
Application number: EP12719726.7A
Authority: EP
Inventors: Marcus Heyer-Wevers; Harald MOSCHÜTZ; Gudrun Schliecker; Thomas Schneider
Original assignee: BSH Bosch und Siemens Hausgeraete GmbH
Current assignee: BSH Hausgeraete GmbH
Priority date: 2011-05-20
Filing date: 2012-05-09
Publication date: 2014-03-26
Anticipated expiration: 2032-05-09
Also published as: WO2012159883A1; EP2710183B1; CN103547729A; DE102011076220A1; PL2710183T3; CN103547729B

Abstract

The invention relates to a dryer 1, comprising a drying chamber 2 for accommodating items of laundry 4, a moisture sensor 10, 11, 12, a control device 18 and a process air duct 5 in which a heating system 7 for heating the air and a blower 6 are situated, wherein at least one optical condensation sensor 10, 11, 12 is arranged outside the drying chamber 2 as the moisture sensor 10, 11, 12. The invention also relates to a method for operating said dryer.

Description

Dryer with humidity sensor and method for its operation

The invention relates to a dryer, comprising a drying chamber for receiving items of laundry, a humidity sensor, a control device and a process air duct, in which a heater for heating air and a fan are located, and a method for its operation.

In a tumble dryer (hereinafter abbreviated to "dryer"), wet laundry is dried by means of warm and dry process air The term "dryer" as used herein stands for dryers as such, but also for laundry dryers in which laundry is also used can be washed. Washer dryers are popular because they combine the functions of a washing machine and a tumble dryer in a space-saving device. In addition, a washer-dryer is already provided with a water connection, so that water is not only available for washing laundry, but also for further treatment of laundry items.

In a dryer, it makes sense that a drying process is carried out only up to a certain moisture content ("residual moisture") of the laundry items, because it can be detrimental to the further treatment of the laundry items if the drying is carried out too long and the laundry items contain less moisture as they do when stored under normal ambient conditions in a cabinet, they are very stiff and poorly folded or ironed, and for reasons of energy efficiency a drying process should only be carried out until a desired residual moisture of the dried laundry is achieved An additional drying process would lead to unnecessary energy consumption, since if the laundry is too dry it would be necessary to rewet the laundry during subsequent ironing.

It therefore makes sense to automatically terminate a drying process upon reaching a predetermined residual moisture content of the dried items of laundry. For this purpose, the moisture content of laundry items usually has to be measured by a suitable method. The determination of the moisture of the items of laundry can take place in various ways, for example by measuring electrical properties which are dependent on the moisture of the items of laundry, in particular the electrical conductivity of the items of laundry. For this purpose, two electrodes can be placed as moisture sensors in a drying chamber of the dryer, which is usually designed as a drum, that they contact the wet laundry items. An electrical voltage is then applied to the electrodes and the current intensity or the electrical conductance between the electrodes is measured. If the measured current intensity or the measured electrical conductance falls below a respectively predetermined threshold value, this can be concluded that a desired residual moisture level has been reached, so that a drying process can be ended.

Another known possibility is that, during a heating phase in a drying process, temperatures, amounts of heating energy and periods of time during which certain changes in such measurements result are measured and from such measurements a total time or amount of heating energy is determined for the drying process under the given conditions , For this purpose, the temperature of the process air is measured in particular at suitable locations in the process air duct, for example in front of and behind a heat exchanger, at which the moisture contained in the wet laundry items and carried with the moist, warm process air from the drying chamber condenses.

It is also known to measure the temperature of the process air flowing from the laundry items to be dried and to evaluate an increase in the temperature occurring in a late phase of the drying process; This increase results when the items of laundry are already largely dry, accordingly there is only little moisture to be evaporated in the items of laundry and thus the process air absorbs less moisture from the items of laundry. In a drying process, in which the moisture removed from the laundry items by means of the process air is condensed out in a condenser, a temperature difference across the condenser can also be measured for this purpose. Also from such a measurement can be concluded on the remaining low residual moisture of the dried laundry items and thus a total duration of the drying process, so that the drying process can be stopped at a predetermined residual moisture.

The known methods also make it possible to estimate the heat energy required for drying, in particular if the quantity of items to be dried can be clearly indicated.

DE 10 2006 053 274 A1 discloses a method for determining the charge amount of laundry in a cargo space with air outlet of a tumble dryer, wherein the absolute humidity in the air outlet from the cargo space is measured by means of a humidity sensor and the amount of charge in the cargo compartment by determining the maximum value and / or the course of the absolute humidity in the air outlet is determined from the hold. As soon as the amount of laundry and, if appropriate, other values such as the residual moisture are determined, the controller can stop the drying process with regard to time, air supply and possibly air temperature.

US 201 1/0041562 A1 describes a laundry treatment device having at least one sensor which is functionally coupled to the treatment chamber and which emits at least one signal which is indicative of the humidity inside the treatment chamber and which in the control for starting a moisture reduction device in accordance is used with a moisture reduction program. The internal humidity sensors can be located anywhere in the process air duct, e.g. be arranged in the treatment chamber, in the supply air pipe, in the Kindersicherheitsabzugsöffnung or in the exhaust pipe. Any type of sensor capable of determining relative or absolute humidity, such as infrared sensors, capacitive sensors, resistive sensors, and electrical conductivity sensors, can be used.

However, the sensors used in these methods have disadvantages. When using conductivity sensors, the sensor is not galvanically decoupled from the evaluating electronics, so that problems may arise due to possible coupling. Temperature sensors (eg NTC resistors), which protrude into the air flow whose temperature is to be measured, can be impaired in their function by adhering impurities (lint, lime, etc.). Besides that is in the aforementioned use of temperature sensors, an association between measured temperature values and a drying progress, for example the moisture content of the laundry, difficult.

A dryer, and in particular a washer-dryer, has surfaces on which moisture can precipitate on contact with moist, warm process air. It can thus come to a dewing of different surfaces associated with the moist, warm process air.

JP 5 184 791 A discloses a clothes dryer with a dew condensation apparatus, wherein a sensor for detecting condensation is arranged in a part of the exhaust pipe. In this case, the moisture is detected in the exhaust pipe by means of the sensor arranged in the exhaust pipe. The controller, when the value measured by the sensor exceeds a constant value, performs a dew condensation prevention operation for a certain time.

DE 10 2005 016 640 A1 describes a fiber-optic sensor device for detecting condensation and / or for temperature measurement with a light source, a light-emitting fiber connected to the light source, a light-receiving fiber and a light detector connected to the light-receiving fiber, and a light-emitting fiber and light-receiving fiber optically transparent sensor head. On the outer surface of the sensor head, a first and a second hollow curved interface are formed and arranged such that from the first hollow curved interface the light coupled via the light transmitting fiber into the sensor element is reflected onto the second hollow curved interface and reflected from the second hollow curved interface Light is coupled out into the light receiving fiber.

Against this background, the object of the invention was to provide a dryer and a method for its operation with which a drying method based on the determined residual moisture in laundry items can be better controlled. In particular, a point in time for the termination of a drying process should be able to be determined on the basis of the determined residual moisture content. The washer-dryer should preferably be easy to operate and have a simple construction. The object underlying the invention is achieved by a dryer and a method for its operation according to the respective independent claim. Preferred embodiments of the invention are listed in the respective dependent claims. Preferred embodiments of the dryer according to the invention correspond to preferred embodiments of the method according to the invention, even if it is not separately pointed out here in each case.

The invention thus relates to a dryer, comprising a drying chamber for receiving laundry items, a humidity sensor, a control device and a process air duct, in which there is a heater for heating air and a fan, wherein arranged as a humidity sensor outside the drying chamber at least one optical Betauungssensor is. Herein, "outside the drying chamber" means, in particular, a space, such as a container or a pipe, in which a wall of the space can come into contact with moist, warm process air and thereby be dewatered with moisture.

A dew point sensor is a sensor whose physical properties are due to the wetting of a surface of the sensor with a liquid, in particular an aqueous liquid, e.g. a condensation with water, change. The physical properties may include, for example, electrical or optical properties. In the latter case, it is an optical condensation sensor. In any case, it does not matter that a dew sensor actually measures the dew of any surface or the like, but that the dew sensor makes a measurement using condensation on its own surface or a certain portion thereof.

According to the invention, the at least one dewing sensor is an optical dewing sensor.

For the dryer according to the invention, it is particularly advantageous if it has points at which condensation of a condensation sensor can be measured particularly well. In a particularly preferred embodiment of the invention, the dryer is therefore designed as a washer-dryer with a tub in which a drum rotatably mounted in the tub is present as a drying chamber. In this case, it is particularly preferred that at least one condensation sensor is arranged in a suds tank wall. At least two Betauungssensoren are advantageously arranged in the tub wall.

In an embodiment of the invention in which a drying process can be controlled particularly well, a first dew sensor in a front tub wall, a second dew sensor in an upper tub wall and a third dew sensor in a back tub wall are arranged.

According to the invention, it is preferred that at least one condensation sensor is arranged above a rotational axis of the drum. The optical dewing sensor used in embodiments of the invention preferably has a first interface and a second interface, wherein the interfaces are formed and arranged relative to one another such that the light coupled into the dew sensor from a light-input fiber strikes the first interface and from there to the first interface second interface is reflected and the reflected light is coupled into a light-emitting fiber. Here, the light-introducing fiber and the light-exfoliating fiber, which generally comprise glass fibers, are generally connected to another outer surface (hereinafter referred to as "base surface") of the dew sensor, the light from the light-introducing fiber is preferably coupled perpendicularly to a base surface other than the interfaces the reflected light preferably decoupled perpendicular to the base surface.

The optical condensation sensor can also have very different shapes. Preferably, for example, when used in a washer-dryer, these molds are selected such that the at least one dewing sensor is flush with a tub wall. Then the risk of contamination of the sensor should be particularly low. The material used for the optical condensation sensor, as well as the shape and arrangement of the interfaces and the light introduction fiber and light extraction fiber, are preferably selected so that in the dew-free state the light coupled into the condensation sensor from the light introduction fiber is reflected to the light extraction fiber as far as possible without scattering losses and can be completely detected.

The condensation of an optical condensation sensor changes its optical properties. If a light-exposed interface of the optical condensation sensor is dewed, the coupled-in light is no longer completely reflected, but is partially refracted at the interface and emitted outward from the optical condensation sensor. As a result, the light intensity arriving at the light-deflecting fiber decreases, the decrease in intensity being a measure of condensation of the interface of the optical condensation sensor.

The optical condensation sensor generally comprises a sensor head, which is preferably made in one piece from a material such as glass or a plastic such as polycarbonate or polymethylmethacrylate. To the sensor head, the Lichteinleitungs- and light dissipation fiber, generally namable as optical fibers, connected. Preferably, the refractive indices of sensor head and optical waveguides are identical in this case. A suitable sensor head advantageously has a volume of 10 to 50 mm ³ and preferably of 20 to 40 mm ³ .

The refractive index of the material of the sensor generally depends on the material used, the wavelength of the light used and the temperature. Since the temperature changes in a dryer, a material is preferably selected for the optical condensation sensor whose refractive index is as little as possible dependent on the temperature.

Since the optical properties important for the operation of the optical condensation sensor depend on the temperature depending on the material used, it may be useful for precise measurements to take account of this temperature dependence and to deposit corresponding working curves in the control unit of the dryer. For temperature determination, for example, a temperature sensor generally also present in the dryer could be used. In a preferred embodiment of the invention, a relationship between a Betauungsgrad the Betauungssensors at a time t _s in a drying program and a duration t _prog the drying program is stored in the control device of the dryer. Here, the measurement of the time t and thus the reference point for the time t _s, for example, the turning on of the dryer and in particular the heater, but also the achievement of a predetermined temperature value.

In general, there is a more or less pronounced dependence of this relationship on the loading amount of the dryer with laundry items. The relationship between the degree of condensation of the dewing sensor and the duration t _per g of a drying program for different load quantities with laundry items is therefore preferably stored in the control device of the dryer.

The load of laundry items may be predetermined by a user of the dryer or measured automatically in a suitable manner in the dryer, for example, based on the weight increase of the drying chamber. For example, a user could manually enter the load on the dryer and thus supply the controller for further processing.

The control device is preferably designed such that a duration t _{prog of} a drying program can be determined, so that a drying program can be ended at a desired optimum time. However, it is also possible for the duration t _per g determined for a given drying program to be compared with a desired drying program duration t _set and then to be carried out by the control device to initiate a drying program enabling this desired drying program duration t _set . In particular, an initially preset drying program duration t _{set of} a given drying program can be changed accordingly. Preferably, in this case, the type and amount of laundry to be dried are taken into account. According to the invention, a washer dryer is preferably used as the dryer. In general, a washer-dryer has a heat exchanger in which the moisture contained in the moist warm air from the drying chamber can be condensed, the heat exchanger with cooling air, cooling water, or when using a heat pump with a refrigerant of the heat pump operated.

As used herein, "heating" refers to the air heating (process air) disposed in the process air duct 10. In addition, a laundry dryer generally also includes a heater for direct heating of an aqueous fluid, such as a wash liquor Heating called heating is generally located in the tub below the drum.

In general, a washer-dryer has a water supply system with which water can be passed through a generally existing dispenser tray from which detergent or laundry adjuvant portions can be added to the washer-dryer. In addition, a washer-dryer generally has a lye drainage system arranged on the bottom of the lye container with a drain pump and, in general, laundry hoppers and / or scooping devices. Preferably, a washer-dryer in the tub also contains a pressure sensor, which is preferably arranged in a lower region of the tub, so that the pressure of an aqueous liquid present in the tub can be measured.

The invention also relates to a method for operating a dryer, comprising a drying chamber for receiving items of laundry, a humidity sensor, a control device and a process air duct in which a heating for heating air and a fan are located, wherein as a moisture sensor outside the Drying chamber is disposed at least one optical Betauungssensor, comprising the steps

(a) heating air by operating the heater;

(b) introducing the heated air into the drying chamber;

(c) contacting the heated air with the at least one dewing sensor;

(d) measuring the condensation of the condensation sensor at at least one time t _s ;

(e) comparison of the condensation of the condensation sensor measured at time t _s with a relationship between one stored in the control device Betauungsgrad the Betauungssensors at a time t _s and a duration t, the drying program; and

(f) determining the duration t _per g of the drying program.

In a preferred embodiment of the method according to the invention for operating a dryer

(i) in a first drying phase, in which the Betauungsgrad the Betauungssensors with time increases, measured at time t _s1 condensation of the Betauungssensors with the stored for the first drying phase in the controller relationship between a Betauungsgrad the Betauungssensors at a time t _s and a duration t _pr0 g of the

Drying program and evaluated in terms of determining the duration tprog of the drying program; and or

(ii) in a second drying phase in which the dew point of the dewing sensor decreases over time, the condensation of the dewing _sensor measured at the time t _s2 > t _s1 with the relationship between a dewing degree of the dewing sensor stored for a second drying phase in the control device at a time t _s and a duration t _pr0 g of the drying program and evaluated with respect to a determination of the duration t _{prog of} the drying program.

Preferably, the duration t _{prog of} the drying program for different values of a residual moisture of the laundry items to be achieved is stored in the control _device . Preferably, a time t _{0 is} determined in the control device, at which the condensation of the condensation sensor has reached a predetermined condensation B ₀ , and the duration t _per g of the drying program is determined from the time t ₀ .

Preferably, the control device is designed such that a drying program is terminated after the time t _pr0 g. Alternatively, after determining the time t _pr0 g, a drying program can be configured and carried out such that a user-specified time period for a drying program is maintained. Particularly preferably, the dryer is designed as a washer-dryer with a tub in which a drum rotatably mounted in the tub is present as a drying chamber.

The invention has numerous advantages. In the dryer according to the invention and in the method for its operation, the drying process can be followed in a very efficient manner, so that a drying process can be automatically ended when a desired residual moisture content of the laundry items to be dried is reached. As a result, a desired drying result can be easily achieved in an energy-efficient manner. Moreover, for this purpose, the operation of the dryer according to the invention is relatively insensitive to contamination of the sensor, since the sensor can be easily calibrated before each drying process. This is particularly good because the dew sensor is an optical dew point sensor. Moreover, the invention works particularly well when the dryer is designed as a washer-dryer, in particular when in embodiments of the invention, at least one Betauungssensor is integrated into a suds container wall.

The invention will be further explained below with reference to an exemplary dryer shown in the attached drawing. The dryer is designed here as a washer-dryer. Other embodiments than those illustrated are conceivable.

The washer-dryer 1 shown in the figure as a dryer has a lye container 3 with a front lye container wall 15, an upper lye container wall 16 and a rear lye container wall 17. In the tub 3 a about a substantially horizontal axis 27 rotatably mounted drum 2 is arranged as a drying chamber in which are to be dried laundry items 4. In the front tub wall 15 is a front Betauungssensor 10, in the upper tub wall 16 is an upper Betauungssensor 1 1 and in the rear tub wall 17, a rear Betauungssensor 12 is arranged. These are optical condensation sensors. The optical condensation sensors 10, 1 1 and 12 are located in an upper part of the tub 3, ie above the substantially horizontally arranged axis of rotation 27. The Betauungssensoren 10, 1 1 and 12 are each about optical fibers 30 with a control unit 26 for the Betauungssensoren which communicates with a controller 18 of the dryer, connected. In this case, an optical fiber 30, not shown here in detail, comprises two fibers, a light-guiding fiber for the light transmitted to the respective condensation sensor, and a light-deflecting fiber for the light derived from the respective condensation sensor. For each dew sensor, the difference in the generally wavelength-dependent intensity between incoming and outgoing light is a measure of the dew of the optical dew sensor 10, 11, 12.

The tub 3 is otherwise connected via a lye drain line 19 to a drain pump 14 containing an aqueous liquid 28, e.g. in the drying accumulating condensate can dispose of the tub 3 via a sewer line 13 to the outside of the washer dryer. The drum 2 is driven by means of a drive motor 29.

The drum 2 is loaded through a filling opening 22 with laundry items 4 to be dried. In order to be able to wash 1 items of laundry in the washer-dryer, the washer-dryer 1 is connected via a water supply system 20 to an external water supply not shown here. The water supply system 20 is connected via a valve 9 with a dispenser 21, from which with the aid of water from the water supply system 20 detergent or Waschhilfsmittelportionen can be transported into the tub 3. In the present case, this takes place via a part of a process air channel 5 and a sleeve 23.

For drying wet laundry in the drum 2, in the washer-dryer 1 of the figure, which operates on the recirculation principle, the air heated by means of a heater 7 ("process air") is conveyed through a fan 6 in a process air duct 5. Dry dry warmed occurs here After passage through the drum 2 and drying of moist laundry items 4 located in this then the moist warm process air 31 passes through a rear outlet 24 from the tub 3. In the here In the embodiment shown, the moist, warm process air 31 reaches a heat exchanger 8, where the moisture contained in it condense due to the cooling of the process air and can be collected in a condensate container (not shown here) Alternatively, the condensate can flow into the tub 3, from where it flows over the Laugenablaufleitung 19 using the drain pump 14 via the wastewater line 13 to the outside of the washer-dryer can be taken care of. In the embodiment shown here, the condensate 28 is then pumped out of the tub 3 via the lye drain line 19 by means of the sewage pump 14. In the figure, the small arrow indicates the flow direction of the condensate. The dehumidified process air then continues to flow in the process air duct 5 and can be heated again by means of the heater 7 and enter the drum 2 as a warm, dry process air 25 via the sleeve 23, etc.

To carry out the method according to the invention, air is first heated with the heater 7 and the heated dry air 25 is introduced into the drum 2. Subsequently, the moist warm air 31 from the drum 2 with the Betauungssensoren 10, 1 1, 12 brought into contact and measured the condensation of the sensors at time t _s . Subsequently, the condensation of the dewing sensor 10, 11, 12 measured at the instant t _{s is} compared with a relationship between a degree of condensation of the dewing sensor 10, 11, 12 at a time t _s and a duration tpr _o g of the drying program stored in the control device 18 and the duration t _per g of the drying program determined. In this case, preferably two variants of the method are used ((i) or (ii)), which can also be used in combination: (i) in a first drying phase, in which the degree of condensation of the

The condensation rate of the condensation sensor 10, 1, 12 measured at the time t _s1 with the relationship between a condensation degree of the condensation sensor 10, 1 1 stored in the control device 18 for the first drying phase, 12 compared to a time t _s and a duration t _pr0 g of the drying program and evaluated with respect to a determination of the duration t _pr0 g of the drying program.

(ii) In a second drying phase, in which the degree of condensation of the

Betauungssensors 10, 1 1, 12 decreases with time, the measured at the time t _s2 > t _s1 condensation of the Betauungssensors 10, 1 1, 12 with that for the second

Drying phase in the control device 18 deposited relationship between a Betauungssensor the Betauungssensors 10, 1 1, 12 at a time t _s and a duration t _per g of the drying program compared and in _Evaluated for a determination of the duration t _pr0 g of the drying program.

In particular, a time t _{0 is} determined in the control device 18, at which the condensation of the Betauungssensors 10, 1 1, 12 or a selected one of the plurality of Betauungssensoren 10,1 1, 12 has reached a predetermined condensation B ₀ , and is the duration t _prog the drying program determined from the time t ₀ .

In these methods, the fact can be exploited that due to the flow direction of the moist, warm process air, the individual Betauungssensoren can be dewetted differently. In this case, the dewing sensors 10, 11 and 12 are gradually dewatered with water in a first drying phase (generally the heating phase). If, in this first phase, the condensation is measured at two different points in time, there is a temporal increase in condensation. In the later course of the drying process, the dewing of the dewing sensors will generally decrease in a second drying phase. As a rule, first the dew at the front dew point sensor, then at the upper dew point sensor and finally at the rear dew point sensor will decrease.

The process air is circulated until a desired degree of drying, ie residual moisture content of the laundry items, is reached. Then, the drying process caused by the controller is ended.

LIST OF REFERENCE NUMBERS

1 washer-dryer

2 drum

3 tubs

4 pieces of laundry

5 process air circulation

6 blowers

7 heating, air heating

8 heat exchangers

9 water valve

10 front condensation sensor

1 1 upper condensation sensor

12 rear condensation sensor

13 sewer pipe

14 sewage pump

15 front tub wall

16 upper tub wall

17 rear tub wall

18 control device

19 Lye drain line

20 water supply system

21 induction bowl

22 filling opening

23 cuff

24 rear exit (from the tub)

25 Dry, warm process air

26 Control unit for condensation sensors

27 axis of rotation of the drum

28 aqueous liquid, e.g. condensate

29 drive motor

30 optical fiber (s) (optical fiber)

31 moist, warm process air

Claims

1. dryer (1), comprising a drying chamber (2) for receiving laundry items (4), a humidity sensor (10, 1 1, 12), a control device (18) and a process air channel (5), in which a heating ( 7) for heating air and a fan (6) are located, characterized in that as the humidity sensor (10, 1 1, 12) outside the drying chamber (2) at least one optical Betauungssensor (10, 1 1, 12) is arranged.

2. dryer (1) according to claim 1, characterized in that the dryer (1) as a washer-dryer with a tub (3) is configured in which a drying chamber (2) in the tub (3) rotatably mounted drum (2) is.

3. dryer (1) according to claim 2, characterized in that at least one Betauungssensor (10, 1 1, 12) in a lye container wall (15,16, 17) is arranged.

4. dryer (1) according to claim 3, characterized in that in the tub wall (15, 16, 17) at least two Betauungssensoren (10.1 1, 12) are arranged.

5. dryer (1) according to claim 4, characterized in that a first Betauungssensor (10) in a front tub wall (15), a second Betauungssensor (1 1) in an upper tub wall (16) and a third Betauungssensor (12) in a rear suds container wall (17) are arranged.

6. dryer (1) according to one of claims 1 to 5, characterized in that at least one Betauungssensor (10, 1 1, 12) above a rotational axis (27) of the drum (2) is arranged.

7. dryer (1) according to claim 1, characterized in that the optical Betauungssensor (10, 1 1, 12) has a first interface and a second interface, wherein the interfaces are formed and arranged to each other, that of a light introduction fiber (30) into the dew sensor (10, 11, 12) coupled light impinges on the first interface and is reflected by this on the second interface and the reflected light is coupled into a light extraction fiber (30).

8. Dryer according to one of claims 2 to 7, characterized in that the at least one Betauungssensor (10, 1 1, 12) with a lye container wall (15, 16, 17) is arranged flush.

9. dryer (1) according to one of claims 1 to 8, characterized in that in the control device (18) has a relationship between a Betauungsgrad the Betauungssensors (10, 1 1, 12) at a time t _s in a drying program and a duration t _Proog the drying program is deposited.

10. dryer (1) according to claim 9, characterized in that the relationship between Betauungsgrad and the duration t _{prog of} the drying program for different loading amounts with laundry items (4) is deposited.

1 1. Dryer (1) according to any one of the preceding claims, characterized in that the dryer (1) as a washer-dryer (1) with a tub (3) is configured in which a drying chamber (2) in the tub (3) rotatable mounted drum (2) is present.

12. A method for operating a dryer (1), comprising a drying chamber (2) for receiving laundry items (4), a humidity sensor (10, 1 1, 12), a control device (18) and a process air duct (5), in the there are a heater (7) for heating air and a fan (6), wherein outside the Drying chamber (2) at least one optical Betauungssensor (10, 1 1, 12) is arranged, comprising the steps

(a) heating air by operation of the heater (7);

(b) introducing the heated air into the drying chamber (2);

(c) bringing the heated air into contact with the at least one dewing sensor (10, 11, 12)

(d) measuring the dewing of the condensation sensor (10, 11, 12) at at least one time t _s ;

(e) comparison of the condensation of the condensation sensor (10, 11, 12) measured at the time t _s with a relationship between a condensation level of the condensation sensor (10, 11, 12) stored in the control device (18) at a time t _s and a duration t _{prog of} the drying program; and

(f) determining the duration t _pr0 g of the drying program.

13. A method for operating a dryer (2) according to claim 12, characterized in that

(i) in a first drying phase in which the Betauungsgraddens the Betauungssensors (10, 1 1, 12) increases over time, the measured at time t _s1 condensation of the Betauungssensors (10, 1 1, 12) with that for the first drying phase in the control device (18) stored relationship between a Betauungsgrad the Betauungssensors (10,1 1, 12) at a time t _s and a duration t _{prog of} the drying program is compared and evaluated in terms of determining the duration t _prog the drying program; and or

(ii) in a second drying phase, in which the Betauungsgrad of the dew sensor (10, 1 1, 12) decreases with time, the time t _s2> t _s1 measured condensation of dew sensor (10, 1 1, 12) to the for the second drying phase in the control device (18) stored relationship between a Betauungsgrad the Betauungssensors (10, 1 1, 12) at a time t _s and a duration t _{prog of} the drying program compared and evaluated with respect to a determination of the duration t _{prog of} the drying program becomes. A method according to claim 12 or 13, characterized in that in the control device (18) the duration t _per g of the drying program for different values of a residual moisture of the laundry items (4) to be achieved is stored.

Method according to one of claims 12 to 14, characterized in that in the control device (18) a time t _{0 is} determined, to which the condensation of the Betauungssensors (10, 1 1, 12) has reached a predetermined condensation B ₀ , and the Duration t _prog the drying program from the time t _{0 is} determined.