EP3268529B1 - Method for operating a washing machine having an electrochemical sensor and washing machine suitable therefor - Google Patents

Description

The invention relates to a method for operating a washing machine with an electrochemical sensor and a washing machine suitable for this purpose. The invention relates in particular to a method for operating a washing machine with a container, a drum for holding items of laundry, a drive motor for the drum, an electrochemical sensor in the container for determining an electrochemical signal depending on a composition of an aqueous liquid in the container, and a Control device, as well as a washing machine suitable for carrying out this method.

In a washing machine, laundry is generally treated in a washing phase for cleaning with a washing solution containing detergent. After a rinsing phase with water, in which the suds and/or dirt in or on the laundry are removed, the laundry is often treated with a fabric softener. For cost and environmental reasons, it makes sense that an optimal amount of laundry treatment agent (especially detergent and fabric softener) is used. Overdosing or underdosing should be avoided. In particular, incorrect dosing of the detergent can result in foaming (overdosing) or poor washing performance (underdosing). To ensure that this does not happen, it is desirable to monitor and optimally adjust the detergent concentration.

A washing machine has therefore been proposed which can determine an optimal amount of detergent, for example, and can give a user of the washing machine a dosage recommendation on a display with an exact indication of the amount of detergent, for example, to be used.

The WO 03/029550 A1 describes a process-controlled household appliance with a microcomputer and a display for texts, which also includes a display field for the Display of the amount of additives (e.g. detergent) that is expected to be required in a work process (e.g. a washing program). The household appliance has a device through which, for example, additives can be added to a washing process, the dosage of which must be carried out by an operator.

To save detergent, it makes sense to dose the amount of detergent depending on the type and level of soiling on the laundry items to be washed. A detergent dosage that is optimally tailored to a batch of laundry items not only saves energy and water, but also reduces wastewater pollution.

The DE 29 17 859 describes a method for monitoring and controlling the program, in particular the water supply and/or the addition of cleaning or rinsing agent in automatic washing and dishwasher machines, with sensors responding to the surface tension and/or the water hardness and/or the electrical conductivity of the washing liquid in the Machine are provided, which intervene in the program flow via an electrical control circuit and control the water filling quantity, the water changes and / or the dosage of the cleaning or detergent addition.

The EP 2 533 035 A1 describes a device for detecting material properties of a medium, with a measuring device including a sensor device that is connected to the medium, and a control device for controlling the sensor device with signals of a predetermined frequency range, and a control device for controlling the operation of the measuring device and specifying the predetermined frequency range, wherein the control device is provided for determining the course of the impedance Z of the medium corresponding to the predetermined frequency range as a function of the frequency, and for outputting a detection signal, and the control device is provided for evaluating the detection signal of the control device, determining a plurality of characteristic Points (P1 to P4) of the course of the impedance Z and generation of a result signal regarding the properties of the Mediums. This should make it possible, for example, to determine whether a washing solution requires further addition of washing agent.

• Zuführen einer Teilmenge eines Waschmittels zu der Wassermenge zur Bildung einer Waschlauge (Schritt 1),
• Erfassen eines Betrags Z und eines Phasenwinkels ϕ einer Impedanz der Waschlauge für eine vorbestimmte Anzahl von Frequenzen von Ansteuerungssignalen und Erzeugen einer entsprechenden Anzahl jeweiliger Messwerte (Schritt 2),
• Ermitteln einer Steigung aus jedem Messwert des Phasenwinkels (Schritt 3),
• Berechnen eines jeweiligen Mittelwertes aus der Anzahl der Steigungen und den Beträgen der Impedanz (Schritt 4),
• Ermitteln eines Bestimmungsproduktes MBP aus dem Mittelwert der Steigungen und dem Mittelwert der Beträge der Impedanzen (Schritt 5B),
• Vergleichen des Bestimmungsproduktes mit einem vorbestimmten Schwellenwert (Schritt 6B), und
• Wiederholen der Schritte 1 bis 6B, bis das Bestimmungsprodukt gleich oder größer als der Schwellenwert (XB) ist (Schritt 7).

The EP 2 767 825 A1 describes a method and a device for determining a micelle formation concentration. The method is carried out in a washing device which has an amount of water required to carry out a washing process, with the following steps

• adding a portion of a detergent to the amount of water to form a wash liquor (step 1),
• Detecting an amount Z and a phase angle ϕ of an impedance of the washing liquor for a predetermined number of frequencies of control signals and generating a corresponding number of respective measured values (step 2),
• Determining a slope from each phase angle measurement (step 3),
• Calculating a respective mean value from the number of slopes and the amounts of the impedance (step 4),
• Determining a determination product MBP from the average of the slopes and the average of the amounts of the impedances (step 5B),
• comparing the determination product with a predetermined threshold (step 6B), and
• Repeat steps 1 to 6B until the determination product is equal to or greater than the threshold (XB) (step 7).

To monitor the concentration of detergent or other additives in the aqueous liquid in a tub, optical or electrochemical sensors are generally used, e.g. turbidity sensors, impedance sensors. It should be taken into account that detergents for forming a washing solution for cleaning laundry items contain in particular surfactants as surface-active substances, whereby these reduce the surface tension of the water in the aqueous solution formed (washing solution), since the surfactants prefer to be on the surface and thus on an interface adsorb. In particular, a surfactant concentration in an aqueous liquid in the tub must be monitored.

The signals from the sensors can be distorted and can only be evaluated poorly or not at all if the aqueous liquid to be measured is is not sufficiently calmed and/or there is too much foam in the aqueous liquid. This can lead to no evaluable results being obtained, particularly when using impedance sensors as electrochemical sensors.

The EP 0 383 218 B1 describes a method for controlling the rinsing of a program-controlled washing machine, which carries out several rinsing programs following a washing process, the electrical conductivity of the rinsing water being measured and the rinsing being ended when the difference between the measured conductance and a reference conductance falls below a predetermined level, whereby the conductivity measurement is carried out in a section of the drain line in which there is still liquid after the washing machine room has been emptied, and the conductance measurement is carried out after completion of a rinsing process on the rinsing water standing in the section, and depending on the result of the conductance measurement, a decision is made as to whether another Rinsing process is carried out. The conductivity measurement is preferably carried out in a calm pump sump.

The FR 2 455 648 A1 describes a method for monitoring and controlling a program, in particular the admission of water and/or the addition of cleaning agents or fabric softeners, into automatic washing machines or dishwashers. The machine is equipped with sensors that measure the surface tension and/or electrical conductivity of the washing liquid.

Against this background, the object of the present invention was to provide a method for operating a washing machine that is improved with regard to the measurement of electrochemical signals, in particular impedance signals from an impedance sensor. The method should preferably enable monitoring of a washing program to be as simple and/or accurate as possible. Another object of the invention was to provide a washing machine suitable for carrying out this method.

According to the invention, this object is achieved by a method and a washing machine according to the independent patent claims. Preferred embodiments of the Invention are listed in the respective dependent patent claims. Preferred embodiments of the method correspond to preferred embodiments of the washing machine, even if this is not specifically pointed out here.

1. (a) Bereitstellung im Behälter einer waschmittelhaltigen wässrigen Flüssigkeit;
2. (b) Drehung der Trommel nach einem vorbestimmten Bewegungsprogramm;
3. (c) Beenden einer Drehbewegung der Trommel und Ruhenlassen der waschmittelhaltigen wässrigen Flüssigkeit, bis ein vorgegebener beruhigter Zustand der waschmittelhaltigen wässrigen Flüssigkeit erreicht ist; und
4. (d) Messung der Konzentration c_ten eines Waschmittels in der im Schritt (a) bereitgestellten waschmittelhaltigen wässrigen Flüssigkeit durch Aufnahme und Auswertung von elektrochemischen Signalen des elektrochemischen Sensors unter Verwendung eines in der Steuereinrichtung hinterlegten Zusammenhangs zwischen elektrochemischen Signalen und Waschmittelkonzentrationen;

wobei als Maß für einen beruhigten Zustand im Schritt (c) mit dem elektrochemischen Sensor eine Stromspannungskurve aufgenommen wird und in Hinblick auf einen nicht durch Diffusion zum elektrochemischen Sensor bedingten Stromanteil ausgewertet wird, und wobei der nicht durch Diffusion zum elektrochemischen Sensor bedingte Stromanteil einen Beitrag von Konvektion umfasst.The invention therefore relates to a method for operating a washing machine with a container, a drum for holding items of laundry, a drive motor for the drum, an electrochemical sensor in the container for measuring an electrochemical signal depending on a composition of an aqueous liquid in the container, and a Control device, whereby the following steps are carried out:

1. (a) providing an aqueous liquid containing detergent in the container;
2. (b) rotating the drum according to a predetermined movement program;
3. (c) stopping rotation of the drum and allowing the detergent-containing aqueous liquid to rest until a predetermined calm state of the detergent-containing aqueous liquid is reached; and
4. (d) measuring the concentration c _th of a detergent in the detergent-containing aqueous liquid provided in step (a) by recording and evaluating electrochemical signals from the electrochemical sensor using a relationship between electrochemical signals and detergent concentrations stored in the control device;

wherein a current voltage curve is recorded with the electrochemical sensor as a measure of a calm state in step (c) and is evaluated with regard to a current component that is not caused by diffusion to the electrochemical sensor, and wherein the current component that is not caused by diffusion to the electrochemical sensor makes a contribution of Convection includes.

The term “aqueous liquid containing detergent” is to be interpreted broadly. Detergent here means a detergent as such, including its components surfactants, enzymes, bleach, etc., as well as fabric softener. In addition, the detergent-containing aqueous liquid can also be referred to as washing liquor, for example free liquor, or rinsing liquid, depending on a phase in a washing program in which it is produced.

Furthermore, for the purposes of the invention, a container is understood to mean a tub, a part of the container or a component in which the aqueous liquid provided during operation of the washing machine is located or flows past. The impedance sensor can thus be arranged in the tub of a washing machine as well as in a measuring container that is communicatively connected to the tub or in a liquid line through which the aqueous liquid flows during operation of the washing machine. The latter could be particularly advantageous if the washing machine has a pumping system that removes the aqueous liquid from a tub and feeds it back in during operation of the washing machine.

The contribution of convection to the transport processes in the aqueous liquid is used as a measure of a given calm state.

To determine a sufficiently calm state of the aqueous liquid, the invention takes into account the fact that many electrochemical measurement methods generate electrochemical signals in the resting state of the aqueous liquid, the Faraday component of which is determined by the diffusion of electroactive species present in the aqueous liquid. If the aqueous liquid is not at rest, the transport of electroactive species to the electrode is no longer only due to diffusion, but also influenced by convection. This generally leads to characteristic changes in the electrochemical signal, the changes being a measure of the contribution of convection. By evaluating the electrochemical signals, it is possible to conclude that there is a contribution from convection and thus that the aqueous liquid may not be sufficiently calmed down. Suitable electrochemical signals can be measured, for example, using voltammetric methods. Such electrochemical signals can be obtained, for example, by using cyclic voltammetry, chronoamperometry or double-pulse chronoamperometry, but also by impedance spectroscopy.

In cyclic voltammetry, starting from a starting voltage at a generally constant speed, the voltage at a working electrode of the electrochemical sensor up to a so-called reversal voltage U _λ , which is sufficient for an oxidation or reduction process, changed (so-called "hinsweep"). The direction of the voltage change is then reversed and the voltage is changed back to the starting voltage (“backsweep”). During the outward sweep, the resulting current generally increases to a peak value I _p and then drops to a value I _λ up to the reversal potential U _λ . The ratio I _p /I _λ is often a characteristic quantity I _p /I _λ ^theorize when controlling the diffusion of the electrode processes. If a solution to be examined voltammetrically is in motion, this means the presence of convection, which generally leads to a decrease in I _p /I _λ . As a result, a then measured value I _p /I _λ ^real or the difference ΔI = I _p /I _λ ^theor - I _p /I _λ ^real can be used as a measure of a contribution from convection and thus as a measure of a calm state of the aqueous liquid viewed and used.

In chronoamperometry, a voltage jump is generally made to a suitable voltage that is sufficient for an oxidation or reduction process and a current drop is then measured and evaluated as a function of time. A convective contribution generally leads to a weakening of the current drop. In double-pulse chronoamperometry, a jump is then made back to the starting voltage and a current drop is measured and evaluated at the starting voltage again as a function of time.

In the method according to the invention, a current voltage curve is therefore recorded in step (c) as a measure of a calm state and evaluated with regard to a current component that is not caused by diffusion to the electrochemical sensor.

For this purpose, a cyclic voltammogram is particularly advantageously recorded and the peak current I _p during the sweep to a reversal potential U _λ and the current I _λ at the reversal potential U _λ are evaluated with regard to the current component that is not caused by diffusion to the electrochemical sensor.

Alternatively or in addition to this, a potential jump can be carried out using the electrochemical sensor and a current-time curve obtained can be evaluated for a non-diffusion-related portion as a measure of a calmed state, ie a lack of calming, of the aqueous liquid. Included The potential jump occurs in particular to a potential at which a component in the aqueous liquid is reversibly or irreversibly oxidized or reduced.

When we talk about potential changes at the electrochemical sensor, what is meant in particular is a potential change at the working electrode of the electrochemical sensor forming the electrochemical sensor. Accordingly, diffusion and convection are meant with regard to the transport of substances to the working electrode.

In a particularly preferred embodiment of the method according to the invention, in step (c) the detergent-containing aqueous liquid is left to rest for a predetermined period of time Δt _set . To determine Δt _set , an amount of the aqueous liquid, a load amount of laundry items and/or the movement program carried out in step (b) are preferably taken into account, with a relationship stored in the control device between the period Δt _set , the amount of aqueous Liquid, the amount of laundry and / or the exercise program carried out in step (b) is used.

The amount of aqueous liquid can be determined, for example, by measuring an amount of water introduced into the container using a water meter, taking into account the proportion of the introduced water absorbed by the laundry items and the so-called free liquor can be determined if, for example, a hydrostatic pressure sensor is arranged in the container and is used to measure the hydrostatic pressure as a measure of the free fleet.

The load amount of laundry items can be set by a user or preferably determined automatically in the washing machine. The load quantity can be determined by measuring the increase in weight of the drum due to the loading of laundry items or by analyzing the suction behavior of water by analyzing the change in hydrostatic pressure while adding water to dry laundry items. For this purpose, a hydrostatic sensor is advantageously present in a washing machine according to the invention. A water quantity counter, ie a measuring device for determining the amount of water filled in or the amount of washing solution filled in, is then also particularly advantageous. For example, with the help of Hydrostatic pressure p measured by the hydrostatic sensor can be compared with the amount of water filled. The laundry items in the drum absorb water. The absorbed water cannot contribute to an increase in hydrostatic pressure. By comparing the measured hydrostatic pressure p and the amount of water added - the absolute values and their change over time - with corresponding values for the moisture penetration of laundry items stored in the control device of the washing machine, the load quantity of laundry items and, if applicable, their degree of moisture penetration (degree of wetting) can be determined. determine.

In a further preferred embodiment, the dependence of the electrochemical signals on an existing amount or concentration of foam is taken into account for the detergent-containing aqueous liquid to rest until a predetermined calm state of the detergent-containing aqueous liquid is reached, the number and duration of sudden current drops being the measure be taken into account for an existing foam. The presence and amount of foam can be determined in different ways.

For example, the detection of foam in a washing machine can be done via a conductance measurement with two electrodes in the lower area of a container. In addition, foam detection when spinning a drum is possible by evaluating the target/actual speed difference. This takes advantage of the fact that foam can brake a rotating drum, resulting in a difference between the target and actual speed. The association between a specific foam concentration and the target/actual speed difference is generally stored in the control device of the washing machine. The presence of foam (liquid-air mixture) is often detected by a build-up of pressure during washing or spinning or by a greatly slowed decrease in pressure when pumping out.

In general, to detect the formation of foam, the hydrostatic pressure in a container is measured using a sensor. A pressure sensor, in particular a hydrostatic pressure sensor, is usually used for this, which is also suitable for determining the water level in the container as described above. Due to the imbalance of the laundry and the remaining water present, this can happen During the spin cycle, measurement errors can occur due to the appearance of an apparent increase in pressure. The appearance of pressure peaks can indicate the presence of foam even when there is no foam. This is due to fluctuations in pressure measurement with a sensor, and the errors in signal acquisition, conversion or processing also depend on whether a digital or analogue controller is used. Since sometimes negative values are not detected by a sensor, it is not the true average value that would result if negative components were also detected, but rather an increased pressure of the oscillating amount of water. The signals measured by the pressure sensor also increase with the speed, so that the pressure threshold specified for foam detection is exceeded prematurely. Foam can therefore advantageously be detected in a washing machine by measuring a signal S _n from a sensor for determining a signal from a liquid in the container and possibly containing foam while the drum is rotating at a high speed U _n and with one of this speed U _n associated value W _n stored in the program control are compared, with value pairs U _n and W _n (n≥1) being stored in the control device for at least two speeds and when the value W _n is reached or exceeded, ie when the condition S is fulfilled _n ≥W _n , the presence of foam is registered. The sensor can be an optical measuring system, a conductometric measuring system or a capacitive measuring system. A hydrostatic pressure sensor is preferred, in which a hydrostatic pressure p and/or a negative time gradient of the hydrostatic pressure (dp/dt), preferably a hydrostatic pressure p, of a liquid-air mixture located in the container is measured as a signal. The signal S _n and the assigned value W _n are then in particular pressure values.

In a preferred embodiment of the method according to the invention, the presence of foam in the aqueous liquid is therefore determined using a hydrostatic pressure sensor and taken into account for determining the calm state of the aqueous liquid.

Furthermore, the presence of foam is also reflected in electrochemical signals. If there is foam in front of the electrode, a measured current normally drops. The number and duration of such sudden power drops can therefore be used as a measure of an existing one Foam can be taken into account, whereby the time period Δt for calming (also referred to as “reversing pause” or “drum standstill phase”) can then be extended appropriately until the foam concentration has reduced to an acceptable level.

The method used to detect foam will generally depend on which phase of a washing program, i.e. in particular whether in a wetting phase, washing phase, rinsing phase or fabric softening phase, sufficient calming of the aqueous solution is to be ensured so that meaningful electrochemical signals can be recorded .

If a pressure sensor, in particular a hydrostatic pressure sensor, is present in the washing machine used, a measured pressure increase during a calming phase, i.e. drum standstill phase, due to aqueous liquid dripping from the laundry items can also be used as a measure of a calming of the aqueous liquid. As time goes on, the amount of liquid dripping will decrease.

If a predetermined period of time Δt _set is specified, the invention provides that the electrochemical sensor is used to check whether the aqueous liquid has actually calmed down sufficiently. As mentioned above, this can be done by determining a convection-related portion of the mass transport to the working electrode. If this is not the case, the predetermined period Δt _set can be adjusted and in particular extended. It can advantageously be provided that a maximum period Δt _set ^max is not exceeded. When Δt _set ^max is reached or exceeded, the movement program of the drum is advantageously adjusted and in particular the input of mechanical energy is reduced. This ensures that the drum does not take too long to stop rotating.

The input of mechanical energy takes place via a suitable movement program for the drum. The movement program in step (b) of the method according to the invention includes in particular a switch-on time [in %], a duration of a reversing cycle [in sec] and a speed [rpm] of the drum. The switch-on time is the portion of time in a phase of a washing program during which the drum rotates. This switch-on time is, for example, preferably 60 to 70% in a first rinsing step. A reversing cycle is generally the period of time that results from the periods: rotating the drum in one direction, resting the drum, rotating the drum in the opposite direction, resting the drum.

The type of electrochemical measurement method used in step (d) is also advantageously used to determine sufficient calming and in particular the determination of a predetermined period of time Δt _set , since electrochemical measurement methods can require different measurement times and resting states of the aqueous liquid.

The recording of electrochemical signals is particularly accurate if there is comparatively little dirt and/or foam in the aqueous liquid to be examined. This is particularly the case in a wetting phase and in a rinsing phase. In a preferred embodiment of the method according to the invention, steps (c) and (d) are therefore carried out in a wetting phase and/or in a rinsing phase.

The wetting phase here is understood to be the phase in a washing program in which items of laundry to be cleaned and in particular items to be washed with detergent solution are wetted with a detergent solution to be used for this purpose, generally until the items of laundry are saturated with the detergent solution. The items of laundry are generally only moved slightly or not at all. Therefore, in a wetting phase, there is generally only a slight separation of dirt from the items of laundry to be washed. In particular, a laundry drum is preferably not rotated at a speed of more than 25 revolutions per minute in a wetting phase. Herein, “washing liquor” and “surfactant-containing aqueous liquid” generally have the same meaning. The term “surfactant” as used herein means a single surfactant as well as a mixture of different surfactants.

The extent to which an aqueous liquid is moved through an agitation program and therefore requires a subsequent drum standstill phase also depends on the presence and shape of laundry carriers in the drum.

If the shape of the laundry carriers is asymmetrical, their contribution to the movement of the aqueous liquid at a given rotational speed of the drum will depend on the direction of rotation. Therefore, in the case of an asymmetrical shape of the laundry carriers used in the drum, at least the direction of rotation of the drum is taken into account before a drum standstill phase.

According to the invention, step (c) and/or step (d) are preferably carried out taking into account the type and/or amount of soiling on the laundry items, with a connection in the control device between the electrochemical signals and the detergent concentrations for different types and/or amounts of soiling the laundry items are deposited.

For example, if there is contamination with oil, non-ionic surfactants in particular could dissolve to a greater or lesser extent in the oil and would no longer be recorded when measuring the detergent concentration. On the other hand, ionic surfactants can be intercepted to a certain extent by contamination containing ions, i.e. consumed, so that they are no longer detected when measuring electrochemical signals.

The type and/or amount of dirt can be set by a user of the washing machine or measured by suitable sensors. The electrochemical sensor provided according to the invention, e.g. impedance sensor, is particularly suitable for this purpose. However, other sensors such as a turbidity sensor can also be used.

The electrochemical sensor is generally an electrode system consisting of at least two electrodes. When using a three-electrode arrangement, consisting of a working electrode, a counter electrode and a reference electrode, the potential at the working electrode, which is responsible for recording the electrochemical signals, can be set particularly precisely.

In any case, according to the invention, a single electrode system can be used for recording different electrochemical signals, for example for cyclic voltammetry or impedance spectroscopy, in which the electrochemical sensor is also known as an impedance sensor. According to the invention, the electrochemical sensor in step (d) is preferably used as an impedance sensor. The impedance sensor records impedance signals as electrochemical signals.

In the method according to the invention, the recording and evaluation of the impedance signals is generally carried out by applying electrical alternating voltage with varying frequencies to the impedance sensor and evaluating the impedance signals with regard to the phase angle φ and the magnitude of the impedance. The phase angle ϕ and the magnitude of the impedance can then be evaluated with regard to the type, amount and concentration of detergents, in particular surfactants and also micelle concentrations.

For measurement, an impedance spectrum is generally recorded using a suitable electrode system as an impedance sensor. As a rule, the impedance of an electrochemical system is examined as a function of the frequency of an alternating voltage at the working electrode. Various representations are known to those skilled in the art for representation, such as the Nyquist representation, in which the real part or the imaginary part of the impedance are represented as a function of the applied alternating voltage frequency. In general, a few characteristic points are suitable for characterizing the impedance spectrum when examining wash liquors (cf. EP 2 767 825 A1 ), for example at the maximum of the imaginary part in a lower frequency range or at the minimum of the imaginary part in an upper frequency range. From the impedance and frequency values at the characteristic points, typical parameters for an aqueous liquid containing detergent can generally be derived. For example, the conductivity of the liquid can be determined from the real part of a point. By evaluating the impedance at this point and the frequency at another point, the capacity of the so-called conductivity measuring cell formed by the impedance sensor and the aqueous liquid containing detergent can generally be determined. Another measure that depends on the properties of the aqueous liquid containing detergent is the flattening of a semicircle in the Nyquist representation, which is determined by the ratio of height to width of the Semicircle can be determined. The evaluation is done using formulas known to those skilled in the art.

In a particularly preferred embodiment of the invention, the impedance signals are evaluated with regard to electrical conductivity as a measure of the water hardness of the aqueous liquid.

According to the invention, impedance signals are therefore preferably recorded with the impedance sensor, the recording and evaluation of the impedance signals being carried out by applying electrical alternating voltage with varying frequencies to the impedance sensor and evaluating the impedance signals with regard to the phase angle ϕ and the magnitude of the impedance. It is particularly preferred that the impedance signal is recorded at a predetermined frequency of the alternating voltage.

A washing phase generally follows a wetting phase. If a washing program is signaled that there is sufficient wetting of the laundry, for example by reaching a predetermined threshold value p ₁ for the hydrostatic pressure p and a predetermined threshold value (Δp / Δt) ₁ for the time gradient of the hydrostatic pressure p, it begins in Generally the washing phase. Monitoring a detergent concentration with an electrochemical sensor is particularly useful during a washing phase. This makes it possible to determine the consumption of detergent and thus any need for additional detergent dosage. In addition, a washing program can be optimally adjusted to a determined detergent concentration.

1. (a) Bereitstellung im Behälter einer waschmittelhaltigen wässrigen Flüssigkeit;
2. (b) Drehung der Trommel nach einem vorbestimmten Bewegungsprogramm;
3. (c) Beenden der Drehbewegung der Trommel und Ruhenlassen der waschmittelhaltigen wässrigen Flüssigkeit, bis ein vorgegebener beruhigter Zustand der waschmittelhaltigen wässrigen Flüssigkeit erreicht ist; und
4. (d) Messung der Konzentration c_ten eines Waschmittels in der im Schritt (a) bereitgestellten waschmittelhaltigen wässrigen Flüssigkeit durch Aufnahme und Auswertung von elektrochemischen Signalen des elektrochemischen Sensors unter Verwendung eines in der Steuereinrichtung hinterlegten Zusammenhangs zwischen elektrochemischen Signalen und Waschmittelkonzentrationen;

wobei als Maß für einen beruhigten Zustand im Schritt (c) mit dem elektrochemischen Sensor eine Stromspannungskurve aufgenommen wird und in Hinblick auf einen nicht durch Diffusion zum elektrochemischen Sensor bedingten Stromanteil ausgewertet wird, und wobei der nicht durch Diffusion zum elektrochemischen Sensor bedingte Stromanteil einen Beitrag von Konvektion umfasst.The invention also relates to a washing machine with a container, a drum for holding items of laundry, a drive motor for the drum, an electrochemical sensor in the container for measuring an electrochemical signal depending on a composition of an aqueous liquid in the container, and a control device, wherein the control device is set up to carry out a method which includes the following steps:

1. (a) providing an aqueous liquid containing detergent in the container;
2. (b) rotating the drum according to a predetermined movement program;
3. (c) stopping the rotation of the drum and allowing the detergent-containing aqueous liquid to rest until a predetermined calm state of the detergent-containing aqueous liquid is reached; and
4. (d) measuring the concentration c _th of a detergent in the detergent-containing aqueous liquid provided in step (a) by recording and evaluating electrochemical signals from the electrochemical sensor using a relationship between electrochemical signals and detergent concentrations stored in the control device;

wherein a current voltage curve is recorded with the electrochemical sensor as a measure of a calm state in step (c) and is evaluated with regard to a current component that is not caused by diffusion to the electrochemical sensor, and wherein the current component that is not caused by diffusion to the electrochemical sensor makes a contribution of Convection includes.

According to the invention, a washing machine is preferred in which a temperature sensor is arranged in the container and a relationship between electrochemical signals, for example impedance signals, and detergent concentrations is stored in the control device for various temperature values measured with the temperature sensor.

The washing machine according to the invention makes it possible to dispense with the turbidity sensor that is often present in a washing machine. However, in embodiments of the washing machine according to the invention, a turbidity sensor can also be present as a supplement.

A washing machine used here generally also has a heater and a drain system with a drain pump arranged at the bottom of a tub. In addition, a washing machine used herein generally also has laundry carriers and/or scoop devices.

Finally, the washing machine according to the invention can be a washing machine as such or a washer-dryer, i.e. a device that has the functions of a dryer and a washing machine.

The washing machine according to the invention preferably has an acoustic and/or optical display means for displaying one or more operating states.

An optical display means can be, for example, a liquid crystal display on which certain requests or instructions are indicated. Additionally or alternatively, light-emitting diodes can light up in one or more colors. For example, different colored displays can be used to show whether a washing phase is taking place at an optimal detergent concentration or not. It can also be indicated whether the measurements with the electrochemical sensor are carried out in a sufficiently calm aqueous liquid.

In the event of underdosing of detergent, a user of the washing machine can be given a message to add more detergent, whereby a quantity can also be specified. The dosage recommendation is displayed on the display as such or a display field thereof (herein referred to collectively as the “display display”).

The dosage recommendation can be shown on the display in the form of text and/or characters. A suitable text would be, for example, the direct request "Please dose "Green"", where "Green" is a reference to a dosing aid. Other colors can also be mentioned or other information can be given in text form. Alternatively or in addition to this, a color or a symbol could be displayed as a symbol, for example a circle, which can be filled to different extents to distinguish individual amounts of detergent.

In embodiments of the invention, knowledge of the amount of water or water lye flowing into the container is important. Preferably, a measuring device for determining the amount of water filled is therefore present in the washing machine according to the invention, for example a time measuring device for determining the opening period of an inlet valve for the water or a liquid quantity measuring device for measuring the amount of water filled.

The invention has numerous advantages. A method for operating a washing machine is provided, in which the monitoring of, for example, the detergent concentration in the wash liquor is carried out particularly precisely by means of an electrochemical sensor, in particular an impedance sensor. This is possible according to the invention by taking into account that an electrochemical Measurement and in particular the measurement of an impedance signal with an impedance sensor can be disturbed and the measured impedance signal can therefore be falsified if the solution has not calmed down sufficiently at the time of measurement. In particular, the invention makes it possible, by adjusting pauses when reversing the drum during wetting, washing and rinsing, to precisely determine the surfactant concentration and water hardness by means of an electrochemical sensor in a detergent-containing, in particular surfactant-containing, aqueous liquid, primarily through impedance spectroscopy and cyclic voltammetry To avoid incorrect measurements due to air bubbles, foam and currents trapped in the aqueous liquid.

By more precisely determining the actual detergent concentration in a washing program and taking appropriate measures, over- or under-dosing of detergent can be influenced in a timely manner. On the one hand, it can prevent the washing machine from foaming over, which can be associated with water damage in an apartment. On the other hand, excessive use of rinsing water, which would be necessary if excess detergent had to be removed from the laundry items, can be avoided. For example, a more precise determination of the concentration of ionic surfactants as well as a more precise setting and maintenance of a concentration range for ionic surfactants is also made possible.

The invention is illustrated below using a non-limiting embodiment of a washing machine according to the invention shown in the single figure. Shown is a schematic representation of the parts relevant to the invention of the first embodiment of a washing machine according to the invention, in which a method according to the invention can be carried out.

The washing machine 1 of the figure has a tub 2 in which a drum 3 is rotatably mounted and can be driven by the drive motor 5. For improved ergonomics, the axis of rotation 19 of the drum 3 is directed upwards from the horizontal by a small angle (eg 13°), so that the user of the washing machine 1 has easier access and insight into the interior of the drum 3. Through this arrangement, in cooperation with laundry carriers 14 and Scoop devices 17 for the detergent-containing aqueous liquid, for example washing liquor, 7 on the inner surface of the drum shell also intensify the flooding of the laundry items 4 with washing liquor 7. The laundry carriers 14 are asymmetrical in the embodiment shown here, so that the aqueous liquid 7 in the tub 2 is moved to different extents for the two possible directions of rotation of the drum 3 at the same rotational speed of the drum 3. This influence is taken into account in the control device 8, so that a method according to the invention can be carried out even more precisely.

An impedance sensor 10 is arranged as an electrochemical sensor in the induction bowl 12, which is generally an electrode system made up of several electrodes, for example two capacitor plates or a three-electrode arrangement. With the help of impedance sensor 10, a detergent present in the dispenser 12 or an aqueous liquid containing this detergent can be analyzed in order to obtain information about the detergent and thus about the design of a washing program.

The washing machine 1 also has a lye supply system, which includes a water connection fitting for the domestic water network 20, an electrically controllable valve 21 and a supply line 13 to the lye container 2, which can optionally also be guided via the detergent dispenser tray 12, from which the incoming water feeds detergent portions into the Can transport tub 2. There is also a heating device 16 in the tub 2 for heating water or washing suds 7. The valve 21 as well as the heating device 16 can be controlled by a control device 8 depending on a program flow chart that is linked to a time program and / or to the achievement of certain Measured values of parameters such as lye level, lye temperature, speed of the drum, etc. can be tied within the washing machine 1.

6 means a pressure sensor, ie a sensor for measuring the hydrostatic pressure, in the tub 2. The hydrostatic pressure p results from the fill level of the free liquor 7 forming in the tub 2. In addition, the washing machine 1 includes a measuring device 15 for determining the amount of water filled, e.g. a water meter or a flow meter. in case of a Using the flow meter, the amount of water flowing in is calculated in conjunction with a recorded filling time. The flow can also be determined by measuring the time until a predetermined level is reached, which corresponds to a certain fixed amount of water. 18 means a drain pump for pumping out the washing suds 7.

In the figure, 9 denotes an electrochemical sensor in the tub 2, with which various electrochemical measurements can be carried out, for example voltammetric measurements or impedance measurements. The electrochemical sensor is preferably used as an impedance sensor, although its structure consisting of electrodes and the implementation and evaluation of impedance signals measured with the impedance sensor are not shown in more detail here. To carry out a method according to the invention, the electrochemical signals from the electrochemical sensor 9 and possibly the impedance sensor 10 as well as the rotation speed of the drum 2, its loading with laundry items 4, the hydrostatic pressure, etc. and the measured values from the measuring device 15 are fed to the control device 8.

1. (a) Bereitstellung im Laugenbehälter 2 einer waschmittelhaltigen wässrigen Flüssigkeit 7;
2. (b) Drehung der Trommel 3 nach einem vorbestimmten Bewegungsprogramm, das in Abhängigkeit von einer Benetzungsphase, Waschphase oder Spülphase unterschiedliche Reversierschritte, Schleuderschritte usw. bei unterschiedlichen Rotationsgeschwindigkeiten der Trommel 3 umfassen kann;
3. (c) Beenden der Drehbewegung der Trommel 3 und Ruhenlassen der waschmittelhaltigen wässrigen Flüssigkeit 7, bis ein vorgegebener beruhigter Zustand der waschmittelhaltigen wässrigen Flüssigkeit 7 erreicht ist; und
4. (d) Messung der Konzentration c_ten eines Waschmittels in der im Schritt (a) bereitgestellten waschmittelhaltigen wässrigen Flüssigkeit 7 durch Aufnahme und Auswertung von elektrochemischen Signalen des elektrochemischen Sensors 9 unter Verwendung eines in der Steuereinrichtung 8 hinterlegten Zusammenhangs zwischen elektrochemischen Signalen und Waschmittelkonzentrationen.

Carrying out the method according to the invention includes the following steps:

1. (a) providing an aqueous liquid 7 containing detergent in the tub 2;
2. (b) rotation of the drum 3 according to a predetermined movement program, which may include different reversing steps, spinning steps, etc. at different rotation speeds of the drum 3 depending on a wetting phase, washing phase or rinsing phase;
3. (c) stopping the rotation of the drum 3 and allowing the detergent-containing aqueous liquid 7 to rest until a predetermined calm state of the detergent-containing aqueous liquid 7 is reached; and
4. (d) measuring the concentration c _th of a detergent in the detergent-containing aqueous liquid 7 provided in step (a) by recording and evaluating electrochemical signals from the electrochemical sensor 9 using a relationship between electrochemical signals and detergent concentrations stored in the control device 8.

In step (c), the resting of the detergent-containing liquid 7 is monitored with the electrochemical sensor 9, with a measurement using cyclic voltammetry, chronoamperometry or impedance spectroscopy preferably being carried out to determine a predetermined calm state of the detergent-containing liquid 7.

In step (d), in the embodiment shown here, the concentration c _th of a detergent in the detergent-containing aqueous liquid 7 is measured by recording and evaluating impedance signals from the electrochemical sensor 9 functioning as an impedance sensor 9, with a relationship between impedance signals stored in the control device 8 and detergent concentrations are used.

11 means a display device with which process parameters, in particular the running of a washing program with optimal use of detergent (e.g. represented by a green LED) or with non-optimal use of detergent (e.g. represented by a red LED) can be displayed. In particular, a dosage recommendation for a user of the washing machine can also be displayed.

Reference symbol list

1

washing machine

2

Lye container

3

drum

4

laundry items

5

drive motor

6

Pressure sensor

7

aqueous liquid, free liquor, wash liquor

8th

Control device

9

electrochemical sensor in the tub, e.g. impedance sensor; Electrode arrangement for measuring impedance

10

Impedance sensor in the dispenser bowl; Electrode arrangement for measuring impedance

11

Display device

12

(Detergent) dispenser bowl

13

Supply line to the tub

14

Laundry take-out

15

Measuring device for determining the amount of water filled

16

Heating device

17

scooping device

18

Pump, drain pump

19

Axis of rotation

20

Water supply, domestic water network, water supply

21

(electrically controllable) valve

22

Temperature sensor

Claims (14)

1. Method for operating a washing machine (1) having a tub (2), a drum (3) for receiving items of laundry (4), a drive motor (5) for the drum (3), an electrochemical sensor (9) in the tub (2) for measuring an electrochemical signal as a function of a composition of an aqueous liquid (7) in the tub (2), and a control facility (8), wherein the following steps are carried out:

   (a) providing an aqueous liquid (7) containing detergent in the tub (2);

   (b) rotating the drum (3) according to a predetermined movement program;

   (c) terminating a rotational movement of the drum (3) and allowing the aqueous liquid (7) containing detergent to rest until a predetermined calm state of the aqueous liquid (7) containing detergent is reached; and

   (d) measuring the concentration c_ten of a detergent in the aqueous liquid (7) containing detergent and provided in step (a) by recording and evaluating electrochemical signals of the electrochemical sensor (9) using an association between electrochemical signals and detergent concentrations stored in the control facility (8),

   wherein a current voltage curve is recorded with the electrochemical sensor (9) as a measure of a calm state in step (c) and is evaluated in respect of a proportion of electricity not conditioned by diffusion with respect to the electrochemical sensor (9),

   and wherein the proportion of electricity conditioned by diffusion with respect to the electrochemical sensor (9) comprises a contribution of convection.
2. Method according to claim 1, characterised in that a cyclic voltammogram is recorded and the peak current I_p is evaluated when sweeping towards a reverse potential U_λ and with a reverse potential Uλ in respect of the proportion of electricity not conditioned by diffusion with respect to the electrochemical sensor (9).
3. Method according to one of claims 1 to 2, characterised in that a potential jump is carried out by using the electrochemical sensor (9) and a current-time curve obtained in the process is evaluated for a non-diffusion-conditioned portion as a measure of a missing calming of the aqueous liquid.
4. Method according to one of claims 1 to 3, characterised in that in step (c), the aqueous liquid (7) containing detergent is allowed to rest for a predetermined period of time (Δt_set).
5. Method according to claim 4, characterised in that a quantity of aqueous liquid (7), a quantity of items of laundry (4) and/or the movement program carried out in step (b) is taken into account in order to determine Δt_set, wherein an association between the period of time Δt_set stored in the control facility (8), the quantity of aqueous liquid (7), the quantity of items of laundry (4) and/or the movement program carried out in step (b) is used.
6. Method according to one of claims 1 to 5, characterised in that in order to allow the aqueous liquid containing detergent to rest until a predetermined calm state of the aqueous liquid (7) containing detergent is reached, the dependency of the electrochemical signals on an existing quantity or concentration of foam is taken into account, wherein the number and duration of sudden power drops are taken into account as a measure of an existing foam.
7. Method according to claim 6, characterised in that the presence of foam in the aqueous liquid (7) is determined with a hydrostatic pressure sensor (6) and taken into account for determining the calm state of the aqueous liquid (7).
8. Method according to one of claims 1 to 7, characterised in that the steps (c) and (d) are carried out in a wetting phase and/or in a rinsing phase.
9. Method according to one of claims 1 to 8, that with a non-symmetrical form of laundry agitators (14) used in the drum (3), at least the direction of rotation of the drum (3) is taken into account before a drum standstill phase.
10. Method according to one of claims 1 to 9, characterised in that step (c) and/or step (d) are carried out by taking into account the type and/or quantity of dirt in the items of laundry (4), wherein an association between the electrochemical signals and the detergent concentrations for different types and/or quantities of dirt in the items of laundry (4) are stored in the control facility (8).
11. Method according to one of claims 1 to 10, characterised in that the electrochemical sensor (9) is used as an impedance sensor in step (d).
12. Method according to claim 11, characterised in that impedance signals have been recorded with the impedance sensor (9), wherein the recording and evaluation of the impedance signals is carried out by electrical alternating voltage with varying frequencies being applied to the impedance sensor (9) and the impedance signals being evaluated in respect of the phase angle φ and the sum of the impedance.
13. Method according to claim 12, characterised in that the impedance signal is recorded with a predetermined frequency of the alternating voltage.
14. Washing machine (1) with a tub (2), a drum (3) for receiving items of laundry (4), a drive motor (5) for the drum (3), an electrochemical sensor (6, 9) in the tub (2) for measuring an electrochemical signal as a function of a composition of an aqueous liquid (7) in the tub (2), and a control facility (8), characterised in that the control facility (8) is designed to carry out a method, which comprises the following steps:

    (a) providing an aqueous liquid (7) containing detergent in the tub (2);

    (b) rotating the drum (3) according to a predetermined movement program;

    (c) terminating the rotational movement of the drum (3) and allowing the aqueous liquid (7) containing detergent to rest until a predetermined calm state of the aqueous liquid (7) containing detergent is reached; and

    (d) measuring the concentration c_ten of a detergent in the aqueous liquid (7) containing detergent and provided in step (a) by recording and evaluating electrochemical signals of the electrochemical sensor (9) using an association between electrochemical signals and detergent concentrations stored in the control facility (8),

    wherein a current voltage curve is recorded as a measure of a calm state in step (c) with the electrochemical sensor (9) and is evaluated in respect of a proportion of electricity not conditioned by diffusion with respect to the electrochemical sensor (9),

    and wherein the proportion of electricity not conditioned by diffusion with respect to the electrochemical sensor (9) comprises a contribution of convection.

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