DE102017223002A1 - Household appliance for the care of laundry with measuring device for determining a load and method - Google Patents

Abstract

The invention relates to a domestic appliance (1) for the care of items of laundry (14), with a spring-suspended vibration system (8) for receiving the items of laundry (14) and with a measuring device (13) for determining a mass of the items of laundry (14) within the oscillation system (8), wherein the measuring device (13) comprises a sensor device (11) for determining a vibration of the vibration system (8) after loading the vibration system (8) with the laundry items (14) and a computing device (12) for determining the mass of the laundry items (14) based on the vibration, wherein the sensor device (11) is adapted to the vibration of the vibration system in a first direction (y) and at least in a direction different from the first direction (y), the second direction (x, z) determine and the computing device (12) is adapted to the mass of the laundry items (14) based on the vibration in the first direction (y) and in the at least one second Richtun g (x, z).

Description

The invention relates to a household appliance for the care of laundry, with a spring-mounted vibration system for receiving the laundry items and with a measuring device for determining a mass of the laundry items within the vibration system, wherein the measuring device with a sensor device for detecting a vibration of the vibration system after loading the vibration system the laundry items and a computing device for determining the mass of the laundry items based on the detected vibration. In addition, the present invention relates to a method for determining a mass of laundry items.

The interest is directed here to household appliances for the care of laundry, especially washing machines. Conventional washing machines have a spring system mounted in the housing vibration system, which serves to accommodate the laundry items. At the beginning of a washing program, which is carried out with the household appliance, the mass of the laundry items that are in the vibration system, or to determine the loading amount. For the measurement of the load in washing machines, one usually makes use of the static deflection of the vibration system due to the weight of the laundry. The deflection of the vibration system can be determined by means of a corresponding sensor device. This sensor device can have a one- or multi-dimensional position sensor with which the deflection of the vibration system can be determined. With a known design of the springs of the vibration system can then be closed to the mass of the laundry items.

Furthermore, measuring devices are known from the prior art, by means of which a vibration of the vibration system can be detected after loading and the mass of the laundry items can be estimated on the basis of the vibration with known properties of the springs. This describes the DE 10 2014 104 635 A1 a method for determining a type of textile of a washing load located in a treatment chamber, wherein the treatment chamber is defined by a rotatable drum of a laundry treatment device. It is provided that a first density of the wash load in a first wet state and a second density in a second wet state are determined. Based on the comparison of the first and the second density then the type of textile can be determined. In this case, the mass of the wash load can be determined by measuring the natural frequency of the drum and the wash load. To determine the natural frequency, the wash load can be excited with a pulse and the frequency response with a receiver, such as a microphone or an accelerometer, are monitored.

In addition, the describes DE 10 2011 084 267 A1 a laundry treatment device with a housing and with an oscillating suspended in the housing unit. In this case, it is provided that a monitoring device of the laundry treatment appliance has a vibration generator which is fixedly connected to the unit and a vibration receiver which is fixedly connected to the housing. With this monitoring device, the natural frequency of the unit can be determined. Thus, it is possible that the presence of a transport safety device is detected, since the natural frequency of the oscillating aggregate in a non-removed transport protection differs significantly from the natural frequency of the unit with removed transport protection.

It is an object of the present invention to provide a solution, as the mass of laundry within a household appliance can be determined in a simple manner reliable.

This object is achieved by a household appliance and by a method having the features according to the respective independent claims. Advantageous developments of the invention are specified in the dependent claims.

An inventive household appliance is used to care for items of laundry. The household appliance comprises a spring-suspended vibration system for receiving the laundry items. In addition, the household appliance comprises a measuring device for determining a mass of the laundry items within the vibration system, wherein the measuring device has a sensor device for detecting a vibration of the vibration system after loading the vibration system with the laundry items and a computing device for determining the mass of the laundry items based on the detected vibration. In this case, it is provided that the sensor device is designed to detect the oscillation of the oscillation system in a first direction and at least in a second direction different from the first direction. In addition, the computing device is designed to determine the mass of the laundry items based on the vibration in the first direction and in the at least one second direction.

The household appliance is used for the care of laundry items. The household appliance may be to act a washer-dryer. In particular, the household appliance is designed as a washing machine. The household appliance comprises a housing in which the vibration system is mounted swinging. In particular, the vibration system can be held by means of one or more springs in an interior of the housing. The vibration system serves to accommodate the items of laundry and may in particular comprise a washing drum into which the items of laundry can be introduced. This laundry drum can be rotated to maintain laundry by means of a motor. In addition, the vibration system may have a tub. Furthermore, the household appliance comprises the measuring device, by means of which the mass of the laundry items which are located within the vibration system or the laundry drum, can be determined. The measuring device in turn comprises the sensor device, by means of which the oscillation of the vibration system can be detected. The sensor device may particularly comprise a displacement sensor by means of which the deflection of the vibration system can be determined as a function of time. Furthermore, the measuring device comprises the computing device, which is connected to the sensor device for data transmission. By means of the computing device, the mass of the laundry items can be determined on the basis of the vibration detected by the sensor device. It is provided in particular that an oscillation frequency of the vibration system is determined after loading. Based on a known spring rate of the vibration system or the at least one spring of the vibration system, the mass of the vibration system including the laundry items can then be determined on the basis of known oscillation equations. Based on the known mass of the vibration system can then be deduced the mass of the laundry items. Using the vibration equations, the vibration system can be described together with the laundry as a spring-mass system or as a spring-mass-damper system.

According to an essential aspect of the present invention, it is provided that the sensor device can determine the oscillation both in a first direction and in at least a second direction. The computing device can then determine the mass of the items of laundry or the amount of loading on the basis of the oscillation in the first direction and on the basis of the oscillation in the at least one second direction. In this case, it is considered that the vibration system has different vibration characteristics in the first direction and in the second direction due to the design of the vibration system. These different vibration characteristics are characterized in particular by different natural frequencies or resonance frequencies of the vibration system in the first direction and in the second direction. For the oscillation in the first direction, the mass of the laundry items can be determined, for example, based on the frequency or natural frequency of the oscillation. Likewise, the mass may be determined based on the vibration in the second direction. Thus, for example, a value for the mass of the laundry items, which was determined based on the oscillation in the first direction, can then be compared with a value for the mass of the laundry items which was determined on the basis of the second oscillation. In this way, a plausibility check can be carried out. Overall, therefore, the mass of the laundry items or the load can be determined reliably more easily.

The sensor device is preferably designed to determine a first frequency of the oscillation in the first direction and a second frequency of the oscillation in the at least one second direction, and the arithmetic device is designed to measure the mass of the laundry items on the basis of the first frequency and a predetermined first spring rate for the oscillation in the first direction and based on the second frequency and a predetermined second spring rate for the oscillation in the at least one second direction to determine. In this case, the first frequency particularly describes the natural frequency of the vibration system vibrating in the first direction, in which the laundry items are arranged. The second frequency preferably describes the natural frequency of the oscillating vibration system in the second direction, in which the laundry items are arranged. Due to the mass of the laundry items, the first frequency is influenced compared to the vibration system in which there are no laundry items. On the basis of the determined first frequency and the known first spring rate, the mass of the vibration system including the laundry items can then be determined. The spring rate, which may also be referred to as the spring constant, indicates the ratio of the force acting on a spring to the deflection of the spring caused thereby. It can be assumed that the first frequency corresponds to the root of the quotient of the first spring rate and the mass of the vibration system including the laundry. Based on the known mass of the vibration system without laundry then the mass of the laundry items can be determined. When determining the mass of the laundry items, a known or predetermined damping constant for the oscillation in the first direction can additionally be taken into account. Likewise, the mass may be based on the second frequency and the second spring rate can be determined. This allows the determination of the mass with a low computational cost.

In one embodiment, the sensor device is configured to determine a first sensor signal, which describes the oscillation in the first direction, and at least one second sensor signal, which describes the oscillation in the at least one second direction, and the arithmetic device is designed to be the first Determine frequency based on the first sensor signal and the second frequency based on the second sensor signal. By means of the sensor device, the first sensor signal can be provided, which describes the vibration of the loaded vibration system in the first direction. The first sensor signal can be output by means of the sensor device, for example in the form of a time-varying electrical voltage. This first sensor signal can then be transmitted to the computing device. The computing device can have, for example, an analog-to-digital converter, by means of which the first sensor signal can be sampled or digitized. By means of the computing device, which may also have a microcontroller, a processor or the like, then the first sensor signal or the sampled first sensor signal can be processed. The first frequency can be determined. In the same way, the second sensor signal can be provided and processed. Thus, the first and second frequencies can be reliably determined. In a further embodiment, a first computing device can digitize the sensor signals and transmit them via a digital interface to a second computing device. The second computing device can take over the determination of the frequencies and the calculation of the mass.

Furthermore, it is advantageous if the computing device is designed to determine a first frequency spectrum of the first sensor signal and to determine the first frequency based on the first frequency spectrum and to determine a second frequency spectrum of the second sensor signal and to determine the second frequency based on the second frequency spectrum. The first sensor signal describes the vibration of the vibration system including the laundry in the first direction as a function of time. In particular, the computing device is designed to determine a frequency spectrum of the first sensor signal and to derive therefrom the first frequency or the natural frequency. To determine the first frequency based on the first sensor signal, for example, an FFT (fast Fourier transform) or the like can be used. This also applies to the determination of the second frequency.

Preferably, the computing device is configured to determine a first period of the oscillation in the first direction and to determine the first frequency based on the first period and at least determine a second period of the oscillation in the at least one second direction and the second frequency based on the second Period to determine. In particular, the first sensor signal describes the time profile of the oscillation of the oscillation system in the first direction. By means of the computing device, for example, the maxima of this time profile of the oscillation can be determined. Thereafter, the time duration between the oscillation maxima can be determined and from this the period duration can be derived. On the basis of the period then the first frequency of the oscillation or the natural frequency can be determined. In the same way, the second frequency of the oscillation in the second direction can be determined.

In a further refinement, the computing device is designed to determine in the first sensor signal a section which describes a free damped oscillation of the oscillation system in the first direction, and to determine the first frequency in the section and to determine a section in the second sensor signal , which describes a free damped vibration of the vibration system in the second direction, and to determine the second frequency in the section. By means of the computing device, the temporal portion of the first sensor signal can be determined, which describes the free vibration of the vibration system in which the laundry items are located. At the beginning of the washing process, for example, the shop opening or the window is opened by the user. Subsequently, the laundry items are inserted into the vibration system or the laundry drum. The free damped vibration is created by the loading process, in which the user of the household appliance (unintentionally) abuts the vibration system and then let oscillate freely for a moment. The proportion of the first sensor signal, which describes this free damped oscillation, can be detected by means of the computing device. For this purpose, the computing device can compare the first sensor signal with predetermined reference signals, which describe a free damped oscillation. Alternatively or additionally, this portion of the first sensor signal can be detected on the basis of the amplitude of the first sensor signal, a time profile of the first sensor signal or the like. If only the portion of the first sensor signal, including the free damped oscillation of the vibration system describes the laundry, is used to determine the first frequency, the mass of the laundry items can be reliably determined. The same applies to the corresponding proportion in the second sensor signal.

Furthermore, it is preferably provided that the sensor device is designed to determine the vibration of the vibration system in three mutually perpendicular directions. It is preferably provided that the sensor device can determine the vibration of the vibration system including the laundry items in three different spatial directions. This means that a first sensor signal, a second sensor signal and a third sensor signal are provided with the sensor device. By means of the computing device, in addition to the first frequency and the second frequency, it is also possible to determine the third frequency, which describes the oscillation in the third direction. On the basis of the first frequency, the second frequency and the third frequency, a value for the mass of the laundry items can then be determined in each case and the mass of the laundry items can be reliably estimated from the respectively determined values.

In particular, the sensor device is designed to determine the vibration of the vibration system in a height direction, a length direction and a width direction of the household appliance. It may also be provided that the first direction corresponds to the height direction of the household appliance, the second direction corresponds to the length direction of the household appliance and the third direction corresponds to the width direction of the household appliance. It can also be provided that the first direction runs in the axial direction of the laundry drum, the second direction runs radially to the laundry drum along the height direction of the household appliance and the third direction runs radially to the laundry drum along the width direction of the household appliance. The statements "depth direction", "width direction", "height direction", etc., indicate the positions and orientations given during intended use and proper positioning of the household appliance and in the case of an observer standing in front of the household appliance and looking in the direction of the household appliance.

According to a further embodiment, the sensor direction has a displacement sensor for determining a deflection of the vibration system in the first direction and in the at least one second direction. Preferably, the displacement sensor is designed as a magnetic displacement sensor. For example, the sensor device may comprise at least one magnetic sensor, in particular a Hall sensor, and a magnet, in particular a permanent magnet. For example, the magnetic sensor may be stationarily arranged on the vibration system and the magnet may be fixedly arranged on the housing of the household appliance or vice versa. By means of the magnetic sensor, the magnetic flux density and / or the field direction of the magnetic field of the magnet can be detected. From this, the relative position of the magnetic sensor to the magnet can then be determined. The sensor device may also have another displacement sensor, position sensor and / or acceleration sensor.

Furthermore, it is advantageous if the household appliance has at least one free-lift damper for damping the vibration of the vibration system. Such a free lift damper is characterized in particular by the fact that it has a low damping in the region of a rest position of the vibration system. As a result, the damping of the vibration system can be neglected and a simplified oscillation equation can be used to determine the mass of the laundry items. For example, the vibration system can be described as a spring-mass system. Thus, the mass of the laundry items can be determined with a low computational cost.

An inventive method is used to determine a mass of laundry items in a household appliance for the care of laundry. In this case, the mass of the laundry items within a vibration system for receiving the laundry items is determined by means of a measuring device, wherein a vibration of the vibration system is detected after loading the vibration system with the laundry items by means of a sensor device and determined by means of a computing device, the mass of the laundry items on the basis of the detected vibration becomes. In addition, it is provided that by means of the sensor device, the oscillation of the oscillation system in a first spatial direction and in at least one to the first direction different second direction is determined and by means of the computing device, the mass of the laundry items on the basis of the vibration in the first direction and in the at least a second direction is determined.

The preferred embodiments presented with reference to the household appliance according to the invention and their advantages apply correspondingly to the method according to the invention.

Further features of the invention will become apparent from the claims, the figures and the description of the figures. The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of the figures and / or shown alone in the figures are not only in the combination given, but also in other combinations usable, without departing from the scope of the invention. Thus, embodiments of the invention are to be regarded as encompassed and disclosed, which are not explicitly shown and explained in the figures, however, emerge and can be produced by separated combinations of features from the embodiments explained. Embodiments and combinations of features are also to be regarded as disclosed, which thus do not have all the features of an originally formulated independent claim. Moreover, embodiments and combinations of features, in particular by the embodiments set out above, are to be regarded as disclosed which go beyond the feature combinations set out in the back references of the claims or deviate therefrom.

• 1 eine schematische Frontansicht eines Ausführungsbeispiels eines erfindungsgemäßen Haushaltsgeräts zur Pflege von Wäschestücken;
• 2 einen zeitlichen Verlauf einer Schwingung eines Schwingungssystems des Haushaltsgeräts während und nach dem Beladen des Haushaltsgeräts mit Wäschestücken; und
• 3 einen zeitlichen Verlauf der freien gedämpften Schwingung des Schwingungssystems nach dem Beladen des Haushaltsgeräts mit Wäschestücken.

The invention will now be described with reference to preferred embodiments and with reference to the accompanying drawings. Showing:

• 1 a schematic front view of an embodiment of a household appliance according to the invention for the care of laundry items;
• 2 a time course of a vibration of a vibration system of the household appliance during and after the loading of the household appliance with laundry; and
• 3 a time course of the free damped oscillation of the vibration system after loading the household appliance with laundry.

In the figures, identical or functionally identical elements are provided with the same reference numerals.

In 1 is a simplified front view of a household appliance 1 for the care of laundry items, which may be for example a washing machine or a washer-dryer, shown. The household appliance 1 has a width direction x , a depth direction y and a height direction z on. The household appliance 1 includes a housing 2 in which a laundry drum 3 is rotatably mounted. A longitudinal axis or axis of rotation of the laundry drum 3 is in this embodiment in the illustration in 1 oriented perpendicular to the plane of the figure. The household appliance 1 also includes a tub 4 also in the case 2 is arranged and the laundry drum 3 surrounds. The laundry drum 3 includes a hollow cylindrical shell and a rear end wall and is also front open, so that here a feed opening is provided, which laundry items 14 in an interior 5 the laundry drum 3 can be introduced. The loading opening is through a door 6 lockable, which is movable on the housing 2 is arranged. The laundry drum 3 can by means of a drive motor 7 , which in the present case is indicated only schematically, are driven or rotated.

The laundry drum 3 and the tub 4 together form a vibration system 8th , which swinging on the housing 2 or in an interior of the housing 2 is stored. The vibration system 8th is with at least one spring 9 on the housing 2 held. In the present case is a spring 9 exemplified. There is also a damper 10 provided with which the vibration of the vibration system 8th can be dampened. In addition, the household appliance includes 1 a sensor device 11 , by means of which the vibration of the vibration system 8th relative to the housing 2 can be detected. It is envisaged that by means of the sensor device 11 the vibration of the vibration system 8th can be determined in different directions. In the present case, by means of the sensor device 11 the vibration of the vibration system 8th in the width direction x , the height direction y and the depth direction z be determined. The sensor device 11 can be designed in particular as a three-dimensional magnetic displacement sensor. In addition, the household appliance includes 1 a computing device 12 , which for data transmission with the transmitting device 11 connected is. The sensor device 11 and the computing device 12 Together they form a measuring device 13 , by means of which a mass of the laundry items 14 which are inside the laundry drum 3 can be determined.

2 shows a time course of a first sensor signal 15 , In the graph, the time is on the abscissa t and on the ordinate the way s of the first sensor signal 15 applied. This first sensor signal 15 is with the sensor device 11 output and describes the time course of the vibration of the vibration system 8th in a first direction, in the present case the height direction y of the household appliance 1 , This describes a first time t1 a beginning of the loading process. From the moment t1 the user starts the laundry 14 into the vibration system 8th or the laundry drum 3 contribute. The loading process lasts until a second time t2 on. During the loading process are significant fluctuations with relatively high paths s in the first sensor signal 15 to recognize. After the second time t2 or after the loading process leads the vibration system 8th a free damped vibration through. This free damped vibration is a section 16 of the first sensor signal 15 assigned.

wobei s(t) den gemessenen Schwingungsweg s in Abhängigkeit von der Zeit beschreibt. m ist die Masse des Schwingungssystems 8 inklusive der Wäschestücke 14, k ist die Dämpfungskonstante und D ist die Federrate. Die Dämpfungskonstante k und die Fehlerrate D für die Schwingung des Schwingungssystems 8 in der ersten Richtung beziehungsweise der Höhenrichtung y sind bekannt. Mit einer vereinfachten Form der Schwingungsgleichung reduziert sich der Aufwand der Messung auf die Bestimmung einer Periodendauer oder einer Frequenz der Schwingung des Schwingungssystems 8. Dabei ist es insbesondere vorgesehen, dass der Dämpfer 10 als sogenannter Freihubdämpfer mit einer extrem geringen Dämpfung in der Nähe der Ruhelage des Schwingungssystems 8 verwendet wird. Bei diesem Typ von Dämpfer 10 ist die vereinfachte Form der Schwingungsgleichung anwendbar. Eine erste Frequenz ω, welche die Schwingung in der ersten Richtung beschreibt, kann nach folgender Formel bestimmt werden: $$\mathrm{\omega =}{\left(\text{D/m}\right)}^{1\text{/}2}\text{.}$$

3 shows a time course of such a free damped oscillation of the vibration system 8th according to a further embodiment. Here describes the first sensor signal 15 a typical time course of a free damped oscillation. To describe this free damped vibration of the vibration system 8th a spring-mass damper system can be adopted. For this purpose, the following known oscillation equation can be used: $${\text{m * d}}^2\text{s}\left(\text{t}\right){\text{/ <figure-callout id="2" label="dt" filenames="DE102017223002A1\_0003.png" state="{{state}}">dt</figure-callout>}}^2+\text{k * ds}\left(\text{t}\right)\text{/ dt}+\text{D * s}\left(\text{t}\right).$$

where s (t) is the measured vibration path s depending on the time describes. m is the mass of the vibration system 8th including the laundry items 14 . k is the damping constant and D is the spring rate. The damping constant k and the error rate D for the vibration of the vibration system 8th in the first direction or the height direction y are known. With a simplified form of the oscillation equation, the expenditure of the measurement is reduced to the determination of a period duration or a frequency of the oscillation of the oscillation system 8th , It is particularly provided that the damper 10 as a so-called free-lift damper with an extremely low damping near the rest position of the vibration system 8th is used. In this type of damper 10 the simplified form of the oscillation equation is applicable. A first frequency ω , which describes the oscillation in the first direction, can be determined according to the following formula: $$\mathrm{\omega \; =}{\left(\text{Dm}\right)}^{1\text{/}2}\text{,}$$

The first frequency ω can by means of the computing device 12 based on the section 16 of the first sensor signal 15 be determined. For this purpose, by means of the computing device 12 for example, the frequency spectrum of the sensor signal 15 be determined. Alternatively or additionally, maxima M the sensor signal 15 be determined and from this the period tp be derived. Based on the first frequency ω and the known error rate D then can the mass m of the vibration system 8th including the laundry items 14 be determined. Based on the known mass of the vibration system can from this the mass of the laundry items 14 be derived.

It is envisaged that by means of the sensor device 11 for at least one further direction, a sensor signal is determined and from this the mass of the laundry items 14 is derived. For example, a sensor signal for the vibration of the vibration system 8th in the width direction x and / or in the depth direction z of the household appliance. The vibration system 8th points in the respective directions x . y . z a different vibration behavior, which is in the respective frequency ω or natural frequency reflects. Based on the respective frequency ω can then give values for the mass of the laundry items 14 be determined and compared with each other. Thus, the determination of the mass of the laundry items 14 be made plausible.

The evaluation of the frequency ω places much lower demands on the accuracy of the measuring device 13 compared to known systems, with which a lowering distance is evaluated. The disturbing influences from the damping system is reduced, in particular the sudden change of the damping force during loading (so-called slipping) has no influence on the sensor signal 15 , In this way, a cost reduction can be achieved because no special damper, such as spring piston damper, are required. The accuracy in the determination of the sensor signal 15 or the measured values improves in addition. This is due to the fact that the measured value is no longer dependent on the momentary rest position of the vibration system 8th dependent, which can be dispensed with a taring of the system.

LIST OF REFERENCE NUMBERS

1

household appliance

2

casing

3

washing drum

4

tub

5

inner space

6

door

7

drive motor

8th

vibration system

9

feather

10

damper

11

sensor device

12

computing device

13

measuring device

14

laundry

15

sensor signal

16

section

M

maximum

s

path

t

Time

t1

time

t2

time

tp

period

x

width direction

y

height direction

z

length direction

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102014104635 A1 [0003]
• DE 102011084267 A1 [0004]

Claims (12)

Household appliance (1) for the care of items of laundry (14), comprising a spring-loaded oscillation system (8) for receiving the items of laundry (14) and a measuring device (13) for determining a mass of the items of laundry (14) within the oscillation system (8), wherein the measuring device (13) based on a sensor device (11) for determining a vibration of the vibration system (8) after loading the vibration system (8) with the laundry items (14) and a computing device (12) for determining the mass of the laundry items (14) vibration, characterized in that the sensor device (11) is adapted to determine the vibration of the vibration system in a first direction (y) and at least in a second direction (x, z) different from the first direction (y) and the computing device (12) is adapted to measure the mass of the laundry items (14) on the basis of the oscillation in the first direction (y) and in the at least one second direction ( x, z). Household appliance (1) after Claim 1 , characterized in that the sensor device (11) is designed to determine a first frequency of the oscillation in the first direction (y) and a second frequency of the oscillation in the at least one second direction (x, z) and the computation device (12 ) is adapted to the mass of the laundry items (14) based on the first frequency (ω) and a predetermined first spring rate for the oscillation in the first direction (y) and based on the second frequency and a predetermined second spring rate for the vibration in the at least to determine a second direction (x, z). Household appliance (1) after Claim 2 , characterized in that the sensor device (11) is adapted to a first sensor signal (15) which describes the oscillation in the first direction (y), and at least one second sensor signal, which the oscillation in the at least one second direction (x , z), and the computing device is adapted to determine the first frequency based on the first sensor signal (15) and the second frequency based on the second sensor signal. Household appliance (1) after Claim 3 , characterized in that the computing device (12) is adapted to determine a first frequency spectrum of the first sensor signal (15) and to determine the first frequency based on the first frequency spectrum and to determine a second frequency spectrum of the second sensor signal and the second frequency on the basis of second frequency spectrum to determine. Household appliance (1) after Claim 3 , characterized in that the computing device (12) is adapted to determine a first period (tp) of the oscillation in the first direction (y) and to determine the first frequency based on the first period (tp) and at least one second period of the Determine oscillation in the at least one second direction (x, z) and to determine the second frequency based on the second period duration. Household appliance (1) according to one of Claims 3 to 5 characterized in that the computing means (12) is adapted to determine in the first sensor signal (15) a portion (16) which describes a free damped vibration of the vibration system (8) in the first direction (y) and determine first frequency on the basis of the section (16) and to determine in the second sensor signal a section which describes a free damped oscillation of the oscillation system (8) in the at least one second direction (x, z), and the second frequency based on the section to determine. Domestic appliance (1) according to one of the preceding claims, characterized in that the sensor device (11) is adapted to determine the oscillation of the oscillation system (8) in three mutually perpendicular directions (x, y, z). Domestic appliance (1) according to one of the preceding claims, characterized in that the sensor device (11) is adapted to the vibration of the vibration system (8) in a height direction (y), a length direction (x) and a depth direction (z) of the household appliance (1) to determine. Domestic appliance (1) according to one of the preceding claims, characterized in that the sensor direction (11) has a displacement sensor for determining a deflection of the vibration system in the first direction (y) and in the at least one second direction (x, z). Household appliance (1) after Claim 9 , characterized in that the displacement sensor is designed as a magnetic displacement sensor. Domestic appliance (1) according to one of the preceding claims, characterized in that the household appliance (1) has at least one damper (10) for damping the vibration of the vibration system (8), wherein the damper (10) is designed as a free-lift damper. Method for determining a mass of items of laundry (14) in a domestic appliance (1) for Care of items of laundry (14), wherein by means of a measuring device (13) the mass of the laundry items (14) within a vibration system (8) for receiving the laundry items (14) is determined, wherein a vibration of the vibration system (8) after loading of the Vibration system (8) with the laundry items (14) by means of a sensor device (11) is detected and by means of a computing device (12) the mass of the laundry items (14) is determined based on the detected vibration, characterized in that by means of the sensor device (11) Oscillation of the oscillation system (8) in a first direction (y) and in at least one second direction (x, z) different from the first direction (y), and by means of the computation device (12) the mass of the items of laundry (14) is determined on the basis of the oscillation in the first direction (y) and in the at least one second direction (x, z).

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