Abstract:
A washing machine is constructed with a special control unit and a conductance sensor in a washing liquid container for detecting a water level including whether there the water is above or below a given water level, and the presence of foam during a washing cycle. The control unit controls the operation of a pump, as well as the addition of fresh water, for eliminating excessive foam in the washing liquid container and in the drum. It is also possible to stop the pump from discharging this disturbing foam.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based on German Application No. 102006060256.0 filed on Dec. 14, 2006, of which the contents are hereby incorporated by reference. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to a method for controlling the operation of a washing machine, where a conductance sensor is placed in a washing liquid or powder container of the washing machine. 
       BACKGROUND OF THE INVENTION 
       [0003]    For controlling the operation of a washing machine it is for example known from US 2006/0191496 A1 or EP 633 342 A1 to place a conductance sensor in the interior thereof, for example in the lower area of the washing liquid container. The measured values of the conductance sensor are determined and evaluated by the washing machine control unit. However the possibilities for further processing or using these measured values as described therein are limited. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    Embodiments of the invention are described hereinafter relative to the attached diagrammatic drawings, wherein: 
           [0005]      FIG. 1  illustrates a diagrammatic inner view of one embodiment of an inventive washing machine; and 
           [0006]      FIGS. 2 to 4  illustrate different graphs for representing relationships between surfactant concentration, surface tension and conductance. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0007]    A problem addressed by the invention is to provide an aforementioned method with which the functionality of a washing process or operating process for the washing machine or the evaluation of an aforementioned conductance sensor can be improved. 
         [0008]    One embodiment is a method having the features of claims  1 ,  3 ,  5 ,  6 ,  9  or  12 . Advantageous and preferred embodiments of the invention form the subject matter of the further claims and are explained in greater detail hereinafter. It is in particular also possible to combine several of the aspects according to the invention. By express reference the wording of the claims is made into part of the content of the description. 
         [0009]    In a first basic embodiment of the invention, the conductance sensor detects the water level and, if said water level has dropped below the placing of the conductance sensor, an emptying of the washing liquid container is stopped, i.e., in particular, a pumping out with a pump is stopped. This makes it possible to prevent an idle running of the pump when the washing liquid container has been completely pumped empty, which on the one hand avoids unnecessary power consumption and on the other hand, in those phases where the drum does not rotate, prevents unpleasant, audible noises. 
         [0010]    Particularly if an aforementioned pump is provided for emptying the washing liquid container, it is advantageous for the switching off of the pump to take place with a few seconds delay after the water level has dropped below the conductance sensor. Such a delay can in particular be matched to the fact that with a normal pumping capacity the water level is admittedly lowered somewhat further below the conductance sensor, but an idle running of the pump or an intake of air at the same is avoided. This ensures that the pump is operated close to an optimum range, i.e., for emptying of the washing liquid container or a lowering of the water level to just above the pump. However, this is not essential, because the pump can also be switched off if the water level is below it. What is important is to establish where the water level is relative to the pump in order to avoid any noise. 
         [0011]    According to another basic embodiment of the invention, the conductance sensor is constructed to detect whether it is surrounded by foam during the washing process. This can not only be detected by the conductance sensor, but also in cooperation with the washing machine control unit or conductance sensor control unit. Fresh water is added as a countermeasure for the reduction or elimination of foam. Thus, the foam or liquid is at least diluted and as far as possible the foam removed. A detection of the foam on the conductance sensor is consequently possible with a high reliability level within the scope of the invention. Particularly in the case of capacitive conductance sensors, measured values for said foam state at the conductance sensor are between those for air and those for the case where said sensor is surrounded by water. 
         [0012]    It is advantageously also possible as a countermeasure when foam is present, to add fresh water in such a quantity or for so long as to ensure that during the washing process or during the drum rotation, the conductance sensor is essentially or particularly advantageously constantly surrounded by water. This avoids the negative effects of excessive foam during washing. 
         [0013]    According to another basic embodiment of the invention by means of the conductance sensor, it is possible to detect the surface tension of the washing liquid in the drum or in the liquid by determining the ionic concentration in the washing liquid. On the basis of this, it is possible to determine whether a specific surface tension is exceeded and a rinsing of the washing or laundry can be ended. In this way, it is possible to establish whether the detergent has been adequately rinsed out of the laundry. Thus, for example, as a function of the detected ionic concentration, the length or number of rinsing processes can be adapted accordingly. This is, in particular, continued until the ionic concentration or surface tension has exceeded a given, predetermined value and consequently the laundry is considered as being adequately rinsed. 
         [0014]    According to another basic embodiment of the invention, it is possible during the spin drying process, particularly with the pump constantly running, to increase the spin drying speed only until the conductance sensor is largely uninterruptedly or even constantly surrounded by water. This means that initially slow spin drying speeds are used, because then with the laundry still very wet, sufficient water is ejected from the said laundry, so that the water level is above the conductance sensor. Since as a rule the pumping capacity is limited or the pump always runs at its maximum capacity, it serves little purpose to spin dry the laundry even faster and eject even more water if this cannot be conveyed away in good time and sufficiently rapidly by the pump. Moreover, the laundry in the drum is constantly rotated through the water at the bottom of the washing liquid container and becomes wet again, which is to be avoided. 
         [0015]    It is advantageously additionally possible to only increase the spin drying speed when the conductance sensor after a long period of time, particularly a few minutes during which it was constantly or essentially surrounded by water, is no longer or is no longer essentially surrounded by said water. This means that then the pump can keep up with the water being removed from the laundry and can remove it and, as a result, the laundry can be spin dried with ever greater intensity and speed. With particular preference the spin drying speed can be slowly increased until the conductance sensor is again essentially or constantly surrounded by water. This can be repeated several times and the spin drying speed can be ever further increased. Due to this slow rise in the spin drying speed, an unnecessarily early or rapid spinning of the drum with the associated power consumption and bearing wear can be avoided. 
         [0016]    Advantageously by means of the conductance sensor and its measured values, a control of the pump operation is possible. It is possible on reaching a maximum spin drying speed to switch off said pump again if the conductance sensor is no longer or essentially no longer surrounded by water. It is advantageously only switched on again when the conductance sensor is constantly or essentially surrounded by water. Thus, it is possible to ensure that the pump is not continuously running at a maximum spin drying speed. Admittedly, the above-described idle running of the pump with an intake of air is not critical with respect to the noise burden during spin drying, especially at high speeds, because it is much less noisy than the spin drying operation. However, an unnecessary power consumption and wear to the pump can be reduced. 
         [0017]    It is particularly advantageously possible between a state change at the conductance sensor, i.e., a state when it is essentially surrounded by water and a state when it is essentially exposed and a switching on and off of the pump, to wait for a time interval of a few seconds, as described hereinbefore. This time interval can for example be in the range 5 to 30 seconds, particularly 10 to 20 seconds. As described hereinbefore, this brief time interval can also be provided to ensure that when the pump continues to run, further water is pumped out until just prior to pump idling. When the pump is stationary and the water rises there is a wait until the water level is just above the conductance sensor, but has not yet reached the laundry again. This reduces the pump operating frequency. 
         [0018]    According to another basic development of the invention, as stated hereinbefore, it is possible to determine on the conductance sensor whether it is surrounded by water, foam or air. Thus, during a spin drying process, the drum speed can be reduced if foam is detected at the conductance sensor. The reduction of the drum speed is a countermeasure for reducing foam formation, because the foam is then impacted less or no longer by the drum passing through it. A speed reduction can for example be 10 to 30%. In particular, the speed can be reduced slowly or in stages until the conductance sensor is no longer surrounded by foam. In certain circumstances it is even possible to completely stop the drum if the conductance sensor is still surrounded by foam. It is particularly advantageously possible, after stopping the drum, to wait for a few minutes, for example up to 5 minutes. If the conductance sensor is still surrounded by foam or detects foam, it is possible to use the further countermeasure of introducing fresh water for rinsing the foam away. After introducing fresh water for a certain time, or in a certain quantity, a check is again made to establish whether the conductance sensor is surrounded by foam. If this is the case, further fresh water can be added until the foam is eliminated. As a further test measure, the pump can be started. If it then idles, which can be easily established by measuring the power consumption of the pump and this lasts for a few seconds to a few minutes, there is in fact still foam at the conductance sensor. 
         [0019]    According to a further basic embodiment of the invention, it is possible in a method for operating an aforementioned conductance sensor, or during the measurement of the conductivity in the washing liquid container or liquid, to briefly interrupt the washing or rinsing process, particularly also a spin drying process, in order to carry out the conductance measurement. Particularly in the case of an interruption or for the conductance measurement, the drum can be stopped and then the conductance is measured with the drum stationary. This avoids the liquid being impacted by the drum movement in the washing liquid container so as to produce foam. It is also possible to calm the water in the washing liquid container, which also permits a better and more reliable conductance sensor evaluation. 
         [0020]    It is also possible within the scope of the invention that one of two prescribed safety circuits for the heater can be avoided, because it is possible to determine with the conductance sensor within the framework of the aforementioned water level measurement whether the heater is in the water. This permits a simpler washing machine construction. 
         [0021]    These and further features can be gathered from the claims, description and drawings and individual features, individually or in the form of subcombinations, can be implemented in an embodiment of the invention and in other fields and can represent advantageous, independently protectable constructions for which protection is claimed here. The subdivision of the application into individual sections and the subheadings in no way restrict the general validity of the statements made thereunder. 
         [0022]      FIG. 1  shows a washing machine according to an embodiment of the invention and having a drum  13  containing washing or laundry  14 . Drum  13  is driven by motor  15  with a belt drive. A washing liquid or powder container is located below and surrounds the drum  13  and has an outflow  18 . Said outflow  18  leads to a pump  20 , which conveys water out of the washing liquid container  17 , via an outflow hose  21  from the washing machine  11 . Into the washing liquid container  17  projects a heater  23  in order to heat the water or liquor therein.  FIG. 1  does not show an inflow for fresh water and for the detergent-mixed water. However, in the same way as the washing machine is described in this connection, the inflow can be constructed as is known in the prior art. 
         [0023]    In the embodiment shown, a conductance sensor  24  projects into the washing liquid container  17  close to the heater  23 , as is for example known from US 2006/0191496 A1. The conductance sensor  24  effectively defines a broken line-represented level  25  marking the height up to which it can detect water or foam and further reference will be made thereto hereinafter. The conductance sensor  24  is also connected to a control unit  26 , which can also be connected to the pump  20  and/or heater  23 , particularly for the control thereof or for evaluating the operating state thereof. Motor  15  can also be connected to control unit  26  and both can be controlled by the latter and additionally or alternatively for the detection of its operating state, as described hereinbefore. 
         [0024]    As stated hereinbefore, the conductance sensor  24  can, for example, establish whether water or foam is located above or below the level  25  or whether it is immersed in water. This can in particular be used in impacting the above-described pumping operation. It is also pointed out here that the conductance sensor  24  with level  25  is well below the lowermost point of drum  13 . Thus, a water level can rise well above the conductance sensor  24  or level  25  without reaching the drum  13  and the washing  14  therein and making the latter wet again. Appropriate consideration must be taken of this height difference in connection with the above-described, hysteresis curve-like possibility so that when the water rises above level  25 , the pump  20  is only switched on after a certain time, but always in sufficient time before the water reaches drum  13 . The same applies regarding the lowering of the water below level  25  before pump  20  runs dry during pumping away. 
         [0025]    As the different possible methods have already been described, there is no need to go into detail in this connection here, but are made even clearer in conjunction with  FIG. 1 . 
         [0026]      FIG. 2  shows how it is possible to measure the surface tension of the liquid in which is located the content of drum  13 , particularly the laundry  14 , based on the surfactant concentration. There is a fixed relationship between the same and in particular control unit  26  can draw the indicated conclusions therefrom. 
         [0027]    In a similar way the conductance and surfactant concentration are in a fixed mutual relationship, as shown in  FIG. 3 . 
         [0028]    Finally, in accordance with  FIG. 4 , the conductance can be related to the surface tension in the liquor in drum  13  or washing liquid container  17 . Then for the different surfactants and different surfactant concentration ranges, virtually linear relationships are obtained, namely ranges 1 to 4 in  FIG. 4 . If the surfactant concentration range is known to be, for example a very high surfactant concentration during the washing process, conclusions regarding the surfactant concentrations can be drawn from the liquid conductivity on the basis of the conductance. However, if the surfactant concentration is low, for example when rinsing laundry  14  in drum  13 , the conductance can also be established from the fixed relationship. As the control unit  26  advantageously forms the complete control for the washing machine  11 , it is aware of the given program sequence and therefore also knows whether a washing process or a rinsing process is taking place. The precise nature of the surfactant used need not necessarily be known, because on the basis of a starting value and with a random surfactant the concentration change can be detected. This is adequate for the aforementioned optimization of the washing and rinsing processes. In particular, different curves according to  FIG. 4  can be stored in control unit  26  and used for detection purposes.