Method for controlling a washing machine

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 re...

AI Technical Summary

Benefits of technology

[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.

Problems solved by technology

However the possibilities for further processing or using these measured values as described therein are limited.

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