Abstract:
The invention relates to a method of operating a dishwasher with a central control unit, by measuring the turbidity of the rinsing liquid and establishing the course of the program as a function of the turbidity of the rinsing liquid. In a pre-rinse operation, measurement values determined by a sensor system are derived from the soiling of the rinsing liquid and supplied to the control unit, which calculates therefrom associated parameters for the further course of the program and establishes the latter correspondingly.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a method of operating a dishwasher with a central control unit, by measuring the turbidity of the rinsing liquid and establishing the course of the program as a function of the turbidity of the rinsing liquid. 
     2. Description of the Related Art 
     Dishwashers currently available on the market normally have a control unit—a program control device, with which a rinse program, which can be made up of the part program steps “Pre-rinse”, “Clean”, “Intermediate Rinse”, “Rinse” and “Dry”, can be operated. For this purpose a number of selection switching means are necessary in order to make it possible for the user to adjust the different rinse programs. This multitude of manually effectable choices does not rule out dishwasher operating errors. 
     Consequently, there has been no lack of attempts to create a dishwasher where it is unlikely for the user to make an error, thereby restricting the dishwasher&#39;s consumption of power and water to the smallest possible measurement. 
     Dishwashers have been created where the dishwasher is set in motion at the start of the program and the parameters to be set for the continuation of the rinse program are set as a function of at least one determined parameter, which is necessary to the continuation of the rinsing operation and is influenced by the same. At the same time, in accordance with a specific development of the method, the degree of soiling, i.e. the turbidity of the rinsing liquid, is measured and the rinse program is established as a function of this turbidity in order to guarantee a fully automatic course of the rinse program and consequently to avoid the operator of the dishwasher making an error. 
     It has been shown that no adequate cleaning can be achieved in this manner with optimized power and water consumption for the various types and quantities of soiling. The dishes can be soiled a lot or a little and it can be easy or difficult to remove this soiling from the dishes. Only fresh or dried-on or burnt-on soiling can be referred to. In addition, the dishwasher can be loaded in the two spray planes or only in one spray plane. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to create a method of operating a dishwasher of the aforementioned type, where the rinse program runs automatically with minimum power and water consumption, and consideration is given to the variable soiling of the dishes according to the degree of soiling and solubility, as well as to an arbitrary loading of the spray plane, and nevertheless an excellent cleaning and drying of the dishes is achieved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic of a dishwasher in accordance with an exemplary embodiment of the present invention; 
         FIG. 2  illustrates a sensor data processing at a dishwasher central control unit; and 
         FIG. 3  illustrates further sensor data process at a dishwasher central control unit. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIG. 1  there is shown a dishwasher having a tub  10 . A circulation pump  12  is provided for supplying liquid to a first spray arm  14  operating in an upper spray plane and a second spray arm  16  operating in a lower spray plane. The pump may supply liquid either simultaneously or separately to each spray arm in an alternating manner. A water drain shaft or inlet shaft  18  supplies liquid to the circulation pump  12  which has outputs connected to the upper and lower spray arms  14  and  16 , respectively. A turbidity sensor  20  is incorporated into the inlet shaft  18  such that the turbidity of the inlet flow into the pump is measured. The dishwasher may also be in communication with programmable memory and logic  25  for controlling the wash and rinse programs of the dishwasher. Fuzzy logic or set  30  may also be incorporated to interlink input and output data and modify changes in the rinse program. 
     As illustrated in  FIG. 2 , in a pre-rinse operation as transmitting the following input values from a sensor system to a control unit:
         a) the current temperature of the rinsing liquid and/or the inlet temperature of the fresh water,   b) the turbidity of the rinsing liquid, separately with alternating operation of the lower spray plane and the upper spray plane or with common operation of the spray planes with a continuously operated spray system,   c) the foam load in the rinsing liquid,   d) the increase in the turbidity and   e) the length of time of the rinsing operation until the increase in the turbidity has achieved the value of zero,       

     The following output values could be derived from the input variables by the central control unit:
         f) a value of the turbidity of the rinsing liquid in %,   g) a value of the particle load in the water in %,   h) a value for the solubility of the soiling of the dishes in %,   i) a value for the necessary cleaning temperature in ° C. and   j) a value for the necessary length of the rinsing operation, and   in that the further course of the program, with reference to the number and parameters of the part program steps, is established by the control unit as a function of these output values.       

     With this development of the method, the rinse program is fully adapted to the actual soiling of the dishes. The volumes of water, the length of rinse time and the rinsing temperatures are established on account of the measured and derived values for the soiling of the dishes and the soiling of the water, and the rinse program is accomplished automatically as a function thereof with reference to minimum power and water consumption and optimum cleaning and drying of the dishes and the necessary part program steps. 
     At the same time it can already be provided that the pre-rinse operation is effected with or without heating-up the rinsing liquid, it being possible to make the heating-up operation a function of the degree of soiling and the solubility of the soiling on the dishes. 
     Depending on the development of the dishwasher, with the spray arms of the lower and upper spray planes being operated in an alternating manner or in a simultaneous manner, clear criteria can be derived on the degree and the solubility of the soiling of the dishes, and in this way, the further course of the rinse program can be accomplished in an automatic manner with reference to the volume of water required, water temperature, length of cleaning operation, cleaning temperature, the necessary measurement of cleansing agent and heating-up of the water with the number of part program steps. 
     With the two spray planes of the dishwasher being operated in an alternating manner, another development provides that a turbidity difference value is derived from the turbidity values of the lower and upper spray plane and this turbidity difference value is compared to preset limit values by the control unit in order to make decisions for the continuation of the rinse program. 
     As shown in  FIG. 3 , consideration of the formation of foam in the rinsing liquid, generated in the rinse program, is achieved in that a measurement for the stability of the pressure of the circulating pump is derived from the measured values for the turbidity and the foam formation in the rinsing liquid, wherein, depending on the water output,
         k) small volumes of water are added,   l) the volume of water is increased up to a maximum value or   m) a complete water change is effected as well as   n) part program steps are repeated, and   o) the filter shaft or the drain shaft is rinsed before the next part program step.       

     The pressure of the circulating pump must remain constant for the clear development of the rinse program. This is provided for with the measures specified. The decisive factor of the new method is a reliable value for the solubility of the soiling of the dishes, which is deduced in that the value for the solubility of the soiling of the dishes is derived from the water temperature of the rinsing liquid and the length of time of the rinse operation until the increase in the turbidity of the rinsing liquid has reached the value zero, there being a low water temperature and a short rinse time with easy solubility and a high temperature and a long rinse time with difficult solubility, and in that these values are compared to preset limit values and, as a function therefrom, the necessary further part programs steps are established. 
     The necessary cleaning temperature and length of cleaning operation in the following part program steps can be derived from the turbidity of the rinsing liquid and the solubility of the soiling of the dishes. At the same time, it is provided, on the one hand, that the cleaning temperature for the rinsing liquid in the further part program steps is established as a function of the turbidity of the rinsing liquid and of the determined solubility of the soiling of the dishes, a low cleaning temperature for the rinsing liquid being selected for low turbidity and easy solubility and a high cleaning temperature for the rinsing liquid being selected for high turbidity and difficult solubility, and on the other hand, that a short cleaning operation is selected for low turbidity of the rinsing liquid and easy solubility of the soiling of the dishes and a long cleaning operation is selected for high turbidity of the rinsing liquid and difficult solubility of the soiling of the dishes. 
     In this case, the length of time of the cleaning operation and/or the cleaning temperature is (are) preferably continuously controlled between a minimum value and a maximum value as a function of the turbidity of the rinsing liquid and of the solubility of the soiling of the dishes. 
     The control costs in the central control unit can be kept down by using a fuzzy set in the central control unit for deriving the output values from the input values. 
     If, at the same time, it is also provided that the fuzzy rules, i.e. the logical interlinking of the individual linguistic terms, can be freely programmed in a freely programmable memory in order to adapt the fuzzy set to changes in the rinse program of the dishwasher, the course of the program can then be adapted easily to new conditions. 
     The course of the program can also be adapted by modifying the access conditions of the fuzzy inputs and/or the output conditions of the fuzzy outputs or of the linguistic terms of the fuzzy outputs.