The present invention refers to a process for measuring and possibly controlling at least one operational parameter of a washing machine having a washing tank connected to a support frame by at least one adjustable damper.

During the stages of washing and centrifuging, the tank of the washing machine can oscillate due to the unbalanced load of laundry, risking coming into contact with the support frame and generating annoying noises.

A technique currently used for preventing this risk is to check changes in speed of the motor which rotates the washing drum during the distributing stage preceding the centrifuging stage, said changes being measured by tachimetric devices on the motor itself. Depending on the deviation of the rotation speed from its average in one revolution, the washing pro- gramme fixes the maximum acceptable limits for the centrifuging speed. This known technique, which has been in use for many years, has the disadvantage, however, of not being very precise, if the rotation speed exceeds 100 rpm, and not very reliable and repeatable, since it uses long processing times. Equally unsuitable are techniques for detecting imbalance in the load based on measurements of acceleration around one or more axes, since they require a subsequent integration to make the calculation of position.

It is also known to detect imbalance in the load on the basis of measurements of the absolute position in space assumed by the washing tank. Such a technique, however, requires the use of inductive sensors of considerable complexity.

EP 0 878 574 Al describes a method of monitoring the vibrations of the horizontal-axis drum of a washing machine.

An object of the present invention is to obviate the above-mentioned drawbacks of the known art.

This object is achieved thanks to a process for measuring and possibly controlling at least one operational parameter of a washing machine having the features indicated in claim 1 below. Preferred features of the invention are indicated in the dependent claims.

According to the invention, measuring an angle between rotating elements and/or measur- ing the change of said angle in each active rotating damper makes it possible to establish the position in space assumed by the washing tank and to obtain from the latter a series of data relating to the operation of the washing machine.

Examples of parameters which can be measured according to the process of the invention are the load of laundry in the washing tank, the quantity of water fed into the washing tank, the displacement of the tank with respect to a reference vertical axis, the displacement of the tank with respect to a reference horizontal axis, the acceleration/deceleration of the washing tank and, in general, the imbalance of the latter. It goes without saying that, if the above-mentioned geometric or kinetic values deviate from those considered acceptable, the detection of the deviation can activate a control system which brings about the correction thereof.

An advantage of the process of the invention is to be precise, reliable and repeatable even at very high speeds of rotation.

Further advantages and characteristics of the present invention will become clear from the detailed description which follows, provided purely by way of non-limiting example with reference to the attached drawings, in which:

figure 1 is a schematic view of a washing machine in which the process of the in- vention is implemented,

figure 2A is a schematic perspective view of a damper of the washing machine of figure 1 , and

figure 2B is a schematic view in section corresponding to the view of figure 2 A. A washing machine has (fig. 1) a washing tank 10, connected to a support frame 12 on its underside by means of rotating dampers 14, whose number can vary from one to four and is preferably three, and on its upper side by means of spring 15. Inside the tank 10 there is further mounted, in conventional manner, a cylindrical drum 16 rotatable by a motor (not shown) which is coaxial with the axis of the tank 10.

Each rotating damper 14 is made up (figures 2 A and 2B) of an element 18 connected to the frame 12 and an element 20 connected to the tank 10. Element 18 comprises an arm 22 having a distal end articulated to the base of the frame 12 and a proximal end integral with a hollow cylindrical housing 24. Element 20 comprises an arm 26 having a distal end articulated to the tank 10 and a proximal end integral with a cylinder 28, constrained to rotate within the hollow cylindrical housing 24. Between facing surfaces of the parts of elements 18, 20 constrained to rotate with respect to each other - i.e. cylinder 28 and housing 24 which are mounted coaxially around an axis 29 - there is formed an annular gap occupied by a magnetorheological substance 30. This term is intended to signify a ferro- magnetizable powder, whose particles may be suspended in an oil and which is capable of varying its rheological properties, such as its viscosity, depending on its state of magneti- zation.

Cylinder 28 houses windings (not illustrated for reasons of clarity) of a coil supplied by electrical cables 32. By varying the current flow supplied by the latter, it is possible to vary the magnetization of the particles of the ferro-magnetizable powder and thus the viscosity of the substance 30, which will thus oppose more or less resistance to the rotation of the cylinder 28 within the housing 24, thus influencing the rigidity of the damper 14.

Cylinder 28 furthermore houses a sensor 34 - provided with its own electrical supply cables 31 - for sensing the angle of rotation of cylinder 28 with respect to housing 24, so that depending on the angular values measured, the state of magnetization of substance 30 and consequently the rigidity of damper 14 can be controlled. In this connection, it should be noted that, since arms 22, 26 are integral respectively with housing 24 and cylinder 28, the change of angle between the latter will correspond to the change of angle between arms 22, 26.

As already mentioned, the measured values of the above angle of each damper 14 make it possible firstly to control as desired the rigidity of the latter and thus the resistance offered to the displacements of tank 10 in the various stages of operation of the washing machine, so as to avoid contact with the support 12.

Knowing these values and/or their change over time makes it possible furthermore to measure one or more operational parameters of the washing machine and possibly to control them, by taking the necessary corrective actions in a short space of time, because they can be rapidly processed, enabling the washing machine to react immediately to undesired deviations from the desired operating conditions. It is thus possible to measure the displacement of tank 10 with respect to a vertical axis and/or a horizontal axis with the washing machine either empty, or loaded but stationary, with a resulting check of the stress on a gasket on the porthole, and of the distance from the frame 12. It goes without saying, given that the lowering/raising of the tank 10 is a function of the total load, both static and dynamic, that by measuring the oscillation of the tank 10 on starting, it is possible also to measure the load of laundry and, when loading with water is completed, the quantity of the latter that has been loaded. Measuring the oscillations of the tank 10 also enables indirect measurement of the imbalance.

Broadly speaking, it is possible to measure the alignment of the tank 10 with respect to the frame 12 and thus to control it so as to avoid twisting thereof, which would be particularly damaging during the centrifuging stage.

Overall, the measured values of the above-mentioned angles can be used by a control algorithm for the washing machine based preferably on calculation tables and therefore not on double integration. ¹

Naturally, without prejudice to the principle of the invention, the details of realization and the forms of implementation can be extensively varied from the descriptions given purely by way of non-limiting example, without for that reason departing from the scope of the invention as defined in the attached claims. For example, the number and the specific type of rotating dampers used, as well as their constituent parts, such as arms, cylindrical parts etc., can be substantially any. Furthermore, in addition to rotating dampers, a desired num- ber of linear dampers may be used.