EP0410827B1 - Washing machine or dryer with means for automatically determining the weight of the laundry - Google Patents

Description

The invention relates to a method for determining the load of laundry in a washing machine or dryer. It applies in particular to a washing machine or dryer with rotating drum driven by an electric motor preferably of the universal type and in which the load of laundry is determined automatically as a function of the inertia of the latter. relative to the axis of rotation of the drum.

It is known that in domestic washing machines it is preferable that the volumes of water introduced into the machine as well as the quantity of detergent and other parameters of the various operating phases of the washing machine depend on the load of laundry in the drum. The operation of the dryers also depends on the load of laundry.

Various means of automatic load determination have already been proposed. The invention relates to an improvement to the means described in EP-A-0 143 685 in which the load of laundry is measured by the moment of inertia L of the laundry around the axis of rotation of the drum. This moment of inertia is determined from the drive torque of the determined acceleration drum. This torque is measured by the intensity of the electric current flowing through the universal motor.

According to the invention, the universal drum drive motor is supplied with alternating current and its speed is determined by a phase control command using a processor and this processor makes it possible to measure the moment of inertia of the laundry from the value of the phase angle without the need to provide a particular means of measuring the intensity of the electric current.

The phase angle generally depends on the value V _S of the supply voltage supplied to the drum drive motor. However, this voltage can vary within wide proportions, between 187 and 242 volts, that is to say that this value VS is known with a margin of uncertainty which introduces a sometimes unacceptable inaccuracy in the measurement of the load of linen.

To remedy this drawback, a means is provided for measuring the supply voltage and for using this measurement in the calculation of the load of laundry by the processor.

To this end, a method for determining the load of laundry in a washing machine or dryer is defined by claim 1.

Preferably the measurement is carried out without the use of an additional means such as a voltmeter, using only the data already available in the processor. For this purpose the processor requires that, for a determined time, the phase angle has a fixed value and, during this period, the speed of rotation of the motor is determined, the voltage being calculated from the angle of prefixed phase and the speed of rotation thus measured.

The relationship between the supply voltage and the phase angle and speed depends on other parameters which, in principle, do not vary. However, some of them, in particular the friction torque which opposes the rotation of the drum, may have values which vary over time, that is to say with the aging of the machine. To take account of this variation, in one embodiment, the processor is stored in a table indicating the variations, as a function of the number of operating cycles of the machine, of the constant parameters in the relationship between the supply voltage and the phase angle and speed. For example, each time the machine is used, a counter is incremented by one so as to vary the constant (s) in said relation.

• la figure 1 est un schéma montrant un moteur d'entraînement de tambour de lave-linge avec son circuit de commande, et
• les figures 2 et 3 sont des diagrammes illustrant le fonctionnement d'une commande de lave-linge selon l'invention.

Other characteristics and advantages of the invention will appear with the description of some of its embodiments, this being carried out with reference to the attached drawings in which:

• Figure 1 is a diagram showing a washing machine drum drive motor with its circuit command, and
• Figures 2 and 3 are diagrams illustrating the operation of a washing machine control according to the invention.

In the example the washing machine (not shown as a whole) is of the domestic type with a washing drum with a perforated cylindrical wall rotating around a horizontal axis inside a tank.

The electric motor 10 (FIG. 1) for driving the drum is of the universal type. It is supplied with alternating current 11, for example at the frequency of 50 Hz from the network, by means of a controlled switch 12 such as a triac.

For the control of the switch 12, and therefore of the motor 10, a microprocessor 13 is provided, connected to the control electrode of the triac 12 by means of an interface circuit 14.

The microprocessor 13 imposes on the motor 10 a set speed dependent on a program prerecorded in its memory. This microprocessor also constitutes the comparator for speed regulation. To this end, it has an input 13₁ to which is applied the output signal of a tachometer generator 15 driven by the motor 10.

The microprocessor 13 controls the angle ϑ (FIG. 2) of opening of the triac 12 at each alternation of the alternating signal 11, that is to say the duration during which this switch 12 is conductive during each period of this signal 11.

On the diagram of FIG. 2, the opening angle ϑ is shown on the abscissa and the ordinate is the alternating signal 11. During a alternation of the signal 11, that is to say for phase angles ϑ between 0 and ¶ radians, the triac is open, that is to say non-conductive, between angles 0 and ϑ and conductive between angles ϑ and ¶. It is the microprocessor 13 which provides the closing control pulse for the triac 12.

This phase angle ϑ, which is determined by the microprocessor 13, is used for the measurement of the moment of inertia L of the laundry in the drum, that is to say for the measurement of the laundry load.

   Dans cette formule C est le couple moteur, L le moment d'inertie du linge par rapport à l'axe du tambour, J le moment d'inertie du tambour par rapport à son axe de rotation, d ω /dt l'accélération (ou décélération) de la rotation du tambour et C_R le couple résistant qu'oppose le tambour.We start from the following formula: $$\text{C = (L + J)}\frac{\text{from}}{\text{dt}}{\text{+ C}}_{\text{R}}$$

In this formula C is the engine torque, L the moment of inertia of the laundry with respect to the axis of the drum, J the moment of inertia of the drum with respect to its axis of rotation, d ω / dt the acceleration ( or deceleration) of the rotation of the drum and C _R the resisting torque opposed by the drum.

   K étant une constante propre au moteur et I l'intensité du courant électrique qui le traverse.For a universal motor, the motor torque is proportional to the intensity of the electric current flowing through it, that is to say: $$\text{C = KI}$$

K being a constant specific to the motor and I the intensity of the electric current which crosses it.

   K′ étant une constante.In addition, we know that the counter-electromotive force E of the universal motor is proportional to its speed of rotation; we can therefore write: $$\text{E = K′ω}$$

K ′ being a constant.

   De cette formule on déduit : $$\text{U = E + ZI = K'ω + ZI = K'ω +}\frac{\text{ZC}}{\text{K}}$$

   Or, la tension U fournie au moteur est (figure 2) fonction de l'angle ϑ , c'est-à-dire : $${\text{U = V}}_{\text{S}}\text{f( ϑ) = K'ω +}\frac{\text{ZC}}{\text{K}}$$

   V_S étant l'amplitude maximum de la tension 11.We also know that the voltage U across the terminals of the motor is linked to the counter-electromotive force E, to the impedance Z presented by this motor and to the intensity I by the following relation: $$\text{U = E + ZI}$$

From this formula we deduce: $$\text{U = E + ZI = K'ω + ZI = K'ω +}\frac{\text{ZC}}{\text{K}}$$

However, the voltage U supplied to the motor is (FIG. 2) a function of the angle ϑ, that is to say: $${\text{U = V}}_{\text{S}}\text{f (ϑ) = K'ω +}\frac{\text{ZC}}{\text{K}}$$

V _S being the maximum amplitude of the voltage 11.

   De la formule (7) ci-dessus on peut déduire, selon l'invention, la valeur L du moment d'inertie du linge. Toutefois on voit que cette formule fait appel à la valeur V_S de la tension du secteur, laquelle peut être variable. C'est pourquoion préfère mesurer la tension V_S, de préférence par une méthode indirecte ne faisant pas appel à un appareil de mesure spécifique.From formulas (5) and (6) above we deduce:

From formula (7) above, it is possible to deduce, according to the invention, the value L of the moment of inertia of the laundry. However, it can be seen that this formula uses the value V _S of the mains voltage, which can be variable. This is why it prefers to measure the voltage V _S , preferably by an indirect method which does not use a specific measuring device.

In a first embodiment, the microprocessor 13 is programmed to impose, during successive periods 20 and 21 of durations t₁ and t₂ (FIG. 3), values determined at the phase angle ϑ. During the first period 20 of duration t₁, the phase angle is equal to ϑ ₁. During the second period 21 of duration t₂, the phase angle is equal to another determined value ϑ ₂.

Each value of the phase angle ϑ corresponds to a speed of rotation ω of the drum which is measured by the tachometer 15.

During each of periods 20 and 21, of durations respectively t₁ and t₂, the speed of rotation of the drum is constant, that is to say that the acceleration dω / dt is zero.

   Lors de la période 21 la formule (7) s'écrit de même :

   Des formules (8) et (9) ci-dessus on déduit par soustraction : $${\text{V}}_{\text{S}}\text{[ f( ϑ ₂)-f( ϑ ₁)] = K′(ω ₂ - ω ₁)}$$

   Soit :

   Ainsi V_S peut être calculé dans le microprocesseur en fonction de ϑ ₂ et ϑ ₁ qui sont fixés, et de ω ₂ et ω ₁ qui sont mesurés.Thus during period 20 the above formula (7) is written:

During period 21 the formula (7) is written in the same way:

From formulas (8) and (9) above we deduce by subtraction: $${\text{V}}_{\text{S}}\text{[f (ϑ ₂) -f (ϑ ₁)] = K ′ (ω ₂ - ω ₁)}$$

Is :

Thus V _S can be calculated in the microprocessor as a function of ϑ ₂ and ϑ ₁ which are fixed, and of ω ₂ and ω ₁ which are measured.

   K₁ étant une constante.The calculation is facilitated if we assume that f (ϑ) is proportional to ϑ, that is to say: $$\text{f (ϑ) = K₁ ϑ}$$

K₁ being a constant.

   Dans les calculs ci-dessus on a supposé que le couple résistant C_R a la même valeur à la vitesse ω ₁ qu'à la vitesse ω ₂. Cette hypothèse n'est pas exacte en toute rigueur. Toutefois elle est vérifiée sans altérer la précision de la mesure si les valeurs ϑ₁ et ϑ₂ ne sont pas trop différentes l'une de l'autre, c'est-à-dire si ces valeurs sont voisines.In that case :

In the calculations above it has been assumed that the resisting torque C _R has the same value at speed ω ₁ as at speed ω ₂. This assumption is not correct in all rigor. However it is verified without altering the precision of the measurement if the values ϑ₁ and ϑ₂ are not too different from each other, that is to say if these values are close.

By way of example, the values of ϑ₁ and ϑ₂ are chosen so that during period 20 the drum rotates at a speed of the order of 200 revolutions per minute and during period 21 the drum rotates at a speed of the order of 400 revolutions per minute. In this example, periods 20 and 21 have the same duration of approximately 18 seconds.

   dω₁/dt étant l'accélération correspondant à la rampe 22 et dω₂/dt l'accélération correspondant à la rampe 23. Ces accélérations s'effectuent, dans l'exemple, entre les vitesses de 200 et 400 tours par minute.In the embodiment shown in FIG. 3 the periods 20 and 21 are followed by periods 22 and 23 of durations respectively t₃ and t₄ during which the accelerations of the determined value are imposed. During each of these acceleration ramps, the phase angles ϑ′₁ and ϑ′₂ are determined for the same speed, which makes it possible to determine L from the following formula:

dω₁ / dt being the acceleration corresponding to the ramp 22 and dω₂ / dt the acceleration corresponding to the ramp 23. These accelerations are carried out, in the example, between the speeds of 200 and 400 revolutions per minute.

The value V _S found in formula (14) above is taken from the preliminary calculation carried out with formula (11) or (13). This value V _S can also be measured directly.

   Le terme ZC_R/K est considéré comme constant, car la vitesse de rotation ω ₃ s'écarte relativement peu d'une valeur moyenne prédéterminée.In another embodiment, instead of providing for two successive phases 20 and 21 during which phase angles of different values are imposed, only one period of duration t₅ (not shown) is provided during which an angle is imposed phase ϑ₃ and the speed ω₃ is measured using the tachometer 15. Thus the value V _S is determined by the following formula:

The term ZC _R / K is considered to be constant, since the speed of rotation ω ₃ deviates relatively little from a predetermined average value.

   Dans cette formule :

   En mémoire du microprocesseur on introduit une table de correspondance entre ω ₃ et V_S ce qui permet de déterminer immédiatement V_S à partir de la valeur ω ₃.This term ZC _R / K is introduced into the microprocessor read-only memory during the manufacture of the washing machine control. Thus the voltage V _S is determined by the following relation:

In this formula:

In the memory of the microprocessor, a correspondence table between ω ₃ and V _{S is introduced} , which makes it possible to immediately determine V _S from the value ω ₃.

The resistant torque C _R , mainly due to friction, varies depending on the number of uses, or operating cycles, of the washing machine.

The law of variation of C _R as a function of this number of cycles can be determined experimentally and a correspondence table between the number of cycles and the value of the torque C _R is introduced into the memory of the microprocessor.

The number of cycles carried out by the machine is memorized for example in a memory of the EEPROM type associated with the microprocessor, this number being incremented by one after each operating cycle, that is to say after having been detected, on the one hand, switching on and, on the other hand, executing the last step of the washing machine's operating program. It is of course possible to store the number of cycles by another means such as a counter of the electromechanical type.

Claims (9)

1. Process for determining the laundry load in the drum of a washing machine or dryer, the load being determined by the value of the moment of inertia (L) of the laundry with respect to the drum, the drum being driven by a motor (10) of the universal type supplied with alternating current (12) and its speed being prescribed through a command with phase control by virtue of a microprocessor (13), characterized in that the microprocessor determining the moment of inertia (L) from the value (ϑ) of the phase angle and from the value (Vs) of the supply voltage, in order to measure the said supply voltage (Vs), at the start of operation, a determined value (ϑ₃) is prescribed for the phase angle and the speed of rotation (ω₃) of the drum is determined with the aid of a tachometric generator (15) driven by the motor (10), the microprocessor (13) determining the supply voltage (Vs) from the prescribed value (ϑ₃) of the phase angle and from the measured value (ω₃) of the speed.
2. Process according to Claim 1, characterized in that the means for measuring the speed is connected to an input (13₁) of the processor (13) so as to regulate the speed of the motor (10) as a function of a program in the memory of the processor.
3. Process according to Claim 1 or 2, characterized in that the voltage (V_s) is determined from the following relation:

   

   K' and K'' being constants, f(ϑ₃) a determined function of the preset phase angle ϑ₃, and ω₃ the speed of rotation of the drum for the phase angle ϑ₃.
4. Process according to Claim 3, characterized in that it includes a means for storing the number of operating cycles of the machine and for making the value of the parameter K'' depend on this number.
5. Process according to Claim 1, characterized in that a second step is prescribed in the course of which the phase angle keeps a constant value (ϑ₂) different from the first (ϑ₁) and the speed of rotation (ω₂) of the drum is measured, the voltage (V_s) being determined from the prescribed phase angles (ϑ₂, ϑ₁) and from the measured speeds (ω₂ and ω₁) during these two steps.
6. Process according to Claim 5, characterized in that the voltage (V_s) is determined from the following relation:

   

   K' and K'' being constants.
7. Process according to Claim 5 or 6, characterized in that the values (ϑ₁ and ϑ₂) of the phase angles are such that in the course of one step the speed (ω₁) is of the order of 200 revolutions per minute and in the course of the other step the speed of rotation of the drum is of the order of 400 revolutions per minute.
8. Process according to any one of the preceding claims, characterized in that the processor (13) determines the moment of inertia (L) from the phase angle (ϑ) and from the voltage (V_s) through the following relation: $${\text{V}}_{\text{s}}\text{f(ϑ) = K'ω+}\frac{\text{ZC}}{\text{K }}\text{= K'ω+}\frac{\text{Z}}{\text{K}}\text{(L+J)}\frac{\text{dω}}{\text{ K}}\text{D}$$

   

   ω being the speed of rotation of the drum, K' and K constants, Z the impedance of the motor, J the moment of inertia of the drum and C_R the resistive torque opposed by the drum.
9. Process according to any one of the preceding claims, characterized in that, in order to determine the moment of inertia, the drum is made to rotate successively (22, 23) according to two different values of acceleration and in that the said moment of inertia (L) is calculated from a difference between, firstly, a measurement made during the first acceleration and, secondly, a measurement made during the second acceleration.

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