EP0335790A1 - Balance detection means in the washing machines - Google Patents

Abstract

Washing machine having the speed of the drum drive motor (11) under the servo-control of a nominal value supplied by a programmer (10), such as a microprocessor. The servo-control error signal is also used to detect unbalances in the drum, in order to slow the latter when this error signal exceeds a limit value. The error signal used for detecting unbalances or the limit value has a value which is a function of the inertia of the laundry in the drum before spinning. <IMAGE>

Description

The invention relates to means for detecting unbalances in the drum of a washing machine.

In European patent n ° 91 336 in the name of the applicant, a washing machine has been described having a servo-control of the speed of the drum drive motor to a setpoint supplied by a programmer in which the unbalances are detected by the signal d 'error of the enslavement. By error signal is meant the difference between the actual speed of rotation of the drum and the set speed. The unbalance is detected, for example, when the drum is accelerated before spinning.

Such an unbalance detection means is inexpensive because the same signal is used for this detection and for speed regulation.

The error signal is compared with a limit value and if it exceeds this limit the drum is slowed down in order to prevent the imbalances thus detected from causing harmful consequences for the various parts of the machine when the drum rotates at high speed. speed.

Due to the seriousness of the risks run by the machine in the event of unbalances, it is understood that the method of detecting unbalances must be particularly reliable.

Although the reliability of the unbalance detection described in the prior patent is satisfactory, it has however been found that in certain cases, which are infrequent, the detection could be faulted.

The invention overcomes this drawback.

It is based on the discovery that detection faults occur when the load of laundry introduced into the drum has a large rotational inertia. Such a situation arises for example for a large load of laundry, for example 3.5 kg of cotton with terry towels mass 2.5 kg (absorbing a lot of water) which can cause imbalance.

It has thus been found that the error signal is lower the greater the inertia.

The washing machine according to the invention is characterized in that it comprises a means for measuring the inertia of the laundry on which the error signal and / or the limit value are made to depend. If the limit value is varied, the latter will be lower the higher the inertia; if the limit value remains constant, the measured error signal is increased, compared to this limit, as a function of the inertia.

The measurement of the inertia can be carried out for example as described in the French patent n ° 85 02969 also in the name of the plaintiff, that is to say by measurement of the driving torque of the drum with determined acceleration, in particular constant, of the latter. When the electric motor for driving the drum is of the universal type, the driving torque is measured by determining the intensity of the electric current passing through this motor.

The measurement of the inertia used to modify the error signal or the limit value ε _M is generally carried out just before spinning. For this measurement it is preferable that the speed of rotation of the drum is limited so as not to reach the speeds for which the machine enters into resonance. A speed limit of 150 revolutions per minute has proved acceptable for this measurement for a machine whose main critical speed is 180 rpm.

• - la figure 1 est un schéma montrant un moteur d'entraînement de tambour et son circuit de commande,
• - les figures 2_a et 2_b sont des diagrammes de variation de la vitesse de rotation du tambour d'un lave-linge en cas de balourds, et
• - les figures 3 et 4 sont des diagrammes illustrant le fonctionnement du moyen de mesure du moment d'inertie du linge contenu dans le tambour.

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:

• FIG. 1 is a diagram showing a drum drive motor and its control circuit,
• FIGS. 2 _a and 2 _b are diagrams of variation of the speed of rotation of the drum of a washing machine in the event of unbalances, and
• - Figures 3 and 4 are diagrams illustrating the operation of the means of measuring the moment of inertia of the laundry contained in the drum.

The embodiment of the invention relates to a washing machine for domestic use with a rotating drum with a horizontal axis. This drum, in a conventional manner, is cylindrical in shape with perforated walls to allow the water or the mixture of water and detergent present in the tank, to soak the laundry. The operation is fully automatic, that is to say that the user does not have to intervene between the start and the end of the operation. The various operations, controlled by a programmer, are, in general, prewash, washing, one or more rinses, and spinning.

The control is provided by a microprocessor 10 (Figure 1). The latter imposes on the universal motor 11 for driving the drum a set speed. To this end, the microprocessor 10 acts on a circuit 12 for controlling the conduction time of a switch 13, such as a triac, in series with the universal motor 11 and the AC power source 14. This circuit with switch 13 is of the phase-cutting type, that is to say that at each alternation of the alternating current produced by the generator 14 the switch 13 is open for a time which is a function of the desired speed for the engine 11.

A tachometer generator 15 is attached to the motor shaft 11, which supplies a signal representing the actual speed of this motor. This signal is applied to an input 10₁ of the microprocessor 10 to be compared to the set speed. The difference, called error signal ε, between the actual speed and the set speed is used to regulate the speed. Speed regulation is called closed loop.

As described in European patent 91 336, the error signal ε is also used to detect unbalances and to slow down the rotation of the drum if this error signal, and therefore the unbalance, exceeds a predetermined limit value.

To this end, the microprocessor 10 is programmed to command a reduction in the speed of the drum when the error signal exceeds a limit value ε _M. This unbalance detection is only used when starting the spin, that is to say when you start increasing the rotation speed of the drum. If, in this case, the error signal ε exceeds the limit value ε _M, the speed of rotation of the drum is reduced to a speed corresponding to that for washing and the drum is left to rotate for a few seconds at this speed so that the laundry undergoes "steam release". At the end of this operation, the acceleration of the drum is started again, the imbalance having a high probability of having disappeared. Otherwise the drum is slowed down again. If after several attempts (for example three) to accelerate the unbalance remains, the rotation is stopped completely.

As already indicated above, it has been observed that in certain cases, despite the presence of an annoying unbalance, the error signal does not exceed the prescribed limit value. The inventors have discovered that this malfunction occurs especially when the laundry in the drum has a large rotational inertia relative to the axis of this drum.

The invention therefore consists in modifying the signal ε or the limit value ε _M as a function of this inertia.

The dependence of the signal ε on the moment of inertia of rotation of the laundry with respect to the axis of rotation of the drum can be explained as follows:

During acceleration, when the rotation speed of the drum changes from a value ω₁ to a slightly higher value ω₂, the kinetic energy supplied compensates for the resistance torque due to unbalance. We can therefore write:
(1) ½ J (ω ₂² - ω ₁²) = C Δ ϑ

In this formula J is the moment of inertia of rotation of the linen, C the torque due to the unbalance and Δϑ the angle by which the drum turned during the period during which the speed increased from ω ₁ to ω ₂.

The difference between ω₂ and ω₁ being, by hypothesis, small we can write:
(2) J ω _m Δω = CΔϑ

In this formula Δω = ω₂ -ω₁, and ω _m is the average value of ω between ω₁ and ω₂.

From where :

From formula (3) above we deduce that the speed variations Δω due to unbalance decrease when the inertia increases. In other words, the higher the inertia, the less the variations Δω in speed, which explains the observed defect, that is to say: despite the presence of very strong unbalances for the strong inertias the error signal ε does not exceed the prescribed limit ε _M.

It will also be noted that, taking account of the formula (3) above, the error signal ε decreases when the speed increases. It is therefore preferable to measure the unbalance for the speeds which are not too high, that is to say at the start of the acceleration, between the speed for which the laundry is pressed against the wall of the drum and the critical speed. .

In formula (1) above, neither the energy supplied to the drum by the motor, nor friction, nor the effect of the regulation of the drive motor have been taken into account. However, it has been found that, despite this, the speed differences depend, as in formula (3) above, on the inertia and the average speed.

It is also recalled that the amplitude of the error signal depends, as described in European patent 91 336, on the precision of the regulation. However, the smoothing effect brought about by the increase in inertia and / or in the average speed can be seen in the error signal regardless of the precision of the regulation.

The variation in the speed of rotation V (or ω) of the drum as a function of time t is shown in FIGS. 2 _a and 2 _b . In these figures the speed V₁ is the rotation speed of the drum for washing, and V₂the spin speed. The curve 20 in FIG. 2 _a corresponds to a higher inertia of the linen than in the case of the curve 24 in FIG. 2 _b , the unbalances being identical. In both cases we see that at the start of the acceleration the oscillations 22 have a greater amplitude than the oscillations 23 at the end of the acceleration.

To take account of the inertia, the microprocessor is programmed to divide the limit value ε _M by a quantity which increases with the value J of the inertia. As a variant, the signal ε used for the detection of unbalances is multiplied by the value J of the inertia or by a quantity which varies like this inertia.

In a simplified embodiment, two distinct values are assigned to ε _M : a first value when the inertia of rotation of the laundry is less than a value J₁ and a second value, less than the first, when the inertia of the laundry exceeds the value J₁ . We can also assign to ε _M several values depending on whether the inertia is less than a first value J₁, between this first value and a second value J₂, etc.

If the limit value ε _M is constant, in an analogous manner it is not essential that the multiplying coefficient of the signal ε varies continuously as a function of the inertia. For example, the multiplying coefficient may have a first value for the inertias less than J₁ and a second value for the inertias greater than J₁.

In the preferred embodiment, the microprocessor comprises, for the detection of prohibitive unbalances, a table for converting the signal ε as a function of the inertia J or a table for converting the limit ε _M as a function of this inertia J.

+ C_f + C_b sinωtThe moment of inertia J of the wet linen is measured before the drum rotates at its critical speed, that is to say 180 rpm in the example. For this measurement, the means described in French patent 85 02969 published under No. 2,577,949 can be used. One can also use the following formula: (4) C _e = (J + J₀) $\frac{\text{from}}{\text{dt}}$

+ C _f + C _b sinωt

l'accélération et C_b le couple dû au balourd.In this formula C _e is the drive torque of the drum, i.e. the torque provided by the universal motor, C _f is the friction torque due to the rotation of the drum, J₀ the moment of inertia of the drum relative to its axis of rotation, ω the speed of rotation of this drum, $\frac{\text{from}}{\text{dt}}$

acceleration and C _b the torque due to unbalance.

From formula (4) above we deduce:

peut être imposée par l'asservissement; de préférence elle est égale à une constante connue non nulle. Dans ces conditions le moment d'inertie J du linge dépend alors seulement du couple C_e d'entraînement du tambour et de la composante oscillatoire C_bsin ω t dûe au balourd. Mais comme la valeur moyenne de cette composante oscillatoire est nulle, elle ne modifie pas la valeur moyenne du moment d'inertie. Ainsi J ne dépend que du seul paramètre C_e. Pour être certain que la valeur moyenne de la composante oscillatoire C_b sin ω t soit nulle il est préférable que la mesure soit effectuée pendant un nombre entier de tours du tambour.In this formula J₀ and C _f are in principle constants. C _f can however vary from one machine to another even if the machines come from the same production line. If this is the case, the method of measuring C _f described below can be used. Acceleration $\frac{\text{from}}{\text{dt}}$

may be imposed by slavery; preferably it is equal to a known non-zero constant. Under these conditions the moment of inertia J of the linen then only depends on the torque C _e of driving the drum and on the oscillatory component C _b sin ω t due to the unbalance. But since the mean value of this oscillating component is zero, it does not not modify the mean value of the moment of inertia. Thus J depends only on the single parameter C _e . To be sure that the mean value of the oscillatory component C _b sin ω t is zero, it is preferable that the measurement be made during an integer number of revolutions of the drum.

As the drive motor is of the universal type and as the supply voltage is constant, the drive torque C _e is related to the intensity I of the electric current flowing through the motor by the following relationship:
(6) C _e = K (I - I₀)

In this formula K and I₀ are constants.

If the acceleration imposed on the drum is constant, the moment of inertia J of the laundry only depends on the intensity of the electric current passing through the universal motor. It will be noted that due to the oscillatory component of the unbalance, the moment of inertia J is not directly a function of the instantaneous intensity of the electric current passing through the motor, but of the mean value of the effective intensity.

Under these conditions before the acceleration to reach the spin speed, the drum is subjected to setpoint speed variations which are represented by the diagram in FIG. 3 which shows the variations as a function of time t of the setpoint speed of rotation. V (or ω) of the drum. Between the instants t₁ and t₂ the drum is rotated at a slightly increasing speed so that it reaches, at time t₂, a speed of rotation of the order of 50 to 80 revolutions per minute. This first phase aims to distribute the laundry uniformly in the drum.

Between the instants t₂ and t₃ the drum rotates at the constant speed V₂₃ of the order of 50 to 80 revolutions per minute. The speeds of 50 to 80 revolutions per minute which are given above by way of example are chosen in such a way that the distribution of the laundry is not changed. These speeds depend on the diameter of the drum; they decrease if the diameter increases.

Between the instants t₂ and t₃, the acceleration being zero, the driving torque is equal to the friction torque C _f1 . The current absorbed by the motor thus has a relatively low effective intensity I _V23 , as shown in FIG. 4 which represents the variations of the effective intensity I _eff as a function of time t.

Between the instants t₃ and t₄ the rotation of the drum is accelerated with a constant and determined value of acceleration. The drive torque has a significantly higher value. It naturally follows that the effective intensity I _V34 (FIG. 4) of the current absorbed by the motor is higher. Then, between instants t₄ and t₅, the speed of rotation of the drum is kept constant at a value of the order of 150 to 200 revolutions per minute. In this last phase the driving torque is only equal to the torque necessary to overcome friction.

The speed V₄₅ must be less than the main critical speed of the machine, generally around 200 revolutions per minute. This critical speed is that for which the most significant vibrational resonance of the suspended assembly formed by the tank, the drive motor and the drum occurs.

Taking into account formulas (5) and (6) above, we deduce the value of the moment of inertia:

sont des constantes imposées lors de la construction de la machine. I₃₄ est mesuré par exemple en déterminant la tension aux bornes d'une résistance en série avec le moteur. On peut aussi mesurer l'intensité I₃₄ en déterminant l'angle de phase moyen de conduction d'un interrupteur commandé quand (comme dans l'exemple) on a affaire à une régulation à découpage de phase. C_f34 n'est pas mesurable directement; dans le cas présent on estime que C_f34 est la moyenne arithmétique entre le couple de frottement C_f23, entre les instants t₂ et t₃, et le couple de frottement C_f45 entre les instants t₄ et t₅.In this formula I₃₄ is the effective intensity of the electric current passing through the drum drive motor between times t₃ and t₄ and C _f34 is the friction torque also between times t₃ and t₄. K, I₀, J₀ and the acceleration $\frac{\text{from}}{\text{dt}}$

are constants imposed during the construction of the machine. I₃₄ is measured for example in determining the voltage across a resistor in series with the motor. We can also measure the intensity I₃₄ by determining the average phase angle of conduction of a controlled switch when (as in the example) we are dealing with a phase-cut regulation. C _f34 is not directly measurable; in the present case it is estimated that C _f34 is the arithmetic mean between the friction couple C _f23 , between the instants t₂ and t₃, and the friction couple C _f45 between the instants t₄ and t₅.

C _f23 and C _f45 are easily measurable by the intensities I₂₃ and I₄₅ of the currents flowing through the universal motor between the times t respectivement and t₃ and t₄ and t₅ respectively.

As already described in European patent 91 336, it is preferable that the precision of the servo-control be limited so that the error signal has a measurable value. For example, the accuracy of the speed measurement is around 3 revolutions per minute.

For the limit value, for example: when the inertia of the wet laundry corresponds to a mass of 3 kg brought (by calculation) to the periphery of the basket, the limit value ε _M is around 20 revolutions per minute. When this inertia of linen corresponds to a mass of 9 kg brought to the periphery of the basket, the limit value is of the order of 7 revolutions per minute.

Claims (13)

1. Washing machine comprising a servo-control of the speed of the drum drive motor to a setpoint supplied by a programmer, the error signal (ε) of the servo-control being also used to detect imbalances in the drum , in order to slow down the drum when the error signal (ε) exceeds a limit value (ε _M ), characterized in that the error signal used for the detection of unbalance and / or the limit value (ε _M ) is present a value which is a function of the inertia (J) of the laundry in the drum before spinning. 2. Machine according to claim 1, characterized in that the limit value is reduced (ε _M ) when the inertia of the laundry increases. 3. Machine according to claim 1, characterized in that the error signal used for the detection of unbalances is increased when the inertia of the laundry increases. 4. Machine according to any one of the preceding claims, characterized in that it comprises a microprocessor (10) with in memory a table of correspondence between, on the one hand, the error signal used for the detection of imbalances and / or the limit value (ε _M ) and, on the other hand, the laundry moment of inertia values. 5. Machine according to any one of the preceding claims, characterized in that for measuring the moment of inertia of the laundry with respect to the axis of rotation of the drum, it comprises means for measuring the driving torque of the drum at determined acceleration, preferably constant and not zero, of this drum. 6. Machine according to claim 5, characterized in that said driving torque of the drum during an integer number of turns of the latter. 7. Machine according to claim 5 or 6, characterized in that, for the measurement of the moment of inertia, the drum is driven at a speed lower than that for which resonances occur. 8. Machine according to claim 7, characterized in that for the measurement of the moment of inertia the drum drive speed is at most 150 to 200 revolutions per minute. 9. Machine according to any one of claims 5 to 8, characterized in that, the drum being driven by an electric motor of the universal type, for measuring the drive torque it includes means for measuring the intensity of the electric current going through the engine. 10. Machine according to claim 5, characterized in that it comprises a means for rotating the drum, before rotation at constant acceleration, at slightly increasing speed in order to distribute the laundry uniformly in the drum. 11. Machine according to claim 5, characterized in that it comprises a means for rotating the drum, before its rotation at constant acceleration, at constant speed, this drum also being driven at another constant speed after the rotation at constant acceleration , the drive torques being determined during these two rotations at constant speed, and a calculation means is provided for carrying out an average between these two couples, this average representing the friction torque. 12. Washing machine comprising a servo-control of the speed of the drum drive motor to a setpoint supplied by a programmer, the servo-control error signal also being used for the detection of unbalances, characterized in that 'It includes means for making the error signal used for detecting unbalances dependent on the moment of inertia of the laundry in the drum. 13. Machine according to any one of claims previous, characterized in that the moment of inertia of the laundry is measured after washing and just before spinning.

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