EP0468862B1 - Control method of the rotational speed of the drum of a centrifuging machine as function of imbalance and machine for the use of this method - Google Patents

Description

The present invention firstly relates to a method for controlling the speed of rotation of the drum of a centrifugal wringing machine, as a function of the unbalance of the laundry in the drum, said machine being provided with an alternating current motor. for driving said drum and a device for controlling the speed of said motor by adjusting the angle of passage of the current passing through it.

Such a method makes it possible to take account of the unbalance, in particular so as not to control a spin phase at too high a centrifugation speed in the event of significant unbalance. Indeed, such a spin risks causing damage when the drum rotation frequency is close to one of the mechanical resonance frequencies of the machine.

In known manner, when a significant unbalance has been detected, in principle one begins by trying to reduce it either by stopping the drum, or by slowing it down enough so that the laundry is otherwise distributed inside the drum. If after several attempts of this kind, the unbalance is not reduced, one proceeds nevertheless to the spin, but at a reduced speed, sufficiently low to be compatible with the value of the unbalance. If this is much too large to be compatible with a spin, even at reduced speed, the machine is left to stand, if necessary by setting off an alarm so that the user comes manually to distribute the laundry correctly.

Processes of the type defined above are already known, in particular by applications GB-A-2 102 985, FR-A-2 524 020, GB-A-2 124 662 and FR-A-2 629 484. In the methods described in these documents, the unbalance detection involves either stress sensors, to measure the mechanical stresses exerted on certain machine components in the event of unbalance, i.e. a comparison of the actual drum speed and its target speed. The first solution has the disadvantage of requiring additional sensors, which significantly increases the cost of the machine. The second solution implies that the control of the speed of the drum is not of very good quality, so that the difference between the target speed and the real speed remains large enough to be usable. This results in poorer accuracy in adjusting the speed. In addition, application FR-A-2 629 484 teaches that the value of this difference depends on both the unbalance and the total inertia of the laundry, and decreases when the latter increases. Application FR-A-2 629 484 therefore proposes a method for measuring the inertia independently of the unbalance in order to take it into account. However, this complicates the process.

Document EP-A-0 313 339 describes an unbalance control device for a washing machine where the control signal is a motor current signal.

The present invention aims to overcome the above drawbacks by proposing a method which does not require the implantation of additional components, which is simple, compatible with a good quality speed control, and does not require the measurement of the inertia of the linen.

To this end, it relates to a method of the type defined above, characterized in that the amplitude of the variation of said current flow angle over at least one revolution is determined as a magnitude representative of the unbalance of the drum.

In the process of the invention, the applicant has used the fact that, even if the speed control is of very good quality, the angle of current flow varies during a revolution in a way which is related at unbalance, since it is necessary to supply more current to the motor to raise the mass of unevenly distributed laundry than to lower it. The amplitude of the variation in the angle of passage over a revolution is therefore representative of the unbalance. The method of the invention does not require additional components, the microprocessor used for speed control, and which controls the value of the passage angle being easily programmable to determine the amplitude of the variations in the passage angle .

In the preferred implementation of the method of the invention, before carrying out a spin by centrifugation, said amplitude of the variation of the angle of change at speed is determined to be less than that of the spin, the amplitude is compared thus determined at a series of thresholds separated by ranges, and a spin speed value is selected as a function of the range in which said amplitude is found.

This process is particularly precise without requiring the determination of the total inertia of the laundry in the drum. Indeed, as will be seen below, the Applicant has been able to demonstrate, experimentally, a good correlation between the amplitude of the variations in the angle of passage at low speed and the amplitude of the movements of the tank under the 'effect of unbalance at high speed, displacements whose importance can be kept within tolerable limits by selecting a fairly low value of the spin speed.

The present invention also relates to a machine for spinning laundry by centrifugation, for implementing the above method, machine comprising an alternating current motor for driving said drum, a device for controlling the speed of said motor by adjusting the the angle of passage of the current passing through it, and means for controlling the speed of rotation of the drum as a function of the unbalance of the laundry in the drum, machine characterized in that it comprises means for determining the amplitude of the variation of said current flow angle, over at least one revolution of the drum, as a quantity representative of the unbalance.

• la figure 1 représente un schéma par blocs des circuits de commande du moteur d'une machine à laver et à essorer le linge selon l'invention,
  et,
• les figures 2a et 2b représentent des diagrammes temporels du courant traversant le moteur, dans deux configurations du balourd, respectivement.

The present invention will be better understood on reading the following description of the preferred implementation of the method of the invention, as well as of the preferred embodiment of the machine of the invention, made with reference to the accompanying drawings, on which ones :

• FIG. 1 represents a block diagram of the control circuits of the motor of a washing machine and of spinning the laundry according to the invention,
  and,
• Figures 2 a and 2 b show time diagrams of the current flowing through the motor, in two unbalance configurations, respectively.

A washing machine and wringing machine for which the speed is to be controlled as a function of the unbalance of the laundry in the drum comprises first of all, with reference to FIG. 1, an alternating current motor 2, mounted in series here with a triac 5, the assembly being connected to an alternating voltage source 6.

The motor output shaft 21 drives on the one hand the drum 1 by means of a reduction gear 22 and on the other hand a tachometric generator 3.

A microprocessor-based circuit 4 receives the voltage from the source 6 via an interface circuit 64, and the output voltage from the generator 3, via an interface circuit 34.

Circuit 4 controls, via an interface circuit 45, the triac 5 control electrode. Circuit 4 also receives a setpoint signal PR from the programmer of the machine, and which indicates to it no program we are.

The device which has just been described operates as follows. In normal operation, without unbalance, the tachometer generator 3, the circuit 4 and the triac 5 form a speed control loop which controls the triac so that the actual speed of the drum remains equal to a set value. The actual speed of the drum 1 is measured using the tachometric generator which, for example comprising eight pairs of poles, delivers a sinusoid whose frequency is equal to eight times the frequency of rotation of the motor. This sinusoid is transformed, in circuit 34, into a pulse train transmitted to circuit 4. The latter compares the value of the frequency of this pulse train with a set value, and adjusts, in a known manner, the value of the angle of passage of the current I in the motor 2 by triggering the conduction of the triac 5 at the appropriate time.

In the absence of unbalance, that is to say when the load of laundry is regularly distributed in the drum, and when the set speed is constant, the angle of current flow remains constant, regardless of the position of the drum.

However, in the presence of imbalance, this is not so. By way of example, we have considered, in FIGS. 2 a and 2 b , the case where, the speed of the drum 1 being high enough for the laundry 11 to be pressed against the wall of the drum 1, the laundry has poorly distributed, which is the cause of an imbalance.

In FIG. 2 a , the shape of the current I is shown during the portion of the tower of the drum 1 during which the laundry package 11 is to be mounted. It appears that the angle of passage of the current, noted T _M , takes a relatively large value, linked to the fact that the motor 2 must provide a force to mount the laundry.

In FIG. 2 b , the shape of the current I has been shown when the drum has turned half a turn relative to its position in FIG. 2 a , that is to say when the laundry package 11 descends. In this case, the force to be supplied by the motor is considerably reduced, which results in a significant reduction in the angle of passage of the current, which takes a value T _m less than the previous value T _M.

La grandeur A représente l'amplitude de la variation, sur un tour du tambour, de l'angle de passage du courant.The invention proposes taking, as a representative quantity of the unbalance, the amplitude A according to the formula:

${\text{A = T}}_{\text{M}}{\text{- T}}_{\text{m}}$

The quantity A represents the amplitude of the variation, over one revolution of the drum, of the angle of current flow.

It is especially useful to detect unbalance when you want to spin by centrifugation. To this end, before the actual spin, the circuit 4 controls the motor 2 so that the speed of the drum takes an intermediate value between the washing speed and the speeds causing an effective spin. For example, the washing or rinsing speeds being a few tens of revolutions per minute, and the spinning speeds of several hundred revolutions per minute, the intermediate value of the speed is 100 revolutions per minute. This speed is sufficient to cause a plating of the laundry by centrifugation, and therefore to detect any imbalance, while being low enough to cause no damage, even in the event of significant imbalance. During this intermediate speed step, circuit 4 therefore measures the amplitude A. During the next step, circuit 4 compares the measured value to a series of thresholds defining ranges of values, and selects a value of spin speed as a function of the range in which said value is found.

For example, for a particular type of washing machine, powered at 50 Hz, if the amplitude A, expressed here in microseconds and not in degrees, is greater than 300 microseconds, circuit 4 does not allow spinning, if amplitude A is between 270 and 300 microseconds, circuit 4 selects a spin speed equal to 300 revolutions per minute and if amplitude A is less than 270 microseconds, circuit 4 selects a spin speed equal to 900 rpm.

For this type of machine, these values have been established from the following table, which results from an experiment on a prototype. Distributed load (kg) Unbalance load (kg) A (micro-seconds) Displacement of the tank at 500 rpm (mm) Selected spin speed (rpm) 2 0.5 146 4 900 2 0.8 292 5 300 2 1 308 > 10 No spin 3 0.5 128 3 900 3 0.8 212 4 900 3 1 270 5 300 3 1.2 304 8 No spin 4 0.5 154 4 900 4 0.8 214 5 900 4 1 300 7 No spin

The previous table shows in particular the good agreement between the value of the amplitude A and that of the displacement of the tank, which was measured on the prototype to have a decision criterion. This agreement remains true even if the distributed load, that is to say the total inertia of the laundry, varies, which makes it possible in practice to disregard the value of this total inertia.

The present invention is obviously not limited to the washing machine which has just been partially described. It can also be applied to spinning or drying machines.

Claims (4)

1. A process for controlling the rotational speed of the drum (1) of a centrifugal spin drying machine according to the unbalanced mass of the laundry (11) in the drum (1), the said machine being provided with an alternating current motor (2) to drive the said drum (1), and an automatic control device (3, 4, 5) for controlling the speed of the laid motor (2) by adjusting the angle of passage of the current (I) though it, a process characterised in that the amplitude of the variation (T_m, T_M) of the said angle of passage of the current during at least one rotation of the drum is determined as a size representative of the unbalanced mass.
2. A process according to claim 1, in which, prior to carrying out a centrifugal spin drying operation, the said amplitude of the variation of the angle of passage at a lower speed than those of the spin drying is determined, the amplitude thus determined is compared with a series of thresholds separated by ranges, and a spin drying speed value is selected according to the range in which the said amplitude is located.
3. A centrifugal spin drying machine for laundry for carrying out the process according to one of claims 1 or 2, the machine comprising an alternating current motor (2) to drive the said drum (1), an automatic control device (3, 4, 5) for controlling the speed of the said motor (2) by adjusting the angle of passage of the current (I) though it, and means (4) for controlling the rotational speed of the drum (1) according to the unbalanced mass of the laundry (11) in the drum (1), the machine being characterised in that it comprises means (4) for determining the amplitude of the variation (T_m, T_M) of the said angle of passage of the current during at least one rotation of the drum (1) as a size representative of the unbalanced mass.
4. A machine according to claim 2, in which, prior to a centrifugal spin drying operation, the determination means (4) determine the said amplitude of the variation of the angle of passage at a lower speed than those of the spin drying, comparison means (4) are provided to compare the amplitude thus determined with a series of thresholds separated by ranges, and selection means (4) are provided to select a spin drying speed value according to the range in which the said amplitude is located.

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