EP0926292B1 - Method for determining the drying progression in a drying phase and machine using such method - Google Patents

Description

The present invention relates to a method for determining of the evolution of drying in a drying process, as well as a machine for implementing this process.

Currently in the field of dryers and machines washer-dryers, we actually determine the end of the drying process, either by measuring the evolution of the drying air temperature and / or its derivative using a thermistor placed in the drying air circuit (this temperature increases, at a substantially constant air flow, during at the end of the drying cycle), either by measurement, using electrodes at the contact of the linen, the resistivity of the linen (this increases as and drying measurement).

The result of the thermistor measurement process depends on parameters that cannot be controlled or not controlled. The measurement result, at constant laundry load (type and quantity of laundry), depends on the tension power supply (in general, its nominal value can be understood between 187 v and 254 v, and may vary over time) and the accuracy of components in particular due to manufacturing tolerances, these components being those that can influence the drying process (the rated power of the air heater can vary by ± 10%, the temperature of the limiting elements can vary by ± 5 ° C, and the tolerance on the thermistor value can influence ± 3 ° C on the dynamics of drying). The measurement result, at constant environment (voltage, heating power and drying air temperature) depends on the load to dry (mass and type of laundry). In addition, the drying phases laundry (temperature rise and temperature stabilization phase, drying stage phase, during which the temperature is practically stable, and end of drying phase) are difficult differentiable, which does not allow to foresee sufficiently in advance the end of drying, and even less to effectively regulate the power of drying air heating.

In the case of the resistivity measurement, the result depends on randomly, load to dry. It's easier to dry, so reliable, a high load than a low load, because in the latter case the result depends on the average position of the load in relation to measuring electrodes. This results in large variations in the measurement in depending on the mass and type of textiles to be dried.

In addition to their poor reproducibility, these known methods require numerous statistical tests, resulting in significant delays in development, and therefore a high cost of this development.

It should also be noted that the results of the measurements made according to these known processes become even more random when occur in drying out of outdoor events such as power outage electric, opening the machine door for adding laundry in progress drying, changing the setpoint (in general: drying time) by the user or if the machine structures are changed.

We also know in document FR 1 290 592 a dryer in which a regulating device, controlling the drying air flow and the heating of this drying air, is implemented from a measurement of the relative humidity of the air coming out of the laundry.

The subject of the present invention is a method for determining the evolution of drying during a drying process for various products, for which the quality of the determination does not depend or practically does not depend non-controllable or uncontrolled parameters, in particular: the voltage of the electrical sector, the dispersion of component or parameter values can influence the drying process (nominal power of the element heating, temperature thresholds when operating close to limits admissible by the components, temperature as measured by the thermistor or dispersion of the electrode measurement results), mass and type of laundry to be dried, cut off from the power supply, door opening by user, ambient temperature and humidity ...

The present invention also relates to a machine (dryer or washer-dryer) using this process, the cost price of which is not significantly increased by this implementation, and which is simple to use and maintain.

• mesure, au début du processus de séchage, d'une humidité relative maximale de l'air de séchage, à l'arrêt de la ventilation d'air de séchage ;
• mise en oeuvre, lorsque cette humidité relative descend en-dessous d'un seuil qui est fonction de ladite humidité relative maximale, d'une dernière phase du processus de séchage, au cours de laquelle on fait alternativement circuler, dans le circuit d'air de séchage de la machine, de l'air de séchage avec au moins deux débits différents ;
• mesure des valeurs d'humidité relative pour les deux débits différents ;
• comparaison d'une relation établie à partir desdites mesures de valeurs d'humidité relative avec une relation prédéterminée dépendante d'une quantité de produit à sécher ; et
• déduction de l'état de séchage des produits en fonction du résultat de ladite comparaison.

The method of the invention is characterized in that it comprises the following steps:

• measurement, at the start of the drying process, of a maximum relative humidity of the drying air, when the drying air ventilation stops;
• implementation, when this relative humidity drops below a threshold which is a function of said maximum relative humidity, of a last phase of the drying process, during which one alternately circulates, in the air circuit machine drying, drying air with at least two different flow rates;
• measurement of relative humidity values for the two different flow rates;
• comparison of a relationship established from said measurements of relative humidity values with a predetermined relationship dependent on an amount of product to be dried; and
• deduction of the state of drying of the products according to the result of said comparison.

Advantageously, the relative humidity measurements are made using components called "humidistors".

• la figure 1 est un diagramme montrant l'évolution d'une relation de différence de valeurs d'humidité relative pour différentes charges de linge, conformément à l'invention, et
• la figure 2 est un bloc-diagramme d'un exemple de circuit de détermination du degré de séchage, conforme à l'invention.

The invention will be better understood on reading the detailed description of an embodiment, taken by way of nonlimiting example and illustrated by the appended drawing, in which:

• FIG. 1 is a diagram showing the evolution of a relation of difference in relative humidity values for different loads of laundry, in accordance with the invention, and
• FIG. 2 is a block diagram of an example of a circuit for determining the degree of drying, in accordance with the invention.

The invention is described below with reference to a washer-dryer or to a dryer, hereinafter referred to as a machine, but it is fine understood that it can be used in various drying processes at using an air flow, this air can be more or less hot.

In the machine implementing the method of the invention, the rates drying air humidity are measured using a component called "Humidistance". This component is in the form of a capacitor whose dielectric constant is modified according to the humidity of the air ambient. The capacity of this capacitor varies according to the relative humidity ambient air present between its electrodes. More generally, we can use instead of the humidistance any electrical component whose response electric varies according to the humidity of the ambient air, like for example resistive components whose resistance varies as a function of this humidity. he it is understood that if a component other than a humidity is used, changes his connection circuit to the processing circuit (microcontroller described below) controlling the drying machine. To determine this humidity relative, we insert the capacitor in the tuning circuit of an oscillator, and the frequency of this oscillator is measured. This frequency is therefore a function the capacitance of the capacitor, which is itself a function of humidity relative air in which this capacitor is immersed. So it's easy to determine the relative humidity at all times by measuring a value of frequency.

In the case of a machine such as a dryer, the humidity relative drying air can vary between 0 and 100%. The precision of relative humidity measurement is generally only necessary at the end of drying, when the relative humidity decrease gradient begins to increase slightly, after remaining substantially constant during the central part of the drying process, and we want to avoid laundry overdrying and saving air heating energy from drying. In addition, the relative humidity measuring device must be even withstand condensation without damage or drift from its characteristics. The humidity, used as described below, meets these requirements.

There is at least one such humidity in the air circuit machine, and we connect it to an oscillator followed by a circuit suitable for controlling the drying circuit and offering the user the possibility of choosing a determined degree of drying. The realization of such an oscillator and such an operating circuit is obvious for the skilled person on reading this description, and will not not described in detail.

The invention is particularly intended for machines in which the drying air flow can either be interrupted periodically or take at least two different values. There are, for example, machines in which the ventilation turbine is asymmetrical and rotates alternately in each of the two directions. In one direction of rotation, the ventilation rate is high (approximately 150 m ³ / h), and in the other direction of rotation, the flow is lower (approximately 40 m ³ / h). At the beginning of the drying process, when the air flow is high, the vaporization of the water contained in the laundry is important. On the other hand, when the air flow is low or zero, the water vaporization is lower.

As the drying process proceeds, the difference in relative humidity for the two air flows attenuates and tends towards a null value. Indeed, at the start of drying a damp cloth, the water molecules also permeate the "skin" (peripheral part) of linen fibers as their heart, and those of the "skin" are easily vaporized. Then the water molecules permeating the heart migrate to the periphery, but this migration movement is relatively slow (its speed depends in particular on the nature of the fibers and the arrangement of the linen in the machine drum). It was found that at the end of drying, this migration speed is low and substantially constant, whatever the drying air flow. The process of the invention takes advantage of this phenomenon by monitoring at least at the end of drying said difference in humidity for determine the end of the drying process.

The diagram in FIG. 1 represents the evolution of the relative humidity rate H _R for two different masses of wet linen as a function of time. The curves of FIG. 1 are recorded on a prototype or pre-series machine, then their remarkable values are memorized in memories such as ROMs installed on series machines, to be exploited in the manner described below. These masses are for example 1 and 4 kg. The drying process comprises three phases denoted respectively P0, P1 and P2.

For all these phases of the laundry drying process, the relative humidity measurements H _R are carried out at the stabilized stop of the drying air flow. Also, for all these phases, the air flow varies periodically. Each period T comprises a succession of four elementary times: [Dmax, A, Dmin, A], the meanings of which are as follows: Dmax, Dmin: maximum and minimum flow rate respectively, A: stopping the drying air ventilation. The values of Dmax and Dmin are different depending on the phases of the drying process. Thus, according to an example, for the phases P0 and P1, the values of Dmax and Dmin are respectively 140 m ³ / h and 40 m ³ / h and their respective durations within a period T are 31 seconds and 6 seconds, the downtime A being 2 seconds. For this same example, during phase P2, the values of the flow rates are the same, but their durations are 12 seconds for Dmax and 25 seconds for Dmin, the downtime A always being 2 seconds. Of course, the values cited for this example may all be different in other examples without departing from the scope of the invention.

The phases P0, P1 and P2 are determined as follows. Phase P0 begins with the start of the drying process and ends when the mass of laundry and the parts of the machine heated by the flow of hot drying air have reached the maximum temperature that this hot air can give them. This end of P0 coincides with the instant when the relative humidity H _R of the drying air reaches its maximum (H _RO ), H _R being measured when the ventilation stops (for example after 25 seconds of stop , to be able to obtain a stabilized value of the relative humidity) between two successive periods T, T being as defined above. To simplify the implementation, it is possible, in series machines, to take P0 of fixed duration equal to the greatest value measured in the laboratory on pre-series machines. The measurement frequency of H _R can be variable depending on the machine and the mass of laundry. It usually takes just a few measurements to determine the end of P0, which occurs fairly quickly after the start of drying (usually after a few minutes). It can be seen that the values of H _RO are clearly different for the two loads of linen taken as an example (these values of H _RO are denoted H _RO - 1 and H _RO -4.

Then begins phase P1, during which relative humidity values called H _R are measured. These values are measured between two periods T, also when the ventilation is stopped, for example after 25 seconds of stop. It can be seen that H _R is constant, then decreases appreciably linearly over time, and more rapidly for low loads of laundry.

This is due in particular to the fact that the drying air passes more difficult in a large amount of laundry (occupying almost completely the entire interior volume of the machine drum) than in a small amount of laundry, and therefore takes less moisture.

The end of phase P1 is determined as follows. We can for example take as a reference the instant when the drying rate of the laundry reaches 20% (the drying rate being defined as the ratio between the mass of water remaining in the laundry and the mass of laundry). Since this drying rate cannot be measured directly in a machine in service with the user, the corresponding relative humidity H _R1 is determined in the laboratory, in an identical machine. This rate is noted x. H _RO , with o <x <1, for different quantities of wet laundry, H _R1 being always measured as described above. For the sake of clarity, only two curves have been shown in FIG. 1, corresponding to wet laundry masses of 1 and 4 kg, but in reality, we proceed with different other masses.

Phase P2 begins as soon as the relative humidity drops below x. H _RO corresponding. During this entire phase, which theoretically ends with the complete drying of the laundry, two different measurements are made for each load of laundry: a measurement of H _R1 as during phase P1, and a measurement of H _R2 during elementary times when the drying air flow is equal to Dmin. The measurements of H _R1 and H _R2 during phase P2 are carried out more often than the measurements of H _R1 during phase P1, because their values decrease very rapidly. We note for different values of the difference (H _R1 - H _R2 ) the corresponding drying rate (or an equivalent indication such as laundry ready to be ironed, laundry completely dry, ...), because, as we see according to Figure 1, this difference decreases with time, and therefore with the drying rate of the laundry, and is canceled when the laundry is completely dry. It will be noted in this FIG. 1 that the curves relating to different loads of laundry have phases P1 and P2 of different durations and that the ends of the phases P2 are sufficiently distant from each other over time so that a processor can easily distinguish them.

Consequently, it suffices to memorize in the memory of each serial machine the shapes of the different curves H _R1 and H _R2 (or characteristic points of these curves, between which an interpolation can take place) for different loads of laundry, these different curves having been recorded on a prototype or pre-series machine, in order to very easily determine the end of drying of the laundry. For this purpose, it is not necessary for the user to know the mass of linen, since the curves relating to different masses and / or qualities of linen are sufficiently differentiated from one another. It is therefore sufficient for the machine control device to carry out a few humidity rate measurements (by means of frequency measurements) at “characteristic” instants, that is to say at the start of drying, to determine H _RO (when the humidity is at its maximum), then a little before the foreseeable end of P1 (that is to say a short time before going down to x. H _RO ), and then periodically during of P2, by regularly alternating the measurements of H _R1 and H _R2 until the difference (H _R1 - H _R2 ) reaches the desired value, which is a function of the drying rate (or a similar indication) displayed by the user. It will be noted that the curves relating to a small load of laundry (a few pieces of laundry) and to a maximum load of laundry (approximately 4 to 5 kg, for a standard machine) are sufficiently distant from each other so that the control circuit of the machine can, even before the end of PO, quickly determine what is the curve relating to any load of laundry to be dried, even if this load differs significantly in composition from that used to establish the curves.

It is important to note that these measures are practically independent of the drying air temperature (especially during P2) and the various aforementioned phenomena involved in the process of drying (mains voltage, reloading of laundry, drifting components ...).

The humidity of an air flow being a diffuse phenomenon, and not concentrated in a small area of the section of this flow, the positioning of the humidity does not need to be performed in a specific location. He is by therefore easy to place it in a place where it least risks fouling with fluff from the dried laundry.

The method of the invention can be implemented both in drying air exhaust machines than in condensation.

Advantageously, the accuracy of determination of the drying rate by determining the average type of product to be drying and its drying characteristics (textile in this case) by example by measuring the slope of the curves in Figure 1. Indeed, nature textile fibers influence the speed of migration of water molecules from their hearts to the surface, so the drying speed. In the extreme case of fibers absorbing practically no water, the evaporation of the retained water superficially is fast, and therefore the drying is fast, which increases the slope of the corresponding curve. It then suffices to modulate the speed of drying of these products.

Another possibility to refine this precision is to associate with the humidity a temperature probe, which allows to take into account the influence of temperature variations on humidity variations relative, and therefore correct these. In addition, it is thus possible to determine the absolute humidity of the drying air.

The circuit 1 shown schematically in Figure 2 comprises, in as a sensor signal processing device and a device for calculation, a digital microcontroller 2. A main capacitive sensor 3, of the type "humidity", is connected to an oscillator 4 followed by a circuit 5 of setting in shape delivering variable frequency rectangular signals in depending on the capacity of the sensor 3. The output of circuit 5 is connected to a digital input 6 of the microcontroller 2. The microcontroller 2 is also connected to a memory 8 in which values of drying rate as a function of different relative humidity values and / or relative humidity difference values for the air flow rates of the machine. If you don't have a humidity, you can use a resistive humidity sensor (7). This alternative solution has been represented in broken lines in Figure 3. This sensor 7 is connected to an analog input 6 'of the microcontroller 2. This input 6' is connected, inside the microcontroller to an analog / digital converter (not shown). A temperature sensor 9, for example a thermistor, is connected to a other analog input 10 of the microcontroller 2. The microcontroller 2 is obviously programmed for the skilled person on reading the present description. The temperature sensor 9 makes it possible to correct, if if applicable, the information provided by the sensor 3. An air flow sensor 11 is connected to another input 12 of the microcontroller. This input 12 is an analog or digital input, depending on the type of sensor 11. In the simplest case, this sensor 11 is a tachometer integral with the drying air circuit turbine.

Claims (9)

1. Method for determining progress with drying during a drying process comprising several drying phases (P0, P1, P2), implemented in a machine in which a flow of heated air is made to circulate, characterised in that it comprises the following steps:

   measuring, at the start of the drying process, a maximum relative humidity (H_RO) of the drying air, at the stoppage of the drying air ventilation;

   implementing, when this relative humidity descends below a threshold (x.H_RO) which is a function of the said maximum relative humidity (H_RO), a last phase (P2) of the drying process during which drying air is made to circulate in alternation in the drying air circuit of the machine, at at least two different flow rates (D1, D2);

   measuring the relative humidity values (H_R1, H_R2) for the two different flow rates (D1, D2);

   comparing a relationship established from the said measurements of relative humidity values (H_R1, H_R2) with a predetermined relationship dependent on a quantity of product to be dried; and

   deducing the state of drying of the product according to the result of the said comparison.
2. Method according to Claim 1, characterised in that the said predetermined relationship is a difference between relative humidity values measured for the two different flow rates.
3. Method according to Claim 1 or 2, characterised in that the temperature of the drying air is also measured at at least one point in its circuit in order to correct the relative humidity measurements where necessary.
4. Method according to one of the preceding claims, characterised in that the slope of the law for the change in relative humidity is measured in order to take account of the type of product to be dried and its drying characteristics.
5. Machine for drying products by means of a drying air flow, comprising a microcontroller (2) to which there is connected at least one relative humidity sensor (3, 7), characterised in that it comprises a drying air flow sensor (11) connected to the microcontroller (2) and a memory (8) in which there are stored drying level values according to values of differences in relative humidity for the air flow rates of the machine (D1, D2).
6. Machine according to Claim 5, characterised in that at least one of the relative humidity sensors (3) is a capacitive sensor of the "Humidistance" type.
7. Machine according to one of Claims 5 or 6, characterised in that at least one of the relative humidity sensors (7) is a resistive sensor.
8. Machine according to Claims 5 to 7, characterised in that it also comprises at least one drying air temperature sensor (9) .
9. Machine according to one of Claims 5 to 8, characterised in that it is a tumble dryer or a washer-dryer.

Images