EP2035617B1 - Method for detecting the standstill of a drum in a tumble drier, and tumble drier which is suitable for this purpose - Google Patents

Description

The invention relates to a method for detecting the stoppage of a drum in a drum dryer and a drum dryer suitable for this purpose (hereinafter also referred to as "tumble dryer").

In a conventional clothes dryer, wet laundry located in a generally rotating drum is dried by passing a heated air stream through the drum and thus through the laundry, which is capable of removing moisture from the laundry, thereby gradually drying the laundry becomes.

The supplied air stream (process air stream) is heated in a supply line in front of the drum ("laundry drum") by means of a heater and after passing through the laundry in the drum either discharged to the outside (exhaust air dryer) or fed to a heat exchanger in which cooled the air flow and the moisture precipitates as condensate. In both cases, similar problems arise with regard to the safe operation of the tumble dryer. The warm process air removes the laundry depending on the degree of humidity and temperature of the laundry a corresponding amount of moisture. It is important that after reaching a certain degree of drying of the laundry excessive heating of the process air flow and thus both overheating of the laundry and overheating of the clothes dryer is avoided.

A particularly critical condition, which can lead to damage of laundry and affect the reliability, is a stoppage of the laundry drum, which occurs for example when tearing a drive belt of the drum.

A cracked drive belt can be detected mechanically via a limit switch. However, this requires an additional component complexity with a corresponding control. Another possibility for detecting such a standstill or a broken drive belt is that the rotational movement of the drum is detected in particular by optoelectronic components. However, this solution also requires an additional component complexity with appropriate electronic control.

That's how it describes WO 2005/064065 A1 a device for monitoring a drive belt of a clothes dryer with a rotatable drum for receiving laundry, a motor, a drive belt between the drive motor and drum, a tensioning device which is movable for tensioning the drive belt relative to the drive belt in a clamping movement direction, and a switch which operates becomes when the tensioning device is moved in the clamping movement direction over a predetermined distance to turn off the clothes dryer.

Thus, although mechanical and optical methods for detecting a drum state are known, but associated with additional costs.

In the EP 0 889 155 B1 is a method for detecting improper operating conditions in a hot air dryer with laundry drum described. In this method, the temperature in the process air stream above a heater and before the laundry drum is detected periodically with a first temperature sensor, from values recorded at successive times a difference value or a gradient is formed, which has a predetermined value, hereinafter referred to as "first permissible difference value is compared, wherein when the newly formed difference value is absolutely greater than the first allowable difference value, a count value is increased by one step and this count value is compared with a predetermined count value. If the current count is greater than the predetermined count, the heater of the clothes dryer is turned off and / or a warning operating status display is activated. If, on the other hand, the determined difference value is smaller than the permissible difference value, the current difference value is compared with a predetermined second allowable difference value, which corresponds to a permissible temperature increase resulting from a lint filter blockage. At the in EP 0 889 155 B1 described method, the temperature between the heater and the laundry drum is detected.

Another method for detecting a critical state or an impermissible operating state, in particular for detecting a fault occurring due to reduced process air flow in a drum dryer during the drying of wet laundry by means of process air is off DE 43 37 735 A1 known. The process air stream is heated by a heater in a supply air duct in front of a drum of the drum dryer and enters after passage through the drum in an exhaust duct. In such a method, a measured value of the residual moisture content of the Laundry as criterion for the detection of the critical condition. In addition, the temperature of the process air is measured with a temperature sensor arranged in the exhaust duct behind the drum. The temperature measured in this way is evaluated as a further criterion with respect to the determination of the critical state.

In the EP 0 906 985 B1 is a method for detecting an impermissible operating state in an electronically controlled tumble dryer, in particular the state of motion of the laundry drum, described in which the electrical conductance of the laundry is determined by means of electrodes which touch the laundry at least temporarily. Changes in the guide values are observed in order to make a decision on the continuation of the operation from a change. If, in this case, the change in the conductance over a period of several periods corresponding to the values compared corresponds to a preset small fluctuation range, a standstill of the laundry drum is detected and a corresponding signal is displayed, and the drying process can be aborted.

The presence of a standstill is determined relatively late in these methods, since on the one hand the first temperature sensor between the heater and the drum is still flowed around with the normal amount of process air, so that the change in the temperature of the process air at the first temperature sensor relatively late effect, and on the other a change in the conductivity of the laundry below a predetermined level can be detected only with a certain delay.

An object of the present invention is therefore to provide an improved method for detecting the stoppage of a drum in a drum dryer.

This object is solved by the subject matter of claim 1. Preferred embodiments are given in the dependent claims 2 to 6.

Furthermore, the present invention has for its object to provide a corresponding drum dryer, in which a standstill of the drum can be detected in good time and reacted to it.

This object is achieved by a drum dryer with the features of claim 7. A preferred embodiment of the drum dryer is in Claim 8 specified. Moreover, further preferred embodiments of the drum dryer from preferred embodiments of the method according to the invention.

In the inventive method for detecting the standstill of a drum in a drum dryer during drying wet laundry by means of process air, which is heated by a heater in a supply air duct in front of the drum and after passing through the drum in an exhaust duct, the temperature of the process air by means measured in the exhaust duct downstream of the drum second temperature sensor and evaluated the change in the temperature of the process air with respect to the determination of the stoppage of the drum. In this case, to determine the standstill of the drum and a measurement of the conductance of existing in the drum dryer laundry used. For this purpose, the conductivity of the laundry is measured in the drum and evaluated the change in the conductance in terms of determining the stoppage of the drum.

In this case, the temperature of the process air at the second temperature sensor is preferably detected periodically, a difference value or a gradient, which is compared with a predefined first permissible difference value, formed from values acquired at successive times, wherein if the newly formed difference value is absolutely greater than predetermined difference value, a set to zero at the beginning of drying count is increased by one step. This count is compared in this preferred embodiment with a predetermined count and, if the current count is greater than the predetermined count, the heater (heater) of the drum dryer is turned off and / or a warning operating status display is activated.

In a preferred embodiment of the above embodiment, the difference value is compared with a predetermined second allowable difference value, which corresponds to a permissible temperature increase resulting from a lint screen clogging (lint filter temperature difference value) with a determined difference value which is smaller than the first permissible difference value. , Most preferably, if the determined difference value is less than the lint screen temperature difference value, increasing a lint count value set to zero at the beginning of drying by one step, comparing the newly formed lint count with a predetermined allowable lint count and if the newly formed lint count is greater is the allowable lint count value, an indication or indication of lint clogging is enabled.

According to the invention, the overheating of the process air flow can be determined as such due to a stopped drum or such overheating hazard can be detected in good time before reaching the high temperature, whereupon appropriate countermeasures, in particular the shutdown of the heater can be done. As a result, damage to components and located in the drum dryer laundry can be avoided.

With the method according to the invention not only an overheating of the process air due to the drum standstill, but also the clogging of a lint filter can be detected be because an inadmissibly added lint filter also leads to an increase in the temperature of the process air stream due to the reduced flow rate.

At the same heat output rapidly higher temperatures are reached in both cases, which can be detected with the inventively provided second temperature sensor and lead in time for switching off the heater. Simultaneously with or prior to the shutdown of the heater, an indicator with an indication of a clogged lint filter may also be activated. Thereafter, an operator of the drum dryer is able to perform a corresponding lint screen cleaning, and due to appropriately preselected values, a display for prompting the lint filter may be displayed long before its complete clogging and thus the drum dryer can always operate in a satisfactory and energy efficient operating condition ,

The process according to the invention can advantageously be used both in a condensation dryer and in an exhaust air dryer.

Particularly advantageously, the temperature of the process air stream is detected in the exhaust duct downstream of the drum from the beginning of drying, whereby the entire temperature profile is detected in the drum dryer.

In a preferred embodiment of this method, the conductivity is detected periodically during drying and the current detected conductance is compared with at least one previously detected conductance. If the change in the conductance determined from the values compared over a period of several periods corresponds to a previously set small fluctuation range, an indication of the standstill of the drum and / or a shutdown of the heating takes place in this embodiment.

The measurement of the conductance of the laundry (also referred to as laundry control value or laundry voltage signal) in the drum of a drum dryer can be realized, for example, by the drum having a measuring electrode and at the same time serving as the second electrode. To measure the conductivity of the laundry, the drum is then usually connected to a ground potential of the drum dryer and is the measuring electrode via a series resistor to a constant voltage connected. When the drum is stationary, the laundry control signal remains constant. The missing fluctuation of this signal can be used to detect the standstill.

In an advantageous embodiment of the method according to the invention, the small fluctuation range of the Wäscheleitwertes is preset in dependence on the loading amount of the drum. This has the advantage that an inadmissible shutdown of the drying process when rotating the drum is avoided. At very high loading and especially at the beginning of the drying process at high humidity of the laundry may result that constantly wet laundry is applied to the electrodes and the change in conductance is therefore very low. The fluctuation range of the conductance value is then preset accordingly low. The fluctuation range may also be zero or substantially zero.

As a rule, the measured values for temperature and, if appropriate, the laundry control value are evaluated in an electronic control device in order to obtain a more reliable statement about the standstill of the drum. Since the temperature at the drum outlet to avoid damage to the laundry is generally limited by the control device to defined values (limit temperature), the heating power is reduced. In connection with the reconnection of the heater when falling below a threshold temperature, therefore, an oscillation (clocks) of the heating power is generated, which can be used for the determination of a drum standstill.

Preferably, a neural network, a fuzzy logic, a sharp mathematical combination or a combination of these means and methods come into question for the evaluation algorithm in the control device.

Advantageously, when the stoppage of the drum is indicated, the drying process is stopped, so that a partial overheating of the laundry, which can occur when the drum is at a standstill, is avoided, even if the drying process is unobserved by a user.

The present invention also relates to a drum dryer suitable for carrying out the method described above with a drum for drying wet laundry by means of process air, a heating device in a supply air duct in front of the drum for Heating the process air and an exhaust duct downstream of the drum, wherein in the drum, a measuring electrode for measuring the conductance of the laundry is provided and is located in the exhaust duct, a second temperature sensor.

In a further preferred embodiment, the drum dryer has a control device for evaluating the temperature measured by the second temperature sensor and, if appropriate, the conductivity value of the laundry measured by the measuring electrode with regard to the determination of a drum standstill.

The inventive method for detecting the drum standstill and the drum dryer according to the invention have numerous advantages. The safety during operation of the drum dryer is increased. With the method according to the invention, it is possible, due to the temperature rise caused by the drum standstill, to detect the state of the drum dryer far in advance of the actual reaching of too high a temperature and to switch off the heating in good time before reaching too high a temperature. Thus, not only the components of the drum dryer itself, but also the laundry parts located in the drum are safely protected against overheating.

In addition, the solution according to the invention is cost-neutral, since possibly existing sensors for the temperature and possibly the Wäscheleitwert can be used. In addition, the method according to the invention is characterized by a higher accuracy compared to previous software-supported methods.

Further details of the invention will become apparent from the following description of exemplary embodiments of the method and a drum dryer suitable for this method. It is referred to Fig. 1 and Fig. 2 ,

In Fig. 1 a partial section through a drum dryer is shown, showing both the variant of an exhaust air dryer type (solid lines) and the type of a condensation air dryer with circulating air principle (dashed lines).

Fig. 2 shows a schematic circuit structure for carrying out an embodiment of the method.

In FIG. 1 is shown in partial sectional view of a drum dryer 1. This has in its upper part on a program control device 3, which is adjustable by an operating handle 5 and may preferably include a fuzzy processor controller, not shown here.

The drum dryer 1 has a drum 2, which is accessible via a pot 9 from a feed door 11 and placed on the wet laundry in the drum 2 and can be removed again after drying.

At the lower back of the drum dryer 1, a process air opening 13 is arranged, which sucks in air from outside via a fan 15 and flows into a process air channel 17. From the process air duct 17, the fresh process air flows via a heating device 18 to the inlet 21 of the drum 2. Between the heating unit 18 and the drum 2, a first temperature sensor 10 is provided which measures the temperature of the effluent from the heater process air and thus in particular a criterion for the correct function of the heater 18 supplies. The process air traverses the drum 2 and flows at the outlet 23 through an exhaust duct 25. Behind the drum 2, a second temperature sensor 12 is arranged in the exhaust duct 25, which periodically detects the temperature of the process air at predetermined time intervals and the measured value of a corresponding control device (not shown). supplies.

In the exhaust duct 25 is a lint filter 26. The process air flows through the exhaust duct 25 to an exhaust outlet 27, from where it flows back into the open air. The drum dryer 1 of this embodiment thus operates on the exhaust air principle.

However, the process air circuit can also be closed to form a forced air tumble dryer, wherein the process air is guided from the exhaust duct 25 to a condenser 29. The condenser 29 is designed as a heat exchanger in which the moist process air is cooled and condenses the increased humidity and separates from the process air. The process air is then forwarded by the fan 15 in the process air duct 17 again. The condensate may be in FIG. 1 not shown manner at a suitable location removed from the drum dryer 1 or pumped into a condensate tank, from which it can be removed by hand.

To form a working in the recirculation condensation dryer, the manifold 28 of the exhaust duct 25 and the fan 15 are reversed and connected to the respective nozzle 31 and 32 of the condenser 29.

Fig. 2 shows the drum 2 of a drum dryer 1, which contains a measuring electrode 6. As a counter electrode, the drum 2 acts as such. To determine the conductance of the laundry, the drum 2 is connected to the mass 4 of the drum dryer 1 and the measuring electrode 6 is connected via a series resistor 8 to a constant voltage source 7. The laundry in the drum 2 has a laundry resistance 19, which is connected on the one hand via the drum 2 with the mass 4 of the drum dryer 1 and on the other hand via the measuring electrode 6 sporadically with the series resistor 8 and thus forms a voltage divider with this. At the connection point between the laundry resistor 19 and the series resistor 8, a measurement signal 20 is obtained, which serves as a measure of the conductance of the laundry (Wäscheleitwert). The measuring signal 20 can be advantageously supplied to the input of an anti-aliasing filter 16 whose output is connected to an analog input of a control device 14. The second temperature sensor 12 is located in the exhaust duct 25 behind the output of the process air flow from the drum 2, see. Fig. 1 , The second temperature sensor 12 is also connected to the control device 14 for evaluating the signals measured by it.

Upon movement of the laundry in the drum 2 by the rotation of the laundry gets at least partially in contact with the measuring electrode 6 and thus causes a time-varying signal for the conductance (conductivity measurement signal 20). Each time the measuring electrode 6 is touched by a piece of laundry or whenever the laundry resistance 19 measured between the measuring electrode 6 and the drum 2 changes, the conductivity measuring signal 20 changes markedly. If no item of laundry touches the measuring electrode 6 or a piece of laundry only slightly touches the electrode and therefore a lower conductance is measured, the conductivity measuring signal 20 has a minimum value. In contrast, with very good electrical connection between the measuring electrode 6 and the laundry, the conductivity measuring signal 20 will have a maximum value.

If the drum 2, due to a broken drive, for example, by a broken drive belt, resting, the conductance does not change or only slightly, either one and the same garment always rests against the measuring electrode 6 or, if they are in is located at the top of the drum 2, no laundry is permanently applied and thus the conductance is zero.

When the drum 2 comes to a standstill as described, the contact between the laundry items in the drum 2 and the process air passing through them changes. The process air absorbs less moisture from the laundry and therefore cools much less than with moving drum 2. This leads immediately after a standstill to a significant increase in temperature at the second temperature sensor 12, which is used as an indication of the standstill. At the first temperature sensor 10 (see. Fig. 1 ) occurs such a temperature increase at best to a very small extent, and only after a certain delay.

In the control device 14, the changes in the temperature at the second temperature sensor 12 as well as the changes in the conductance measured by means of the measuring electrode 6 are correspondingly evaluated, as also described above. In this case, the temperature of the process air by means of the second temperature sensor 12 is measured to detect the standstill of the drum 2, and evaluated the change in the temperature of the process air with respect to the determination of the standstill of the drum 1. For this purpose, the temperature of the process air at the second temperature sensor 12 is detected periodically, formed from respectively successive times values respectively a difference value or a gradient, which is compared with a predetermined first allowable difference value, wherein if the newly formed difference value is absolutely greater than the predetermined difference value is to increase a count set to zero at the beginning of the drying by one step. This count value is compared with a predetermined count value and, if the current count value is greater than the predetermined count value, the heater 18 is turned off and a warning operating status indicator on the operating handle 5 is activated.

Additionally, with a determined difference value that is smaller than the first allowable difference value, the current difference value is compared with a predetermined second allowable difference value corresponding to a permissible temperature increase resulting from clogging of the lint filter 26 (lint temperature difference value). If the determined difference value is less than the lint filter temperature difference value, increasing a lint count value set to zero at the beginning of drying by one step increases the newly formed lint count value with a predetermined allowable lint count value and if the newly formed lint count is greater than the allowed lint count, then an indication or indication of lint clogging is enabled.

In addition, a measurement of the conductance of the laundry present in the tumble dryer 1 is used to determine the standstill of the drum 2. For this purpose, the conductance of the laundry in the drum 2 is measured and evaluated the change in the conductance in terms of determining the stoppage of the drum 2. For this purpose, the conductivity is detected periodically during drying and the current detected conductance is compared with at least one previously detected conductance. If the change in the conductance determined from the values compared over a period of several periods corresponds to a previously set small fluctuation range, the standstill of the drum 2 is displayed and the heater 18 is switched off.

The measurement of the conductance of the laundry (also referred to as laundry control value or laundry voltage signal) in the drum 2 is realized by the measuring electrode 6 and the drum 2 itself as a second electrode. To measure the conductance of the laundry, the drum 2 is connected to a ground potential of the drum dryer 1 and the measuring electrode 6 is connected via the series resistor 8 to a constant voltage. When the drum 2 is stationary, the laundry control signal remains constant. The missing fluctuation of this signal is used to detect the standstill.

Suitably, the small fluctuation range of the Wäscheleitwertes depending on the loading amount of the drum 2 is preset. This has the advantage that an inadmissible shutdown of the drying process during rotation of the drum 2 is avoided. At very high loading and especially at the beginning of the drying process at high humidity of the laundry may result that constantly wet laundry is applied to the electrodes 2 and 6 and the change in conductance is therefore very low. The fluctuation range of the conductance value is then preset accordingly low. The fluctuation range may also be zero or substantially zero.

The measured values for temperature and Wäscheleitwert be evaluated in the electronic control device 14 in order to obtain a safer statement about the stoppage of the drum 2. Since the temperature at the outlet of the drum 2 for preventing damage to the laundry is generally limited by the control device 14 to defined values (limit temperature), the power of the heater 18 is reduced. in the In connection with the reconnection of the heater 18 falls below a threshold temperature, therefore, an oscillation (clocks) of the heating power is generated, which can be used for the determination of a standstill of the drum 2.

Preferably, for the evaluation algorithm in the control device 14, a neural network, a fuzzy logic, a sharp mathematical combination or a combination of these means and methods in question.

Claims (8)

1. Method for detecting a critical state in a tumble dryer (1) which could lead to damaged laundry and be detrimental to the operational safety during the drying of damp laundry by means of process air which is heated by a heating device (18) in an air feed duct (17) before a drum (2) in the tumble dryer (1) and which after passing through the drum (2) enters an air extraction duct (25), wherein the temperature of the process air is measured by means of a second temperature sensor (12) arranged in the air extraction duct (25) behind the drum (2), and the temperature is evaluated in relation to a determination of the critical state, characterised in that the change in the temperature of the process air is evaluated in relation to a determination of a stationary state of the drum (2), which is the critical state to be detected.
2. Method according to claim 1, characterised in that the conductivity (20) of the laundry in the drum (2) is measured and the change in conductivity is also evaluated in relation to establishing the stationary state of the drum.
3. Method according to claim 1 or 2, characterised in that the temperature of the process air at the second temperature sensor (12) is sensed periodically, a difference value or a gradient, as appropriate, is formed from values sensed in each case at successive time points, this being compared with a preset first permissible difference value, wherein, if the newly formed difference value is absolutely greater than the first permissible difference value, a count value, which at the start of the drying is set to zero, is increased by one increment, this count value is compared with a preset count value and, if the current count value is greater than the preset count value, the heating device (18) is switched off and/or an operating state indicator (5) is activated.
4. Method according to claim 3, characterised in that in the case that a temperature difference value determined is less than the first permissible difference value, the difference value determined is compared with a preset second permissible difference value (lint filter temperature difference value) which corresponds to a permissible temperature rise resulting from the blockage of a lint filter (26) in the tumble dryer (1).
5. Method according to claim 4, characterised in that if the difference value determined is less than the second permissible difference value, a lint filter count value which at the start of the drying is set to zero is incremented by one count value, the newly formed lint filter count value is compared with a preset lint filter count value and, if the newly formed lint filter count value is greater than the preset lint filter count value, an indication or statement that there is a blockage is activated.
6. Method according to one of the preceding claims, characterised in that the conductivity (20) is sensed periodically during the drying operation, the current sensed conductivity (20) is compared with at least one previously sensed conductivity value (20) and, if the change in the conductivity (20) determined from the values compared corresponds over an interval of several periods to a low range of fluctuation set previously, then an indication is given of the stationary state of the drum (2) and/or the heating device (18) is switched off.
7. Tumble dryer (1) for performing the method according to one of claims 1 to 6 with a drum (2) for drying damp laundry by means of process air, a heating device (18) in an air feed duct (17) before the drum (2), for heating up the process air, an air extraction duct (25) behind the drum (2), and a second temperature sensor (12) arranged in the air extraction duct (25) behind the drum (2), characterised in that it has a control device (14) for evaluating the temperature measured by the second temperature sensor (12) in respect of a determination of a stationary state of the drum and the control device (14) is designed for the evaluation of the change in the temperature, measured by the second temperature sensor (12), in respect of a determination of a stationary state of the drum.
8. Tumble dryer (1) according to claim 7, characterised in that it includes a measuring electrode (6) for measuring the conductivity (20) of the laundry, and the control device (14) is also designed for the evaluation of the change in the conductivity (20) of the laundry, measured by the measuring electrode (6), in respect of a determination of a stationary state of the drum.

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