Patent Publication Number: US-10323351-B2

Title: Method for operating a tumble dryer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to German Application No. 10 2015 217 667.3, filed Sep. 15, 2015, the contents of which are hereby incorporated herein in its entirety by reference. 
     TECHNOLOGICAL FIELD 
     The invention relates to a method for operating a tumble dryer in order to thereby dry damp laundry. In particular, the invention relates to controlling the drying process as a function of identifying, in as largely an automated manner as possible, the major fabric content or the major fibres of the laundry to be dried. 
     BACKGROUND 
     US 2008/104860 A1 discloses measuring the absolute atmospheric moisture in the tumble dryer. The loading quantity, in particular as weight, and the residual moisture in the laundry can be determined from this. Therefore, the expected duration of the drying process can be determined and indicated to an operator. 
     BRIEF SUMMARY 
     The invention is based on the object of providing a method of the kind mentioned in the introductory part with which problems and disadvantages of the prior art can be avoided and it is possible, in particular, to provide a practical method with which the major fibre content of the laundry to be dried can be identified during operation of a tumble dryer for the purpose of adapting the operation of the tumble dryer, in particular in respect of temperature profile or maximum temperature. Sensitive fibres can be protected in this way. 
     This problem is solved by a method. Advantageous and preferred refinements of the invention are the subject matter of the further claims and will be explained in greater detail in the text which follows. The wording of the claims is included in the content of the description by express reference. 
     It is provided, for operation of the tumble dryer, that, after the start of the drying process for the damp laundry, which can start either at the same time or else can begin only after a few minutes, the moisture of the air in the tumble dryer or the time profile of the moisture of the air in the tumble dryer is detected or measured. In this case, the absolute moisture or atmospheric moisture can be measured, wherein a correspondingly suitable moisture sensor for absolute moisture measurement can be used for this purpose, as is disclosed, for example, in the above-mentioned document US 2008/104860 A1. As an alternative, the relative moisture in the air in the tumble dryer can also be measured using a corresponding moisture sensor. Moisture sensors of this kind for relative moisture measurement are now available at low cost and operate in a sufficiently accurate manner. The temperature of the air in the tumble dryer can advantageously additionally be detected over the course of time, in order to be able to in turn draw conclusions about the values for the required moisture in this way. 
     Measurement is performed primarily in the ascent region of the profile of the moisture or during an initial phase of the drying process. This can be, for example, during the first at most 10 minutes to 15 minutes, but rather at most 5 minutes. The measurement or detection can also advantageously start only after 1 to 3 minutes, in order to preclude inaccuracies which prevail at the very start. 
     In a subsequent step, the profile of the measured moisture is compared with stored profiles for the moisture over time. As an alternative, a gradient of the profile of the measured moisture, that is to say the gradient values of the moisture, can be compared with stored gradient threshold values of the moisture. This applies irrespective of whether the absolute moisture or the relative moisture is measured. In this case, corresponding profiles and/or gradient threshold values are stored, specifically for fibres from the group comprising cotton, wool and synthetic fibres. A synthetic fibre of this kind is primarily PE or polyamide. These profiles or gradient threshold values can be stored in a memory of a control system of the tumble dryer. Corresponding profiles, that is to say, as it were, curves which can be stored as a graph or effectively a complete continuous time profile, can be stored for the stored time profiles, for example for the first 10 minutes to 15 minutes. Simple values without a time profile can be stored for the gradient threshold values, for example as maximum gradient threshold values. As an alternative, the gradient threshold values are stored with a specific time, that is to say the time at which they are each typically exceeded or undershot, depending on the major fibre content or fabric content in the laundry to be dried. These gradient threshold values can lie, for example, at a point in time between 1 minute to 3 minutes and 10 minutes to 15 minutes, advantageously between 3 minutes and 10 minutes. This is also still the start of the drying process. 
     The greatest similarity can be identified during a comparison of the detected profile of the moisture in the tumble dryer with the three stored profiles, so that the major fabric content of the laundry to be dried is then associated with that fibre type of which the profile best corresponds to the detected time profile of the moisture. Deviations can be detected here directly or else, as it were, in an integrated manner, for example by means of the size of surface areas of a difference between the two profiles. In this case, both absolute values, for example maximum points or the connection points of the profile, and also relative values, such as percentage drop within a specific time, can be taken into consideration. 
     If, as an alternative, gradient values are compared at specific points in time, in particular during ascent, this is generally simpler and possibly even more accurate. If a stored upper gradient threshold value is exceeded, a major fabric content comprising synthetic fibres is identified for the laundry to be dried. If a stored low gradient threshold value is undershot, a major fabric content comprising wool or wool fibres is identified. If the detected gradient threshold value lies between the upper gradient threshold value and the lower gradient threshold value, a major fabric content comprising cotton or cotton fibres is identified. As stated, this can be done at a suitable point in time. In this alternative, it can be easily identified that evaluation or identification is easier. It is only necessary for the gradient value to be ascertained from the detected time profile of the moisture at a specific point in time, for example after 3 minutes to 10 minutes, this being straightforward. This detected gradient value is then compared with the stored gradient threshold values and the laundry to be dried is classified under one of the three categories. 
     The operation of the tumble dryer or the drying process can then be adapted on the basis of this. This applies, for example, for the temperature profile or a maximum temperature which is very important, in particular, for the synthetic fibres. Synthetic fibres must not be dried with too high a heat since otherwise they become brittle relatively quickly. The same also applies for wool, wherein here it is also the case that the rotation speed or the drum movement of the tumble dryer should be rather slow or gentle since wool is relatively sensitive. This is generally less important for cotton since cotton can be dried relatively easily at high temperatures and with pronounced drum movement. 
     The gradient threshold values can be stored not only as individual values at precisely one point in time, but rather also as a graph or as a time profile. In this case, it is also possible to attempt to detect the gradient values and to compare the gradient values with the stored gradient threshold values several times, that is to say at several points in time, and at prespecified times. 
     In addition to detecting the moisture in the tumble dryer, in particular the absolute moisture, the temperature in the tumble dryer can also be detected in terms of its time profile. Detection of the absolute moisture allows the temperature in the tumble dryer to be detected over the course of time, at least when at the start of the drying process, and then to determine the relative moisture from this. In this case, a temperature sensor and a moisture sensor can be formed separately from one another, in order to be able to use accurate and at the same time cost-effective sensors in each case. 
     As an alternative, the relative moisture in the tumble dryer can likewise be measured directly using a corresponding moisture sensor which is designed for relative moisture measurement. In this case, it is additionally also possible to detect the temperature of the air in the tumble dryer over the course of time by means of a temperature sensor, in order to obtain further information. In particular, the absolute moisture can then be calculated from this. In this case too, it should be possible to detect the temperature of the air in the tumble dryer, in addition to the moisture, at least at the start of the drying process. 
     If, on account of the comparison of the detected time profiles or the detected gradient values, the major fibre material of the laundry to be dried is identified, operation of the tumble dryer can likewise be matched to the major fibre material. This applies, in particular, for temperature profile, maximum temperature, drum movement, rotation speed and/or duration of the drying process. Therefore, on the one hand, damage to the fibres or to the laundry to be dried can be avoided. Secondly, the drying process can be carried out within the possible thresholds in a rapid and/or energy-efficient manner. 
     These and further features can be gathered from the claims as well as from the description and the drawings, wherein the individual features can each be implemented in their own right or in groups in the form of sub-combinations in the case of an embodiment of the invention and in other fields, and may represent advantageous and inherently patentable embodiments for which protection is claimed here. The subdivision of the application into individual sections and sub-headings does not restrict the general validity of the statements made therein. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Exemplary embodiments of the invention are schematically illustrated in the drawings and will be explained in greater detail in the text which follows. In the drawings: 
         FIG. 1  shows an internal view of a tumble dryer; and 
         FIG. 2  shows a graph for various profiles of the moisture over time in the case of loading with laundry comprising different fibres for the tumble dryer according to  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a tumble dryer  11  for the method according to the invention. The illustration is limited to the functionally important parts and is intended merely to show how these important parts function. Laundry  14  containing residual moisture after washing and/or spin-drying is located in a loading compartment  12 . This loading compartment  12  is usually turned or rotated, but this does not play an important role for the invention. Air is introduced into the loading compartment  12  via an air inlet  16 . The air flow is generated by the fan  17 , wherein air is heated by the downstream heater  18  in order to dry the laundry  14 . Similarly, an air outlet  20  is routed out of the loading compartment  12  to the outside, this identifying the tumble dryer  11  as an exhaust-air tumble dryer. As is known of tumble dryers of this kind, the hot air is therefore supplied to the laundry  14 , absorbs moisture and transports the moisture via the air outlet  20  to the outside, in order to dry the laundry in this way. 
     In order to detect the moisture in the exhaust air, a moisture sensor  22  is arranged in the air outlet  20 . A moisture sensor  22  of this kind is known to a person skilled in the art and does not need to be explained in any detail here. The moisture sensor  22  is connected to a control system  24 , just like the fan  17  and the heater  18 . The control system  24  has a memory  25 , possibly even integrated in it, in which various values or profiles can be stored, this being discussed in further detail below. 
     In addition to the moisture sensor  22 , a temperature sensor  23  which is likewise connected to the control system  24  is arranged in the air outlet  20 . The temperature sensor is advantageously a customary temperature sensor, particularly advantageously with resistance measurement. The moisture sensor  22  can advantageously be designed to measure the absolute moisture, that is to say the moisture of the exhaust air in the air outlet  20 . As an alternative, the moisture sensor can also be a moisture sensor for relative moisture measurement, which may be more cost-effective. In order to then obtain the absolute moisture of the air in the air outlet  20 , the temperature sensor  23  is provided in the air outlet  20 . In this case, the temperature sensor is arranged just in front of the moisture sensor  22 , but can also be arranged opposite or just behind the moisture sensor. A tumble dryer of this kind is substantially known from US 2008/104860 A1 which is cited in the introductory part and to which reference is explicitly made in this respect. 
     Apart from for an exhaust-air tumble dryer  11  illustrated in  FIG. 1 , the invention can also be used in modified form for a condensation tumble dryer. To this end, a corresponding moisture sensor is provided in an air outlet from the loading compartment in front of a downstream condensation device. Therefore, the moisture in the exhaust air can also be detected there. 
     It is not necessary to explain the general manner of operation of a tumble dryer here. According to the invention, after the laundry  14  is introduced into the tumble dryer  11 , that is the loading compartment  12  of the tumble dryer, the drying process is started with operation of the fan  17  and of the heater  18  in order to heat the air. In this case, the absolute moisture is detected in the air outlet  20  by means of the moisture sensor  22  over the course of time in this exemplary embodiment. The curves for the absolute moisture are firstly known from the above-mentioned document US 2008/104860 A1 and illustrated once again in  FIG. 2 . The figure illustrates four different profiles, specifically a solid thin profile CO 1  for a quantity of 1.2 kg of exclusively cotton fibre laundry with a residual moisture content of 40%. The solid thick profile CO 2  shows a quantity of 4.5 kg of cotton fibre laundry with a moisture content of 50%. The dashed thin profile PE shows a quantity of 1.2 kg of polyester fibre laundry and a moisture content of 40%. The thin dash-dotted profile WO shows a quantity of 1.2 kg of wool laundry with a moisture content of 40%. The ascent region cited in the introductory part or the beginning of the drying process is considered to be the first minutes here, specifically at most measured for the first 15 minutes, advantageously for the first 3 minutes to 10 minutes. In this case, it can be seen in this ascent region that the profile is indeed similar but has a different gradient depending on the type of fibres of the laundry, as a result of which different profiles are of course also produced. The profile PE for the synthetic fibre, that is to say polyester, has the highest gradient at the start. As expected, WO for wool has the lowest gradient. The two profiles CO 1  and CO 2  for cotton are situated in-between, wherein, as expected, the profile for the greater quantity of damper cotton as profile CO 2  is steeper and rises more sharply than for the lower quantity of cotton as profile C 01 . 
     The gradient values of the profiles after 3 minutes are marked by way of example. At this point in time, the profile PE has the greatest gradient with the gradient value S PE , and the profile WO has the lowest gradient with the gradient value S WO . The gradient values are illustrated by the corresponding straight lines here. The two gradient values for the profiles CO 1  and CO 2  with the gradient value S CO1  and with the gradient value S CO2  are situated between the first gradient values. If these gradient values, which have been detected by the moisture sensor  22 , at the 3-minute point in time are then compared with gradient threshold values, which are stored in the memory  25 , a slight distinction can be drawn as follows. A stored upper gradient threshold value S GO , which is illustrated using a dotted line, is situated between the gradient values of the profiles PE and CO 2 . A stored lower gradient threshold value S GU , which is also illustrated using a dotted line, can be situated between the gradient values of the profiles CO 1  and WO. Depending on whether the upper gradient threshold value S GO  is exceeded or undershot and the lower gradient threshold value S GU  is exceeded or undershot at this point in time of t=3 minutes, the laundry can be divided into the fibre groups PE, CO or WO, that is to say synthetic fibres, cotton or wool. Whether the present gradient value is actually exactly detected is of secondary importance, provided that the measurement is accurate enough to be able to safely and reliably and accurately establish that one of the gradient threshold values has been exceeded or undershot. Even if the differences in the gradient values in  FIG. 2  do not appear to be particularly significant, they are significant from a computational point of view. For example, the gradient value S PE  is approximately 25% greater than the gradient threshold value S GO , even though it does not appear to be. 
     Measurement relatively early after the start of the drying process or in the initial phase of the drying process, that is to say after the 3 minutes for example, not only has the advantage that identification of the exclusive or major fabric content is then possible at a very early stage, in order to select a maximum temperature to be relatively low and possibly also to select a rotation speed to be low for example in the case of sensitive fibres, such as synthetic fibres or wool, so that damage can be avoided. Furthermore, the ascents are further particularly different here, so that even particularly good identification or distinguishing of the respective gradient values is possible. At point in time t=10 minutes, it would no longer be possible to draw a distinction as well or actually even at all. 
     As an alternative to the above-described detection of gradient values at an early point in time, it is also possible for specific profiles to be stored in the memory  25  of the control system  24 . These specific profiles are distinguished in a characteristic manner, for example the very slow drop in moisture after reaching the maximum value in the case of wool since moisture can be drawn from wool only with difficulty. In contrast, the synthetic fibre is very pronounced in respect of the maximum value and the speed of the drop since, as is known, moisture can be drawn from synthetic fibres much more quickly. The profiles for cotton are situated approximately between those for wool and synthetic fibres. Therefore, these basic profiles or types of profile could also be stored and a conclusion about the major fabric content in the laundry  14  could be drawn by comparing a profile, which is detected over time, of the atmospheric moisture in the air outlet  20  with a stored profile. However, to this end, it would be necessary to wait at least for the maximum value to be reached and for a subsequent drop. However, this firstly means a certain waiting time until identification. Secondly, the relatively sensitive synthetic fibres or wool may possibly already be damaged in the case of drying of the laundry  14  at a very high temperature. In this respect, comparing the gradient values is considered to be the most advantageous option because it is also very quick.