LAUNDRY DRYER WITH OPTICAL SENSORS

Abstract

 The invention relates to a dryer (1) and a method for drying wet laundry (9), wherein the dryer (1) comprises a drum (3), a drum motor (4), an air inlet (51), an air outlet (52) and an air flow generator (6), wherein the dryer (1) further comprises a control unit (8) for controlling the rotational velocity and the flow rate. The dryer (1) is provided with a first optical sensor (73) and a second optical sensor (74) for detecting presence of the laundry (9) in the first quarter (33) and the second quarter (34), respectively, of the upper half (32) of the drum (3) volume. The control unit (8) is arranged for controlling the rotational direction (R1) and the rotational velocity according to a desired pattern in function of the optical sensors (73).

Description

BACKGROUND

[0001] The invention relates to a dryer, in particular a tumble dryer, for drying wet laundry.

[0002] WO 2010/151128 A2 discloses a tumble dryer for drying laundry using substantially unheated, ambient air. The tumble dryer has two air inlet and two air outlets for generating alternating, mutually crossing air flows. A first sensor and a second sensor are provided for giving signal to a control system, which signals correspond with the air humidity of the air sucked in through a first and a second of the two air inlets, respectively. Furthermore, a third sensor is provided for giving a third signal to the control system, which signal corresponds with the air humidity of the air discharged from the drum. As soon as the value measured by the third sensor is substantially lower than or equal to a reference value, the laundry is dry and the control system switches off the drive of the tumble dryer. The reference value is a criterion on the basis of which the tumble dryer switches off, for instance as soon as the air humidity of the air coming from the drum is substantially equal to the air humidity of the air outside or inside the house.

[0003] When the abovementioned tumble dryer sucks in ambient, unheated air from and discharges process air into the same room, the moist extracted from the laundry will considerably contribute to the humidity of the ambient air inside said room. The drying process will thus become increasingly inefficient. Furthermore, the criterion for determining the dryness of the laundry may be influenced by the ambient humidity, thereby giving a false indication of the dryness of the laundry and prematurely terminating the drying process.

[0004] It is an object of the present invention to provide a dryer, in particular a tumble dryer, and a method for drying wet laundry, wherein the effectiveness and/or the efficiency of the drying can be improved.

SUMMARY OF THE INVENTION

[0005] According to a first aspect, the invention provides a dryer, in particular a tumble dryer, for drying wet laundry, comprising a drum for receiving the wet laundry, a drum motor for rotating the drum at an adjustable rotational velocity in a first rotational direction, an air inlet and an air outlet arranged in flow communication with the drum, and an air flow generator for generating an airflow with an adjustable flow rate into the drum though the air inlet and out of the drum through the air outlet, wherein the dryer further comprises a control unit that is operationally connected to the drum motor and the air flow generator for controlling the adjustable rotational velocity and the adjustable flow rate, respectively, wherein the volume of the drum is divided into an upper half and a lower half, wherein the upper half is divided into a first quarter and a second quarter downstream of the first quarter in the first rotational direction, wherein the dryer is provided with a first optical sensor and a second optical sensor for detecting presence of the laundry in the first quarter and the second quarter, respectively, of the upper half of the drum volume, wherein the control unit is arranged for rotating the drum in the first rotational direction while increasing the rotational velocity from a preset lower velocity limit until the presence of the laundry is detected only in the first quarter by the first optical sensor, wherein the control unit is arranged for subsequently keeping the rotational velocity substantially constant until the presence of the laundry is detected in both the first quarter and the second quarter of the drum volume by the first optical sensor and the second optical sensor, respectively, after which the control unit is arranged for reducing the rotational velocity in the first rotational direction until the presence of the laundry is detected only in the first quarter again by the first optical sensor.

[0006] The optical sensors can ensure that the laundry tumbles or falls down through the center of the drum, where optimal interaction with the air flowing through the drum can be obtained for an optimal drying of the laundry.

[0007] In an embodiment the drum motor is arranged for rotating the drum in a second rotational direction opposite to the first rotational direction, wherein the control unit is arranged for rotating the drum alternatingly in the first rotational direction and the second rotational direction, wherein, when rotating the drum in the second rotational direction, the control unit is arranged for increasing the rotational velocity in the second rotational direction from the preset lower velocity limit until the presence of the laundry is detected only in the second quarter by the second optical sensor, wherein the control unit is arranged for subsequently keeping the rotational velocity substantially constant until the presence of the laundry is detected in both the first quarter and the second quarter of the drum volume by the first optical sensor and the second optical sensor, respectively, after which the control unit is arranged for reducing the rotational velocity in the second rotational direction until the presence of the laundry is detected only in the second quarter again by the second optical sensor. By rotating the laundry in two directions, the effectiveness of the drying can be further improved.

[0008] In an embodiment the first optical sensor and the second optical sensor are arranged for detecting the presence of the laundry within the radially outer 10% of the diameter of the drum volume. The radially outer placement of the optical sensors can improve the accuracy of the control based on the optical sensors, as the laundry is only detected when it passes in the radially outer regions of the drum volume.

[0009] In an embodiment the first optical sensor is arranged, referring to the hours of a clock, for detecting the presence of the laundry between the 10 o'clock and 11 o'clock position with respect to the drum volume, wherein the second optical sensor is arranged, again referring to the hours of a clock, for detecting the presence of the laundry between the 1 o'clock and 2 o'clock position with respect to the drum volume. The optical sensors can be placed sufficiently far apart to allow the laundry to fall through the center of the drum, while only being detected by one of the optical sensors.

[0010] In an embodiment the dryer further comprises a first humidity sensor, at or near the air inlet, that is operationally connected to the control unit for sending a first signal with a value indicative of a first humidity of the air flowing into the drum to the control unit and a second humidity sensor, at or near the air outlet, that is operationally connected to the control unit for sending a second signal with a value indicative of a second humidity of the air flowing out of the drum to the control unit, wherein the control unit is arranged for ending the drying when the value of the second signal is equal and remains equal to the value of the first signal despite the increases in the rotational velocity. When the value of the second signal no longer increases, this can be an indication that the laundry has dried to or has approached the dryness of the humidity of the air in the room in which the dryer is placed. As the dryer uses the air in the room to dry, the laundry cannot be dried further. The laundry can now be considered sufficiently dry. However it is clear that alternative embodiments are possible for ending the drying. The drying could for example be ended when the second signal reaches a value indicative for a predetermined humidity at which the laundry is sufficiently dried, for example a humidity of 60% or lower, preferably 55% or lower. When the humidity in the air flowing out of the drum during drying the laundry is reduced to at or below this predetermined humidity for dried laundry, the laundry can be considered sufficiently dried and the drying can be ended. This is particularly advantageous, when for example the first signal indicative of the first humidity of the air flowing into the drum is low when compared to the second signal and remains low. This means when the humidity of the air in the room is low, for example 30% and does not rise substantially. In such a case setting a predetermined humidity for dried laundry of for example 55%, ensures that drying will be ended as soon as the laundry is considered sufficiently dry, this means for example 55%, and will not continue drying until the laundry reaches the lower humidity of the room, this means for example 30%. In this way the drying time and energy consumption is reduced. It is clear that in general the drying could be ended when the value of the second signal reaches a value indicative of a predetermined humidity for dried laundry, which is in the range of 100% to 250% of the value of the first signal.

[0011] According to a second aspect, the invention provides a dryer, in particular a tumble dryer, for drying wet laundry, comprising a drum for receiving the wet laundry, a drum motor for rotating the drum at an adjustable rotational velocity, an air inlet and an air outlet arranged in flow communication with the drum, and an air flow generator for generating an airflow with an adjustable flow rate into the drum though the air inlet and out of the drum through the air outlet, wherein the dryer further comprises a control unit that is operationally connected to the drum motor and the air flow generator for controlling the adjustable rotational velocity and the adjustable flow rate, respectively, wherein the dryer further comprises a first humidity sensor, at or near the air inlet, that is operationally connected to the control unit for sending a first signal with a value indicative of a first humidity of the air flowing into the drum to the control unit and a second humidity sensor, at or near the air outlet, that is operationally connected to the control unit for sending a second signal with a value indicative of a second humidity of the air flowing out of the drum to the control unit, wherein the control unit is arranged for controlling the drum motor and the air flow generator by switching between different modes based on the first signal and the second signal, wherein the modes comprise:

a) a drying mode in which the control unit is arranged to increase the rotational velocity and/or the flow rate when the value of the first signal is below a preset upper humidity limit and the value of the second signal is decreasing;

b) a dehumidification mode in which the control unit is arranged to decrease the rotational velocity and/or the flow rate when the value of the first signal is above the preset upper humidity limit.

[0012] By increasing the rotational velocity and/or the flow rate when the second signal is decreasing, the extraction of moisture or water from the laundry can be maximized while keeping the value second signal relatively constant. If the humidity of the air being drawn into the drum increases to above the preset upper humidity limit, for example as a result of the relatively humid air that is discharged from the drum mixing with the air being drawn in, the dehumidification mode can effectively decrease the humidity of the air being discharged. This allows for the dryer according to the invention to draw air from and discharge air into the same, naturally ventilated room. By using the humidity of the air available in the naturally ventilated room, instead of heating the air, the dryer according to the invention can operate very efficiently.

[0013] In an embodiment the drying mode is an incremental drying mode comprising two phases;
a stable phase in which control unit is arranged to keep the rotational velocity and/or the air flow substantially constant when the value of the second signal is substantially constant or increasing;
an incremental phase in which the control unit is arranged to incrementally increase the rotational velocity and/or the air the flow rate when the value of the second signal is decreasing.

[0014] By incrementally increasing the rotational velocity and/or the air flow, the moisture or water can be maximally extracted after each increment, before increasing the rotational velocity and/or the flow rate again.

[0015] In an embodiment the control unit is arranged for starting or restarting the drying mode when the value of the first signal is below a preset lower humidity limit, preferably of 50 percent relative humidity or less. The drying mode can thus be started (or restarted when dehumidification mode has been completed) when the humidity of the air outside the dryer has favorable conditions for drying.

[0016] In an embodiment the control unit is arranged for increasing the rotational velocity in the drying mode from a preset lower velocity limit towards a preset upper velocity limit, wherein the control unit is arranged for reducing the rotational velocity to the preset lower velocity limit once the preset upper velocity limit has been reached. The laundry can thus be dried in cycles, wherein for each cycles, the rotational velocity is increased between the lower velocity limit and the upper velocity limit.

[0017] In an embodiment the control unit is arranged for decreasing the rotational velocity and/or the flow rate in the dehumidification mode to fifty percent or less of the highest rotational velocity and/or the flow rate, respectively, in the drying mode prior to switching to the dehumidification mode. The reduced rotational velocity and/or flow rate reduces the amount of moisture or water exiting the dryer with the air being discharged from the air outlet.

[0018] In an embodiment the control unit is arranged to stop the rotation of the drum in the dehumidification mode. By stopping the rotation of the drum all together, the humidity of the air flowing out of the drum can be decreased significantly, thereby allowing the air being drawn into the drum to decrease.

[0019] In an embodiment the control unit is arranged to keep the flow rate substantially constant during the drying mode. The humidity of the air flowing out of the drum can thus be controlled by controlling solely the rotational velocity of the drum.

[0020] In an embodiment the control unit is arranged for ending the drying mode when the value of the second signal no longer increases as a result of the increase in the rotational velocity, or when the value of the second signal is equal and remains equal to the value of the first signal despite the increase in the rotational velocity during the drying mode. When the value of the second signal no longer increases, this can be an indication that the laundry has dried to or has approached the dryness of the humidity of the air in the room in which the dryer is placed. As the dryer uses the air in the room to dry, the laundry cannot be dried further. The laundry can now be considered sufficiently dry.

[0021] In an embodiment the dryer further comprises a temperature sensor at or near the air inlet, operationally connected to the control unit for sending a third signal with a value indicative of a temperature of the air flowing into the drum to the control unit, wherein the control unit is arranged for setting the preset upper humidity limit based on the value of the third signal. When the temperature of the air flowing into the drum is relatively high, e.g. above 25 degrees Celsius, the preset upper humidity limit may be set higher than in a situation when the temperature of the air flowing into the drum is relatively low, e.g. below 18 degrees Celsius. The high temperature of the air in combination with the relatively high relative humidity may still provide acceptable drying performance, while in lower temperatures, the drying performance is to a large extent dependent on a relatively low relative humidity.

[0022] In an embodiment the preset upper humidity limit is in the range of 60 to 70 percent relative humidity. These percentages can still be considered comfortable or habitable conditions in the room where the dryer is placed.

[0023] In an embodiment the air flow generator has a flow rate capacity in the range of 600 to 1600 times the volume of the drum per hour, and preferably has a flow rate capacity of at least 600 cubic meters per hour, most preferably 800 cubic meters per hour. The high flow rate increases the amount of water or moisture that can be effectively extracted from the laundry.

[0024] In an embodiment the air flow generator is placed upstream of the drum, preferably at or near the air inlet. Preferably, the air flow generator is a ventilator or a blower. The air flow generator is thus arranged for blowing air into the drum, instead of drawing air through the drum.

[0025] In an embodiment the dryer is arranged for drawing air into the drum via the air inlet from a naturally ventilated room and/or for drawing ambient, unheated and/or variably humid air into the drum via the air inlet. The readily available air in the room can be used to dry the laundry.

[0026] In an embodiment the dryer is arranged for discharging air out of the drum through the air outlet into a room in which the dryer is placed, wherein the dryer is further arranged for drawing air into the drum via the air inlet from the same room. The dryer can thus recycles the air in the room.

[0027] In an embodiment the dryer operates without a heating element for actively heating the air flowing into the drum via the air inlet, or wherein the dryer comprises a heating element that is operationally connected to the control unit and the control unit is arranged for deactivating the heating element during when the value of the first signal is below the preset upper humidity limit. The air does not have to be heated by an electricity consuming heater.

[0028] In an embodiment the volume of the drum is divided into an upper half and a lower half, wherein the upper half is divided into a first quarter and a second quarter downstream of the first quarter in the first rotational direction, wherein the dryer is provided with a first optical sensor and a second optical sensor for detecting presence of the laundry in the first quarter and the second quarter, respectively, of the upper half of the drum volume, wherein the control unit is arranged for increasing the rotational velocity in the drying mode from a preset lower velocity limit until the presence of the laundry is detected only in the first quarter by the first optical sensor, wherein the control unit is arranged for subsequently keeping the rotational velocity substantially constant until the presence of the laundry is detected in both the first quarter and the second quarter of the drum volume by the first optical sensor and the second optical sensor, respectively, after which the control unit is arranged for reducing the rotational velocity in the first rotational direction until the presence of the laundry is detected only in the first quarter again by the first optical sensor. The optical sensors can ensure that the laundry tumbles or falls down through the center of the drum, where optimal interaction with the air flowing through the drum can be obtained for an optimal drying of the laundry.

[0029] In an embodiment the drum motor is arranged for rotating the drum in a second rotational direction opposite to the first rotational direction, wherein the control unit is arranged for rotating the drum alternatingly in the first rotational direction and the second rotational direction in the drying mode, wherein, when rotating the drum in the second rotational direction, the control unit is arranged for increasing the rotational velocity in the second rotational direction from the preset lower velocity limit until the presence of the laundry is detected only in the second quarter by the second optical sensor, wherein the control unit is arranged for subsequently keeping the rotational velocity substantially constant until the presence of the laundry is detected in both the first quarter and the second quarter of the drum volume by the first optical sensor and the second optical sensor, respectively, after which the control unit is arranged for reducing the rotational velocity in the second rotational direction until the presence of the laundry is detected only in the second quarter again by the second optical sensor. By rotating the laundry in two directions, the effectiveness of the drying can be further improved.

[0030] In an embodiment the first optical sensor and the second optical sensor are arranged for detecting the presence of the laundry within the radially outer 10% of the diameter of the drum volume. The radially outer placement of the optical sensors can improve the accuracy of the control based on the optical sensors, as the laundry is only detected when it passes in the radially outer regions of the drum volume.

[0031] In an embodiment the first optical sensor is arranged, referring to the hours of a clock, for detecting the presence of the laundry between the 10 o'clock and 11 o'clock position with respect to the drum volume, wherein the second optical sensor is arranged, again referring to the hours of a clock, for detecting the presence of the laundry between the 1 o'clock and 2 o'clock position with respect to the drum volume. The optical sensors can be placed sufficiently far apart to allow the laundry to fall through the center of the drum, while only being detected by one of the optical sensors.

[0032] According to a third aspect, the invention provides a method for drying wet laundry with the aforementioned dryer, wherein the method comprises the step of controlling the drum motor and the air flow generator with the control unit by switching between different modes based on the first signal and the second signal, wherein the modes comprise:

a) a drying mode in which the rotational velocity and/or the flow rate are increased when the value of the first signal is below a preset upper humidity limit and the value of the second signal is decreasing;

b) a dehumidification mode in which the rotational velocity and/or the flow rate are decreased when the value of the first signal is above the preset upper humidity limit.

[0033] In an embodiment the drying mode is an incremental drying mode comprising two phases;
a stable phase in which the rotational velocity and/or the flow rate is kept substantially constant when the value of the second signal is substantially constant or increasing;
an incremental phase in which the rotational velocity and/or the flow rate are incrementally increased when the value of the second signal is decreasing.

[0034] In an embodiment the drying mode is started or restarted when the value of the first signal is below a preset lower humidity limit, preferably of 50 percent relative humidity or less.

[0035] In an embodiment the rotational velocity is increased in the drying mode from a preset lower velocity limit towards a preset upper velocity limit, wherein the rotational velocity is reduced to the preset lower velocity limit once the preset upper velocity limit has been reached.

[0036] In an embodiment the rotational velocity and/or the flow rate is decreased in the dehumidification mode to fifty percent or less of the highest rotational velocity and/or the flow rate, respectively, in the drying mode prior to switching to the dehumidification mode.

[0037] In an embodiment the rotation of the drum is stopped in the dehumidification mode.

[0038] In an embodiment the control unit keeps the flow rate substantially constant during the drying mode.

[0039] In an embodiment the drying mode is ended when the value of the second signal no longer increases as a result of the increase in the rotational velocity.

[0040] In an embodiment the drying mode is ended when the value of the second signal is equal and remains equal to the value of the first signal despite the increase in the rotational velocity during the drying mode.

[0041] In an embodiment the dryer further comprises a temperature sensor at or near the air inlet, operationally connected to the control unit for sending a third signal with a value indicative of a temperature of the air flowing into the drum to the control unit, wherein the method comprises the step of setting the preset upper humidity limit based on the value of the third signal.

[0042] In an embodiment the preset upper humidity limit is in the range of 60 to 70 percent relative humidity.

[0043] In an embodiment the flow rate is in the range of 600 to 1600 times the volume of the drum per hour, and preferably is at least 600 cubic meters per hour, most preferably at least 800 cubic meters per hour.

[0044] In an embodiment ambient, unheated and/or variably humid air is drawn into the drum via the air inlet.

[0045] In an embodiment the dryer discharges air out of the drum through the air outlet into a room in which the dryer is placed, wherein the dryer draws air into the drum via the air inlet from the same room.

[0046] In an embodiment the air flowing into the drum via the air inlet is not actively heated.

[0047] In an embodiment the dryer draws air into the air inlet from a naturally ventilated room.

[0048] In an embodiment the volume of the drum is divided into an upper half and a lower half, wherein the upper half is divided into a first quarter and a second quarter downstream of the first quarter in the first rotational direction, wherein the dryer is provided with a first optical sensor and a second optical sensor for detecting presence of the laundry in the first quarter and the second quarter, respectively, of the upper half of the drum volume, wherein the method comprises the steps of rotating the drum in the first rotational direction while increasing the rotational velocity in the drying mode from a preset lower velocity limit until the presence of the laundry is detected only in the first quarter by the first optical sensor, wherein the rotational velocity is kept substantially constant until the presence of the laundry is detected in both the first quarter and the second quarter of the drum volume by the first optical sensor and the second optical sensor, respectively, after which the rotational velocity in the first rotational direction is reduced until the presence of the laundry is detected only in the first quarter again by the first optical sensor.

[0049] In an embodiment the drum motor is arranged for rotating the drum in a second rotational direction opposite to the first rotational direction, wherein the method comprises the step of rotating the drum alternatingly in the first rotational direction and a second rotational direction, wherein, when rotating the drum in the second rotational direction, the rotational velocity is increased from the preset lower velocity limit until the presence of the laundry is detected only in the second quarter by the second optical sensor, wherein the rotational velocity is kept substantially constant until the presence of the laundry is detected in both the first quarter and the second quarter of the drum volume by the first optical sensor and the second optical sensor, respectively, after which the rotational velocity in the second rotational direction is reduced until the presence of the laundry is detected only in the second quarter again by the second optical sensor.

[0050] The aforementioned method and its dependent aspects have the same advantages as the corresponding aspects of the dryer according to the second aspect of the invention and will not be repeated hereafter.

[0051] According to a fourth aspect, the invention provides a method for drying wet laundry with the dryer according to the first aspect of the invention, wherein the method comprises the steps of rotating the drum in the first rotational direction while increasing the rotational velocity from a preset lower velocity limit until the presence of the laundry is detected only in the first quarter by the first optical sensor, wherein the rotational velocity is kept substantially constant until the presence of the laundry is detected in both the first quarter and the second quarter of the drum volume by the first optical sensor and the second optical sensor, respectively, after which the rotational velocity in the first rotational direction is reduced until the presence of the laundry is detected only in the first quarter again by the first optical sensor.

[0052] In an embodiment the method comprises the step of rotating the drum alternatingly in the first rotational direction and a second rotational direction, wherein, when rotating the drum in the second rotational direction, the rotational velocity is increased from the preset lower velocity limit until the presence of the laundry is detected only in the second quarter by the second optical sensor, wherein the rotational velocity is kept substantially constant until the presence of the laundry is detected in both the first quarter and the second quarter of the drum volume by the first optical sensor and the second optical sensor, respectively, after which the rotational velocity in the second rotational direction is reduced until the presence of the laundry is detected only in the second quarter again by the second optical sensor.

[0053] In an embodiment the dryer further comprises a first humidity sensor, at or near the air inlet, that is operationally connected to the control unit for sending a first signal with a value indicative of a first humidity of the air flowing into the drum to the control unit and a second humidity sensor, at or near the air outlet, that is operationally connected to the control unit for sending a second signal with a value indicative of a second humidity of the air flowing out of the drum to the control unit, wherein the method comprises the step of ending the drying when the value of the second signal is equal and remains equal to the value of the first signal despite increases in the rotational velocity.. According to an alternative embodiment the method comprises the step of ending the drying when the value of the second signal is lower than or equal to and remains lower than or equal to the value of a predetermined humidity for dried laundry despite increases in the rotational velocity. In general, the drying is ended when the value of the second signal reaches a value indicative of a predetermined humidity for dried laundry, which is in the range of 100% to 250% of the value of the first signal.

[0054] The aforementioned method and its dependent aspects have the same advantages as the corresponding aspects of the dryer according to the first aspect of the invention and will not be repeated hereafter.

[0055] The various aspects and features described and shown in the specification can be applied, individually, wherever possible. These individual aspects, in particular the aspects and features described in the attached dependent claims, can be made subject of divisional patent applications.

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The invention will be elucidated on the basis of an exemplary embodiment shown in the attached schematic drawings, in which:

figure 1 shows a side view of a tumble dryer according to the invention;

figure 2 shows a front view of the tumble dryer according to figure 1;

figures 3A, 3B and 3C show graphs of the operation of the tumble dryer according to figures 1 and 2, during an incremental drying mode;

figures 4A, 4B and 4C show graphs of the operation of the tumble dryer according to figures 1 and 2, during a dehumidification mode mode; and

figures 5A and 5B show graphs of the operation of the tumble dryer according to figures 1 and 2, during an alternatively configured drying mode.

DETAILED DESCRIPTION OF THE INVENTION

[0057] Figures 1 and 2 show a tumble dryer 1 for drying wet laundry 9 according to an exemplary embodiment of the invention.

[0058] The tumble dryer 1 comprises a housing 2, a drum 3 rotatably arranged within the housing 2 and a drum motor 4 for rotating the drum 3 around a horizontally extending rotational axis R with an adjustable rotational velocity (RPM). The housing 2 comprises a front face 20 and a back or rear face 21. The front face 20 is provided with a door 22 for loading the laundry 9 into the drum 3. The exemplary tumble dryer 1 is thus a front loader. The invention may however also be applied to a top loader tumble dryer (not shown).

[0059] As shown in figure 2, the drum 3 comprises a substantially cylindrical circumferential wall 30 that encloses a cylindrical drum volume V for receiving the laundry 9. The circular cross section of the drum volume V can be virtually or fictitiously divided into a bottom half 31 and a top half 32. The top half 32 can be further virtually or fictitiously divided into a first or left quarter 33 and a second or right quarter 34. The drum 3 is rotatable by the drum motor 4 in a clockwise and counter-clockwise direction, when viewing from the front of the dryer 1, at the side of the front face 20. Analogously to the clockwise direction, the radial directions within the drum volume V can be compared to the hours of the clock, 12 o'clock being the vertical direction towards the top and 6 o'clock being the vertical direction towards the bottom of the drum volume V. In this respect, the top half 32 of the drum volume V extends from 9 o'clock to 3 o'clock, with the first quarter 33 extending from 9 o'clock to 12 o'clock and the second quarter 34 extending from 12 o'clock to 3 o'clock.

[0060] As shown in figure 1, the tumble dryer 1 further comprises an air inlet 51 and an air outlet 52 arranged in flow communication with the drum volume V of the drum 3. In this exemplary embodiment, the air inlet 51 is arranged at the rear face 21 of the housing 2. The air outlet 52 is arranged at the front face 20 and extends around the door 22. The tumble dryer 1 is provided with an air flow generator 6 for generating an air flow F with an adjustable flow rate FR into the drum 3 though the air inlet 51 (see arrow A) and out of the drum through the air outlet 52 (see arrow B). In this exemplary embodiment, the air flow generator 6 is placed upstream of the drum 3, preferably at or near the air inlet 51. The air flow generator 6 is thus arranged for blowing air into the drum 3. The number and/or positions of the air inlet(s) 51 and the air outlet(s) 52 may be varied to obtain an optimal air flow F through the drum.

[0061] The tumble dryer 1 is arranged to be placed in a naturally ventilated room (not shown). The air inlet 51 is arranged for drawing in air directly from the room. The typical relative humidity in a naturally ventilated room is between 40 and 60%. The air flowing into the drum 3 (arrow A) therefore has a variable first relative humidity RV1 equal to the relative humidity in the room. The air outlet 52 is arranged for discharging air out the drum 3 directly into the room (see arrow B) in which the dryer 1 is placed. The water that is being extracted from the wet laundry 9 during the drying of the laundry 9 contributes to a second relative humidity RV2, usually higher than the first relative humidity RV1, in the air that is discharged from the drum 3 into the room (see arrow B). This increases the relative humidity in the room. For comfortable or habitable conditions, the relative humidity in the room is still acceptable up to approximately 65 or 70%.

[0062] The air flow generator 6 is capable of generating a flow rate (FR) in the range of 600 to 1600 times the drum volume V per hour. In this example, the drum volume V is approximately 1 cubic meter, and thus the flow rate (FR) ranges from 600 cubic meters to 1600 cubic meters per hour. Preferably, the air flow generator 6 operates with a flow rate (FR) of at least 800 cubic meters per hour. The air flow generator 6 is placed upstream of the drum 3, preferably at or near the air inlet 51. In this exemplary embodiment, the air flow generator 6 is a ventilator or a blower. To increase the maximum flow rate FR, multiple air flow generators and/or multiple air inlets may be used (not shown).

[0063] The tumble dryer 1 is provided with a plurality of sensors 7 and a control unit 8 that is operationally and/or electrically connected to the drum motor 4, the air flow generator 6 and the plurality of sensors 7 for controlling the drum motor 4 and the air flow generator 6 based on the signals received from the plurality of sensors 7. The plurality of sensors 7 comprises a first humidity sensor 71 that is placed at, near or in the air inlet 51 and that is arranged for sending a first signal with a value indicative of the first relative humidity RV1 of the air flowing into the drum 3 (see arrow A) to the control unit 8. The plurality of sensors 7 further comprises a second humidity sensor 72 that is placed at, near or in air outlet 52 and that is arranged for sending a second signal with a value indicative of the second relative humidity RV2 of the air flowing out of the drum 3 (see arrow B) to the control unit 8.

[0064] In addition to the humidity sensors 71, 72, the plurality of sensors 7 optionally comprises a first optical sensor 73 and a second optical sensor 74 for detecting presence of the laundry 9 in the first quarter 33 and the second quarter 34, respectively, of the upper half 32 of the drum volume V. Specifically, the first optical sensor 73 and the second optical sensor 74 are arranged in a position with respect to the drum volume V in which the first optical sensor 73 and the second optical sensor 74 detect the presence of the laundry 9 only within the radially outer 10% of the diameter D of the drum volume V. In this example, the first optical sensor 73 is arranged for detecting the presence of the laundry 9 between the 10 o'clock and 11 o'clock position with respect to the drum volume V. The second optical sensor 74 is arranged for detecting the presence of the laundry 9 between the 1 o'clock and 2 o'clock position with respect to the drum volume V.
Finally, the plurality of sensors 7 also optionally comprises a temperature sensor 75 at, near or in the air inlet 51 for sending a third signal with a value indicative of a temperature T of the air flowing into the drum 3 (see arrow A) to the control unit 8.

[0065] The method for drying the wet laundry 9 with the use of the aforementioned tumble dryer 1 will be elucidated below with reference to figures 1, 2, 3A-3C and 4A-4C.

[0066] Figures 3A-3C and figures 4A-4C show graphs schematically representing the values as derived from the signals received by the control unit 8 from the plurality of sensors 7. The vertical axes set out the respective amounts of the values (rotational velocity RPM, flow rate FR and relative humidity RV) versus time (t) on the horizontal axes. Based on these values, the control unit 8 controls the modes in which the tumble dryer 1 operates. The modes will be described in more detail below.

[0067] Figures 3A-3C show the operation of the tumble dryer 1 according to the invention in a 'drying mode'. The control unit 8 is arranged for starting the drying mode when the value RV1 of the first signal (representative of the first relative humidity RV1 of the air flowing into the drum 3 via the air inlet 51, see arrow A in figure 1) is below a preset lower humidity limit RV-min. The lower humidity limit RV-min may be preset to a relative humidity that is preferential for drying, e.g. 60% or less, or 50% or less. As shown in figure 3C, at t0, the value RV1 of the first signal is still above the preset lower humidity limit RV-min. At t1, the value RV1 of the first signal drops below the preset lower humidity limit RV-min and the 'drying mode' is initiated.

[0068] At the start of the 'drying mode', at t1, the drum motor 4 (figure 1) is controlled to start rotating at a preset lower velocity limit RPM-min, as shown in figure 3A, and the air flow generator 6 (figure 1) is arranged to start providing a substantially constant flow rate (FR), e.g. of approximately 800 cubic meters per hour. As the laundry 9 is still relatively wet at the start of the 'drying mode', a lot of moisture or water will be extracted from the laundry 9 and discharged in the air flowing out of the drum 3. As a result, the value RV2 of the second signal (representative of the second relative humidity RV2 of the air flowing out of the drum 3 via the air outlet 52, see arrow B in figure 1) will immediately increase and ultimately stabilize due to the cohesion of the water in the laundry 9, as shown in figure 3C. As long as the value RV2 of the second signal does not decrease, the rotational velocity (RPM) is kept stable or substantially constant. However, as soon as the value RV2 of the second signal starts to decrease, in this case at t2, the control unit 8 increases the rotational velocity (RPM) of the drum 3 with a first increment C1 to force more water out of the laundry 9 at the higher rotational velocity (RPM), as shown in figure 3A. Again, the value RV2 of the second signal will start to increase, as shown in figure 3C. The rotational velocity (RPM) is incrementally increased for each time t3, t4, t5, t6 that the value RV2 of the second signal starts to decrease.

[0069] The rotational velocity (RPM) cannot be increased infinitely and is limited in range by the specifications of the drum motor 4, the control unit 8 or user preference.

[0070] Hence, in one embodiment of the invention, the control unit 8 is provided with a preset upper velocity limit RPM-max in addition to the preset lower velocity limit RPM-min. In the 'drying mode', the control unit 8 is arranged for incrementally increasing the rotational velocity (RPM) in cycles from the preset lower velocity limit RPM-min towards the preset upper velocity limit RPM-max, as shown schematically by increments C1-C5 in figure 3A, until the rotational velocity (RPM) reaches the preset upper velocity limit RPM-max. The control unit 8 subsequent reduces the rotational velocity (RPM) to the preset lower velocity limit RPM-min. Per cycle, the maximum value RV2 reached by the second signal gradually decreases as less and less water is extracted from the laundry 9. The value RV2 of the second signal initially reaches 80 percent relative humidity, but gradually decreases to the same level as the value RV1 of the first signal. The control unit 8 is arranged for ending the 'drying mode' when the value RV2 of the second signal no longer increases as a result of the increments C1-C5 in the rotational velocity (RPM), or when the value RV2 of the second signal remains equal to the value RV1 of the first signal despite the increments C1-C5 in the rotational velocity (RPM) during the 'drying mode'. Both are indicative of the laundry 9 being as dry or approaching the dryness of the relative humidity in the room, which is considered sufficiently dry.

[0071] In an alternative embodiment for controlling the range of the rotational velocity (RPM), the control unit 8 is arranged for resetting the increment cycle C1-C5 as soon as the laundry 9 is optically detected by both optical sensors 73, 74. This is an indication that the laundry 9 has lost water and has become so light-weight that is does no longer fall or tumble through the center of the drum 3. Instead, the laundry 9 passes in front of optical sensor 73, 74 that is the furthest in the rotational direction R1, R2 of the drum 3. The control unit 8 reduces or resets the rotational velocity (RPM) to or towards the lower velocity limit RPM-min until the laundry 9 is again only detected by one of the optical sensors 73, 74.

[0072] Throughout the 'drying mode', the flow rate (FR) is kept substantially constant, as shown in figure 3B. Alternatively, the flow rate (FR) may be incrementally increased together with each incremental increase C1-C5 in the rotational velocity (RPM) as shown in figure 3A.

[0073] As long as the laundry 9 is still relatively wet, the second relative humidity RV2 of the air flowing out of the drum 3 (see arrow B in figure 1) during the 'drying mode' is considerably higher than the relative humidity RV1 of the air flowing into the drum 3 (see arrow A in figure 1). The air that is discharged from the tumble dryer 3 mixes again with the air in the room as it reenters the room and contributes to the relative humidity in said room. Consequently, the first relative humidity RV1 of the air that is being drawn in via the air inlet 51 into the drum 3 (see arrow A in figure 1) from the same room gradually increases. Thus, a situation may be created in which the air in the room has a relative humidity that is no longer acceptable or habitable.

[0074] Figures 4A-4C show the operation of the tumble dryer 1 according to the invention when the 'drying mode' is interrupted by a 'dehumidification mode' to prevent the relative humidity in the room reaching unacceptable levels. The tumble dryer 1 is controlled by the control unit 8 in the same way as shown in figures 3A-3C. The control unit 8 will continue to incrementally increase the rotational velocity (RPM) of the drum 3, as shown with increments C1-C5 in figure 4A, unless the value RV1 of the first signal reaches a preset upper humidity limit RV-max, as shown in figure 4C. The preset upper humidity limit RV-max is set to the still acceptable relative humidity for the room, e.g. in the range of 60% to 70% relative humidity. As soon as the value RV1 of the first signal reaches the preset upper humidity limit RV-max, in this case at t2, the rotational velocity (RPM) of the drum 3 is reduced, preferably by at least half of the rotational velocity (RPM) prior to t2, or the rotation of the drum 3 is stopped completely. In addition, the flow rate (FR) is reduced, preferably by at least half of the flow rate (FR) prior to t2.

[0075] The sudden decrease in rotational velocity (RPM) and the flow rate (FR) significantly reduces the water being extracted from the laundry 9 and thus the second relative humidity RV2 of the air flowing out of the drum 3 (see arrow B in figure 1). Consequently, the value RV2 of the second signal drops abruptly and the value RV1 of the first signal is allow to stabilize and subsequently decrease to below the preset lower humidity limit RV-min, as shown in figure 3C. At that moment, in this case at t3, the control unit 8 switches back to 'drying mode' and the operation of the tumble dryer 1 in the 'drying mode' is resumed as described above.

[0076] The control unit 8 is optionally configured for, based on the value of the third signal (representative of the temperature of the air flowing into the drum 3, see arrow A in figure 1) setting the setting the preset lower humidity limit RV-min and/or the preset upper humidity limit RV-max. For example, when the temperature of the air flowing into the drum 3 (arrow A) is relatively high, e.g. above 25 degrees Celsius, the preset lower humidity limit RV-min and/or the preset upper humidity limit RV-max may be set higher than in a situation when the temperature of the air flowing into the drum 3 (arrow A) is relatively low, e.g. below 18 degrees Celsius. The high temperature of the air in combination with the relatively high relative humidity RV1 may still provide acceptable drying performance, while in lower temperatures, the drying performance is to a large extent dependent on a relatively low relative humidity RV1.

[0077] In an alternative configuration of the tumble dryer 1, the increase of the rotational velocity (RPM) in the 'drying mode' is controlled based on the optical detection signals from the first optical sensor 73 and the second optical sensor 74, as schematically represented by the digital signals OD1 and OD2 in the graph of figure 5B.

[0078] In the alternative configuration of the tumble dryer 1, the drum motor 4 is arranged for rotating the drum 3 alternatingly in a first, clockwise rotational direction R1 and a second, counter-clockwise rotational direction R2, as shown in figures 1 and 2. At the start of the 'drying mode', the control unit 8 is arranged for rotating the drum 3 in the first rotational direction R1 while increasing the rotational velocity from a preset lower velocity limit RPM-min, as shown in figure 5A, until the presence of the laundry 9 is detected in only the first quarter 33 by the first optical sensor 73. The detection signal OD1 of the first optical sensor 73 is shown as a digital signal at t1 in the graph of figure 5B. Although the detection signal OD1 is depicted as being constant throughout the detection, in practice, it will be random and/or intermittent, depending on the distribution of the laundry 9 within the drum 3. Upon detection, the control unit 8 controls the drum motor 4 so that the drum 3 rotates at a constant or substantially constant rotational velocity (RPM) in the first rotational direction R1. The laundry 9 now constantly tumbles or falls down in front of or in the detection range of the first optical sensor 73, while the laundry 9 is not being detected by the second optical sensor 74. This is indicative of a situation in which the laundry 9 falls down through the center of the drum 3, in the area between the positions of the first optical sensor 73 and the second optical sensor 73. As the laundry 9 loses water, it will be become lighter. As a result, the laundry 9 will be carried further by the rotation of the drum 3 before tumbling or falling down. Ultimately, the laundry 9 will start falling down in front or in the viewing range of the second optical sensor 74 in the second quarter 34. The detection signal OD2 of the second optical sensor 74 is shown as a digital signal at t2 in the graph of figure 5B.

[0079] As soon as the control unit 8 receives detection signals OD1, OD2 from both the first optical sensor 73 and the second optical sensor 74, the control unit 8 reduces rotational velocity (RPM) in the first rotational direction R1 in a first decrement E1. The laundry 9 starts to lose momentum and will tumble or fall down again before reaching the second optical sensor 74. The control unit 8 reduces the rotational velocity (RPM) until the presence of the laundry 9 is detected only in the first quarter 33 again by the first optical sensor 73, as shown at t3 in figures 5A and 5B. The control unit 8 subsequently keeps the rotational velocity (RPM) in the first rotational direction R constant until the laundry 9 again loses enough water to become light enough to pass in front of both the first optical sensor 73 and the second optical sensor 74.

[0080] The control unit 8 is arranged for periodically alternating the rotational of the drum 9 between the first rotational direction R1 and the second rotational direction R2, for example when reaching a preset lower velocity limit RPM-min as shown in figure 5A. The above process is repeated for the second rotational direction R2, in which case the second optical sensor 74 detects the laundry 9 first and the first optical sensor 73 is indicative of the laundry 9 becoming light and passing in front of the first optical sensor 73.

[0081] The aforementioned, alternatively configured 'drying mode' is continued until the laundry 9 is sufficiently dry. The first humidity sensor 71 and the second humidity sensor 72 can either be eliminated or are solely used for determining the dryness of the laundry 9 by comparing the value RV2 of the second humidity sensor 72 to the value RV1 of the first humidity sensor 71. The control unit 8 is arranged for ending the alternatively configured 'drying mode' when the value RV2 of the second signal no longer increases as a result of increases in the rotational velocity (RPM), or when the value RV2 of the second signal remains equal to the value RV1 of the first signal despite increases in the rotational velocity (RPM) during the 'drying mode'. Both are indicative of the laundry 9 being as dry or approaching the dryness of the relative humidity in the room, which is considered sufficiently dry.

[0082] It is to be understood that the above description is included to illustrate the operation of the preferred embodiments and is not meant to limit the scope of the invention. From the above discussion, many variations will be apparent to one skilled in the art that would yet be encompassed by the scope of the present invention.

[0083] In summary, the invention relates to a dryer 1 and a method for drying wet laundry 9, wherein the dryer 1 comprises a drum 3, a drum motor 4, an air inlet 51, an air outlet 52 and an air flow generator 6, wherein the dryer 1 further comprises a control unit 8 for controlling the rotational velocity (RPM) and the flow rate (FR), wherein the volume of the drum 3 is divided into an upper half 32 and a lower half 31, wherein the upper half 32 is divided into a first quarter 33 and a second quarter 34 downstream of the first quarter in the first rotational direction R1, wherein the dryer 1 is provided with a first optical sensor 73 and a second optical sensor 74 for detecting presence of the laundry in the first quarter and the second quarter, respectively, of the upper half of the drum volume V, wherein the control unit 8 is arranged for rotating the drum 3 in the first rotational direction R1 while increasing the rotational velocity in the drying mode from a preset lower velocity limit RPM-min until the presence of the laundry is detected only in the first quarter by the first optical sensor 73, wherein the control unit 8 is arranged for subsequently keeping the rotational velocity substantially constant until the presence of the laundry is detected in both the first quarter and the second quarter of the drum volume by the first optical sensor 73 and the second optical sensor 74, respectively, after which the control unit 8 is arranged for reducing the rotational velocity in the first rotational direction R1 until the presence of the laundry is detected only in the first quarter again by the first optical sensor 73.

[0084] It is clear that, although embodiments as described above, which make use of unheated and/or variably humid air are advantageous, alternative embodiments of dryers which make use of heated air or air with a controlled humidity are also possible.

Claims

1. Dryer, in particular a tumble dryer, for drying wet laundry, comprising a drum for receiving the wet laundry, a drum motor for rotating the drum at an adjustable rotational velocity in a first rotational direction, an air inlet and an air outlet arranged in flow communication with the drum, and an air flow generator for generating an airflow with an adjustable flow rate into the drum though the air inlet and out of the drum through the air outlet, wherein the dryer further comprises a control unit that is operationally connected to the drum motor and the air flow generator for controlling the adjustable rotational velocity and the adjustable flow rate, respectively, wherein the volume of the drum is divided into an upper half and a lower half, wherein the upper half is divided into a first quarter and a second quarter downstream of the first quarter in the first rotational direction, wherein the dryer is provided with a first optical sensor and a second optical sensor for detecting presence of the laundry in the first quarter and the second quarter, respectively, of the upper half of the drum volume, wherein the control unit is arranged for rotating the drum in the first rotational direction while increasing the rotational velocity in the drying mode from a preset lower velocity limit until the presence of the laundry is detected only in the first quarter by the first optical sensor, wherein the control unit is arranged for subsequently keeping the rotational velocity substantially constant until the presence of the laundry is detected in both the first quarter and the second quarter of the drum volume by the first optical sensor and the second optical sensor, respectively, after which the control unit is arranged for reducing the rotational velocity in the first rotational direction until the presence of the laundry is detected only in the first quarter again by the first optical sensor.

2. Dryer according to claim 1, wherein the drum motor is arranged for rotating the drum in a second rotational direction opposite to the first rotational direction, wherein the control unit is arranged for rotating the drum alternatingly in the first rotational direction and the second rotational direction, wherein, when rotating the drum in the second rotational direction, the control unit is arranged for increasing the rotational velocity in the second rotational direction from the preset lower velocity limit until the presence of the laundry is detected only in the second quarter by the second optical sensor, wherein the control unit is arranged for subsequently keeping the rotational velocity substantially constant until the presence of the laundry is detected in both the first quarter and the second quarter of the drum volume by the first optical sensor and the second optical sensor, respectively, after which the control unit is arranged for reducing the rotational velocity in the second rotational direction until the presence of the laundry is detected only in the second quarter again by the second optical sensor.

3. Dryer according to claim 1 or 2, wherein the first optical sensor and the second optical sensor are arranged for detecting the presence of the laundry within the radially outer 10% of the diameter of the drum volume.

4. Dryer according to any of the preceding claims, wherein the first optical sensor is arranged, referring to the hours of a clock, for detecting the presence of the laundry between the 10 o'clock and 11 o'clock position with respect to the drum volume, wherein the second optical sensor is arranged, again referring to the hours of a clock, for detecting the presence of the laundry between the 1 o'clock and 2 o'clock position with respect to the drum volume.

5. Dryer according to any of the preceding claims, wherein the dryer further comprises a first humidity sensor, at or near the air inlet, that is operationally connected to the control unit for sending a first signal with a value indicative of a first humidity of the air flowing into the drum to the control unit and a second humidity sensor, at or near the air outlet, that is operationally connected to the control unit for sending a second signal with a value indicative of a second humidity of the air flowing out of the drum to the control unit, wherein the control unit is arranged for ending the drying mode:

- when the value of the second signal is equal and remains equal to the value of the first signal despite the increases in the rotational velocity; and/or

- when the value of the second signal is lower than or equal to and remains lower than or equal to the value of a predetermined humidity for dried laundry despite increases in the rotational velocity; and/or

- when the value of the second signal reaches a value indicative of a predetermined humidity for dried laundry, which is in the range of 100% to 250% of the value of the first signal.

6. Dryer according to any one of the preceding claims, wherein the air flow generator has a flow rate capacity in the range of 600 to 1600 times the volume of the drum per hour, and preferably has a flow rate capacity of at least 600 cubic meters per hour, most preferably 800 cubic meters per hour; and/or

7. Dryer according to any one of the preceding claims, wherein the air flow generator is placed upstream of the drum, preferably at or near the air inlet; and/or

8. Dryer according to any one of the preceding claims, wherein the air flow generator is a ventilator or a blower; and/or

9. Dryer according to any one of the preceding claims, wherein the dryer is arranged for drawing air into the drum via the air inlet from a naturally ventilated room; and/or

10. Dryer according to any one of the preceding claims, wherein the dryer is arranged for drawing ambient, unheated and/or variably humid air into the drum via the air inlet; and/or

11. Dryer according to any one of the preceding claims, wherein the dryer is arranged for discharging air out of the drum through the air outlet into a room in which the dryer is placed, wherein the dryer is further arranged for drawing air into the drum via the air inlet from the same room; and/or

12. Dryer according to any one of the preceding claims, wherein the dryer operates without a heating element for actively heating the air flowing into the drum via the air inlet, or wherein the dryer comprises a heating element that is operationally connected to the control unit.

13. Method for drying wet laundry with the dryer according to any of the preceding claims, wherein the method comprises the steps of rotating the drum in the first rotational direction while increasing the rotational velocity from a preset lower velocity limit until the presence of the laundry is detected only in the first quarter by the first optical sensor, wherein the rotational velocity is kept substantially constant until the presence of the laundry is detected in both the first quarter and the second quarter of the drum volume by the first optical sensor and the second optical sensor, respectively, after which the rotational velocity in the first rotational direction is reduced until the presence of the laundry is detected only in the first quarter again by the first optical sensor.

14. Method according to claim 13, wherein the method comprises the step of rotating the drum alternatingly in the first rotational direction and a second rotational direction, wherein, when rotating the drum in the second rotational direction, the rotational velocity is increased from the preset lower velocity limit until the presence of the laundry is detected only in the second quarter by the second optical sensor, wherein the rotational velocity is kept substantially constant until the presence of the laundry is detected in both the first quarter and the second quarter of the drum volume by the first optical sensor and the second optical sensor, respectively, after which the rotational velocity in the second rotational direction is reduced until the presence of the laundry is detected only in the second quarter again by the second optical sensor.

15. Method according to claim 13 or 14, wherein the dryer further comprises a first humidity sensor, at or near the air inlet, that is operationally connected to the control unit for sending a first signal with a value indicative of a first humidity of the air flowing into the drum to the control unit and a second humidity sensor, at or near the air outlet, that is operationally connected to the control unit for sending a second signal with a value indicative of a second humidity of the air flowing out of the drum to the control unit, wherein the method comprises the step of ending the drying when the value of the second signal is equal and remains equal to the value of the first signal despite increases in the rotational velocity.

Drawing