Abstract:
A clothes dryer capable of providing a dry course suitable for functional clothes, and a control method thereof, the control method including selecting functional clothes as a substance accommodated in a dry tub to be dried; performing a first dry process to dry the functional clothes at a first dry temperature; and performing a second dry process to dry the functional clothes at a second dry temperature higher than the first dry temperature.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2011-0147949, filed on Dec. 30, 2011 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Embodiments of the present disclosure relate to a clothes dryer capable of providing a drying course suitable for functional clothes, and a control method thereof. 
     2. Description of the Related Art 
     A clothes dryer is an apparatus configured to dry a substance to be dried, such as washed clothes, by evaporating moisture contained in the substance. The clothes dryer operates in a hot wind scheme by rotating a dry tub (drum) at an inside a body of the clothes dryer while supplying heated wind to the inside of the dry tub to dry clothes. 
     The clothes dryer is mainly divided into an exhaust-type dryer and a condenser-type dryer. The exhaust-type dryer refers to a dryer to exhaust a high temperature and humidity air passed through the dry tub to the outside the dryer. The condenser-type dryer refers to a dryer to eliminate moisture from high temperature and humid air passed through the dry tub, and circulate the air having moisture removed therefrom into the dry tub again. 
     The clothes dryer provides various dry courses depending to the type of clothes, that is, depending on the type of fabric of the clothes. For example, the dry courses may include a standard course, a towel course, and an underwear course. As such, the clothes dryer provides various dry courses, so a user may be able to dry clothes by selecting a drying course suitable for the type of clothes. 
     However, the conventional clothes dryer as such fails to provide a dry course suitable for functional clothes, such as sportswear and mountaineering sportswear. In many cases, the functional clothes, such as sportswear and mountaineering sportswear, are formed of a moisture penetrating and water repellant material or a stretchy material. The functional clothes passing through a washing process may lose its own characteristic of the fabric, for example water repellant performance. If the functional clothes having the function degraded are dried at a temperature inappropriate for the fabric, the degraded function is not recovered or the shape of the clothes is deformed. Although a clothes dryer providing a dry course for synthetic fiber is present, the dry course for synthetic fiber proceeds at a low temperature unconditionally, thereby having a difficulty in obtaining a desired degree of dryness of the clothes. 
     SUMMARY 
     Therefore, it is an aspect of the present disclosure to provide a clothes dryer capable of providing a dry course suitable for functional clothes, and a control method thereof. 
     Additional aspects of the disclosure will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the disclosure. 
     In accordance with one aspect of the present disclosure, a method of controlling a clothes dryer is as follows. If a substance accommodated in a dry tub to be dried is functional clothes, a first dry process may be performed to dry the substance at a first dry temperature. A second dry process may be performed to dry the substance at a second dry temperature higher than the first dry temperature. 
     The functional clothes may include at least one of a moisture penetrating and water repellant material and a stretchy material. 
     The first dry temperature may be a temperature that recovers a water repellant function of the moisture penetrating and water repellant material. The second dry process may be performed during a second dry time, and the second dry time may be a period of time that prevents the stretchy material from being deformed when the stretch material is exposed to the second dry temperature. 
     The performing of the first dry process may be as follows. More than one heater may be turned on. A temperature at an inside of the dry tub may be maintained at the first dry temperature by repeating turning on and off the more than one heater, if the temperature at the inside of the dry tub reaches the first dry temperature. 
     The maintaining of the temperature at the inside of the dry tub at the first dry temperature may be as follows. A second heater having a power capacity larger than a first heater is turned on and off repeatedly in a state that the first heater is being turned on. 
     The performing of the second dry process may be as follows. An operation temperature of more than one heater may be raised if a degree of dryness of the substance reaches a target degree of dryness in the first dry process. A temperature at an inside of the dry tub may be maintained at the second dry temperature by repeating turning on and off the more than one heater, if the temperature at the inside of the dry tub reaches the second dry temperature. 
     The maintaining of the temperature at the inside of the dry tub at the second dry temperature may be as follows. A second heater having a power capacity larger than a first heater may be turning on and off repeatedly in a state that the first heater is being turned on. 
     In accordance with the present disclosure, a clothes dryer includes a dry tub, and a control unit. The dry tub may be configured to accommodate a substance to be dried. The control unit may be configured to sequentially perform a first dry process to dry the substance at a first dry temperature and a second dry process to dry the substance at a second dry temperature higher than the first dry temperature, if the substance is functional clothes. 
     The functional clothes may include at least one of a moisture penetrating and water repellant material and a stretchy material. 
     The first dry temperature may be a temperature that recovers a water repellant function of the moisture penetrating and water repellant material. The second dry process may be performed during a second dry time, and the second dry time may be a period of time that prevents the stretchy material from being deformed when the stretch material is exposed to the second dry temperature. 
     The control unit may perform the first dry process by turning on more than one heater, and maintaining the temperature at an inside of the dry tub at the first dry temperature by repeating turning on and off the more than one heater, if a temperature at the inside of the dry tub reaches the first dry temperature by the more than one heater. 
     The control unit may maintain the temperature at the inside of the dry tub at the first dry temperature by repeating turning on and off a second heater having a power capacity larger than a first heater in a state that the first heater is being turned on. 
     The control unit may perform the second dry process by raising an operation temperature of more than one heater if a degree of dryness of the substance reaches a target degree of dryness in the first dry process, and maintaining the temperature at an inside of the dry tub at the second dry temperature by repeating turning on and off the more than one heater, if the temperature at the inside of the dry tub reaches the second dry temperature. 
     The control unit may maintain the temperature at the inside of the dry tub at the second temperature by repeating turning on and off a second heater having a power capacity larger than a first heater in a state that the first heater is being turned on. 
     As described above, a dry course suitable for functional clothes is provided, so that the function of the functional clothes degraded while passing through a washing process is recovered. 
     In a case of functional clothes being dried according to a dry course suitable for the functional clothes, when compared to a dry course that unconditionally proceeds with drying, the shape of the functional clothes is prevented from being deformed. 
     In a case of clothes being dried according to a dry course suitable for the clothes, when compared to a dry course that unconditionally proceeds with drying, an improved degree of dryness is obtained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects of the disclosure will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a perspective view illustrating a clothes dryer in accordance with one embodiment of the present disclosure. 
         FIG. 2  is a cross sectional view illustrating of the clothes dryer of  FIG. 1 . 
         FIG. 3  is a control block diagram of the clothes dryer in accordance with one embodiment of the present disclosure. 
         FIG. 4  is a graph showing the change in temperature at an inside a dry tub according to the time in a case that a particular material course is selected in the clothes dryer of  FIG. 3 . 
         FIG. 5  is a flow chart illustrating a control process of the clothes dryer in accordance with one embodiment of the present disclosure. 
         FIG. 6  is a control block diagram of a clothes dryer in accordance with another embodiment of the present disclosure. 
         FIG. 7  is a graph showing the change in temperature at an inside a dry tub according to the time in a case that a particular material course is selected in the clothes dryer of  FIG. 6 . 
         FIG. 8  is a flow chart illustrating a control process of the clothes dryer of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
       FIG. 1  is a perspective view illustrating a clothes dryer in accordance with one embodiment of the present disclosure.  FIG. 2  is a cross sectional view illustrating the clothes dryer of  FIG. 1 . 
     Referring to  FIGS. 1 and 2 , a clothes dryer  1  in accordance with one embodiment of the present disclosure includes a body  10 , a dry tub  20 , a drying apparatus  30 , and a hot air duct  70 . 
     The body  10  is provided in an approximately hexahedron shape. The body  10  may include a cabinet  11 , a top cover  12  to cover an upper portion of the cabinet  11 , a front side panel  13  disposed at a front of the cabinet  11 , and a control panel  14 . At the control panel  14 , an input unit ( 110  in  FIG. 3 ) and a display unit ( 140  in  FIG. 3 ) may be disposed. The input unit  110  may include various buttons to control the clothes dryer  1 . The display unit  140  may display the status of operation of the clothes dryer  1 . The input unit  110  may be separately implemented from the display unit  140  in a hardware aspect, and may be implemented as an integrated form, such as a touch screen, in a hardware aspect. 
     The dry tub  20  is a space where a substance is dried, and the dry tub  20  is rotatably installed at an inside of the body  10 . The dry tub  20  is provided in the form of a cylinder having a front surface and a rear surface thereof open. At an inside of the dry tub  20 , a plurality of lifters  21  is provided to lift and drop the substance. At an inner side of a front surface portion of the body  10 , a front side support panel  22  is installed, and at an inner side of a rear surface portion of the body  10 , a rear side support panel  24  is installed. The front side support panel  22  and the rear side support panel  24  support a front side opening and a rear side opening of the dry tub  20 , respectively, so that the dry tub  20  is rotated. A dry tub air intake port  24   a  is formed at an upper portion of the rear side support panel  24 . 
     An inlet  19   a  is formed at the front surface of the body  10  and the front side support panel  22  to allow the substance to be introduced and withdrawn to/from the inside of the dry tub  20 . A door  19  is installed at the front surface of the body  10  to open and close the inlet  19   a.    
     The driving apparatus  30  includes a driving motor  31 , a pulley  32  and a rotating belt  33 . The driving motor  31  is installed at a lower portion at the inside of the cabinet  10 . The pulley  32  and the rotating belt  33  serve to deliver a driving force of the driving motor  31  to the dry tub  20 . The pulley  32  is coupled to the outer surface of the dry tub  20  and a shaft of the driving motor  31 . The rotating belt  33  is installed to be wound around the pulley  32 . 
     The hot air duct  70  may include a heating unit  80  and a hot air supply unit  40 . 
     The heating unit  80  is installed at a lower portion of the dry tub  20  to heat the air being introduced from the outside. The heating unit  80  includes a heater  81  to radiate heat toward the inside of the heating unit  80 . The heater  81  installed at the heating unit  80  may be implemented using a coil heater. The heater may be provided in a plurality thereof. Each of the plurality of heaters may have a different power capacity. For example, when assumed that the total power capacity is 5.3 kW (100%), a heater having a smaller power capacity of about 1.6 kW (30%) and a heater having a larger power capacity of about 3.7 kW (70%) may be used. In this case, the ratio of the heater having a smaller capacity to the heater having a larger capacity is not limited to 3:7, and may vary in accordance with embodiments of the present disclosure. Hereinafter, for the convenience of description, the heater having a smaller power capacity is referred to as ‘a first heater’, and the heater having a larger power capacity is referred to as ‘a second heater’. 
     The hot air supply unit  40  forms an air passage by connecting the heating unit  80  to the dry tub intake port  24   a  formed at the upper portion of the rear side support panel  24 . The hot air supply unit  40  serves to guide air, being heated by the heating unit  80 , to the dry tub  20 . 
     Meanwhile, an exhaust duct  50  is connected to a lower portion of the front side of the dry tub  20 . The exhaust duct  50  serves to guide air of inside of the dry tub  20  to be exhausted to the outside. The exhaust duct  50  includes a front side exhaust duct  51  and a rear side exhaust duct  53 . 
     The front side exhaust duct  51  connects an exhaust port  22   b  installed at a lower portion of the front side support panel  22  to an entry of a blower apparatus  60  installed at a lower portion of the dry tub  20 . A filter member  55  is installed at the front side exhaust duct  51 . The filter member  55  filters foreign substance, such as dust or lint, included in the hot air being discharged from the dry tub  20 . 
     The rear side exhaust duct  53  is installed at a lower portion of the cabinet  11 , and allows an exit of the blower apparatus  60  to communicate with the outer side of a rear surface portion of the cabinet  11 . 
     The blower apparatus  60  includes a blower fan  61  and a blower case  63 . The blower fan  61  is installed at a front side of a lower portion of the dry tub  20  to circulate air. The blower case  63 , while surrounding the blower fan  61 , is connected to the front side exhaust duct  51  and the rear side exhaust duct  53 . 
     A dryness sensor  90  is installed at a lower end portion of the front surface of the dry tub  20 . The dryness sensor  90  makes contact with the substance to be dried at the dry tub  20  as the dry tub  20  rotates, and senses the amount of moisture contained in the substance. An output value of the dryness sensor  90  is used to the degree of dryness of the substance. In detail, the output value being output from the dryness sensor  90  varies depending on the amount of moisture contained in the substance. By comparing an output vale being output from the sensor  90  with an output value stored in advance, the degree of dryness may be determined. To this end, the dryness sensor  90  may include a touch sensor provided in the form of a plate bar. 
     A temperature sensor  95  is installed at a lower end portion of the rear surface of the dry tub  20 . The temperature sensor  95  may sense the temperature of air inside the dry tub  20 . 
       FIG. 3  is a control block diagram of the clothes dryer in accordance with one embodiment of the present disclosure. 
     Referring to  FIG. 3 , the clothes dryer  1  in accordance with one embodiment of the present disclosure includes the dryness sensor  90 , the temperature sensor  95 , the input unit  110 , the control unit  120 , a driving unit  130 , the driving motor  31 , the first heater  81 , the second heater  82 , the dry tub  20 , the blower fan  61  and the display unit  140 . 
     The dryness sensor  90  makes contact with the substance of the inside of the dry tub  20  to sense the amount of moisture being contained in the substance. An output value of the dryness sensor  90  depending on the result of sensing is transmitted to the control unit  120 . 
     The temperature sensor  95  senses the temperature of air of the inside of the dry tub  20 . An output value of the temperature sensor  95  depending on the result of sensing is transmitted to the control unit  120 . 
     The input unit  110  is received with a command to control the operation of the clothes dryer  1 . To this end, the input unit  110  may include various buttons. For example, a dry mode selection button to select one of a manual dry or an automatic dry, a number button to select the temperature or the time for drying the substance in a case when the manual dry is selected, and a dry course selection button to select a dry course in a case when the automatic dry is selected. The dry course includes a standard course, a towel course, an underwear course, a synthetic fiber course and a particular material course. 
     The standard course is a dry course suitable for a general dry, and the towel course is a dry course to dry a towel or a substance formed of cotton at a high temperature. The underwear course is a dry course suitable for drying a thin fabric such as underwear, and the synthetic fiber course is a dry course suitable for drying a substance formed of synthetic fiber. The particular material course is a dry course suitable for functional clothes formed of a particular material, such as a moisture penetrating and water repellent material or a stretch material. The time and temperature for drying may be set to be different at each course. 
     The various buttons provided at the input unit  110  may include at least one of a press-in type button and a rotation type button. For example, the dry mode selection button or the number button may be implemented as a press-in type button, and the dry course selection button may be implemented as a rotation type button. 
     A jog dial may be provided at the input unit  110  besides the buttons described above, to select a state of dryness. The state of dryness may include a semi-drying and a full-drying. 
     The control unit  120  generates a control signal according to a command being input through the input unit  110 , and controls the overall operation of the clothes dryer  1  according to the generated control signal. For example, if a standard course is selected among the dry courses in accordance with the type of the substance, the control unit  120  measures the degree of dryness of the substance through the dryness sensor  90 , and perform a dry process during a predetermined period of time for drying while adjusting the temperature of drying according to the measured degree of dryness. 
     If the particular material course is selected among the dry courses, the control unit  120  controls the overall operation of the clothes dryer  1  according to an algorithm corresponding to the particular material course. 
     The particular material may refer to a moisture penetrating and water repellant material or a stretch material. The stretch material may refer to fiber or fabric having expansion and contraction, such as polyurethane. The moisture penetrating and water repellant material may refer to material having a membrane formed by extending and heating a teflon based resin, which is strong against heat or chemicals. The membrane has a plurality of small pores that allows interior moisture, such as sweat, to penetrate therethrough while preventing the penetration of exterior water. Since the pore has a size of about 2/10,000 mm, the pore prevents a rain drop having a size of 1 mm at the minimum from penetrating while allowing water vapor having a size of about 4/10,000,000 mm to pass through. The membrane may be referred to as GORE-TEX, a trademark of W.L. Gore and Associates, the inventor of the membrane. 
     When the functional clothes formed of the moisture penetrating and water repellant material is subject to a washing process, the water repellant function may be degraded. If the functional clothes having the water repellant function degraded are dried at a high temperature, the degraded water repellant function may be recovered to some degree. However, in a case that functional clothes including stretchy material are unconditionally dried at a high temperature to recover the water repellant function, the shape of the functional clothes is deformed. 
     Accordingly, when the particular material course is selected, the control unit  120  performs two stages of dry processes each having a different dry temperature. In this manner, the water repellent performance of the functional clothes degraded by the washing process is recovered while minimizing the deformation of the functional clothes if the functional clothes are formed of stretch material. 
     Referring to  FIG. 4 , a control process of the clothes dryer  1  when the particular material course is selected will be described in detail.  FIG. 4  is a graph showing the change in temperature at an inside a dry tub according to the time in a case that the substance is controlled according to the particular material course. 
     If the particular material course is selected, the control unit  120  starts a first dry process. To this end, the control unit  120  turns on the first heater  81  and the second heater  82 . As such, the two heaters  81  and  82  are simultaneously turned on, so that the temperature of the inside of the dry tub  20  rapidly reaches a first dry temperature (T 1 ). Thereafter, the temperature at the inside of the dry tub  20   95  is measured using the temperature sensor, and if the temperature of the inside of the dry tub  20  reaches the first dry temperature (T 1 ), the control unit  120  repeats turning on and off the second heater  82  to maintain the temperature of the inside of the dry tub  20  at the first dry temperature (T 1 ). As shown in  FIG. 4 , the repeated on/off of the second heater  82  enables the temperature of the inside of the dry tub  20  to be maintained at the first dry temperature (T 1 ). Thereafter, the degree of dryness of the substance is measured by use of the dryness sensor  90 , and when the measured degree of dryness reaches a target degree of dryness, the control unit  120  starts a second dry process after passing a first dry time (t 1 ) that is allocated to the first dry process. 
     In order to start the second dry process, the control unit  120  turns on the second heater  82 . If a current state is that the second heat  82  is being turned off in the first dry process, the control unit  120  turns on the second heater  82 . If a current state is that the second heat  82  is being turned on in the first dry process, the control unit  120  starts the second dry process by maintaining the-On state of the second heater  82 . After the second heater  92  is turned on as such, the temperature of the inside of the dry tub  20  is measured using the temperature sensor  95 , and if the temperature of the inside of the dry tub  20  reaches a second dry temperature (T 2 ), the control unit  120  repeats turning on and off the second heater  82  to maintain the second dry temperature (T 2 ). Referring to  FIG. 4 , the repeated on/off of the second heater  82  enables the temperature of inside the dry tub  20  to be maintained at the second dry temperature (T 2 ). 
     If a second dry time (t 2 ) allocated to the second dry process has passed after the second dry process starts, the control unit  120  performs a cooling process. The cooling process is performed by turning off the first heater  81  and the second heater  82 , and operating the blower fan  61 . The ratio of time periods allocated to the first dry process, the second dry process and the cooling process is about 3:1:1 in the total time (t 1 +t 2 +t 3 ), allocated to the particular material course. However, the ratio (t 1 :t 2 :t 3 ) of the first dry time, the second dry time, and the cooling time is not limited thereto, and may vary in according to embodiments. The time (t 2 ) allocated to the second dry process is desired to be shorter than the time (t 1 ) allocated to the first dry process. 
     The driving unit  130  operates the driving motor  31 , the first heater  81  and the second heater  82 , which are related to the operation of the clothes dryer  1 , according to the control signal of the control unit  120 . 
     The blower fan  130  is installed at the front side of the lower portion of the dry tub  20 , to circulate the air. In a case of the cooling process being performed, the first heater  81  and the second heater  82  are turned off, and the blower fan  61  only operates. In this case, the blower fan  61  discharges the high temperature air inside the dry tub  20  to the outside. 
     The display unit  140  may be provided on the control panel  14 . The display unit  140  may display the operation state of the clothes dryer  1 . The display unit  140  may be separately implemented from the input unit  110  in a hardware aspect. Alternatively, the display unit  140  and the input unit  110  may be implemented as an integrated body, such as a touch screen, in a hardware aspect. 
     The storage unit  150  may store algorithms or data needed to control the operation of the clothes dryer  1 . For example, the storage unit  150  may store an algorithm corresponding to each dry course, and data needed to perform a dry process according to each algorithm. The data may include the first dry temperature (T 1 ), the second dry temperature (T 2 ), the first dry time (t 1 ) allocated to the first dry process, the second dry time (t 2 ) allocated to the second dry process, and the cooling time (t 3 ) allocated to the cooling process. In this case, the second dry temperature (T 2 ) may be higher than the first dry temperature (T 1 ). For example, the first dry temperature (T 1 ) may be 61 to 62° C., and the second dry temperature (T 2 ) may be 67° C. The second dry time (t 2 ) may be shorter than the first dry time (t 1 ). For example, the first dry time (t 1 ) may be about 24 minutes, and the second dry time (t 2 ) may be about 8 minutes. The cooling time (t 3 ) may be equal to or shorter than the second dry time (t 2 ). 
     The storage unit  150  to store the algorithm or the data described above may be implemented as a non-volatile memory device, such as a Read Only Memory (ROM), a Random Access Memory (RAM), a Programmable Read Only Memory (PROM), an Erasable Programmable Read Only Memory (EPROM), and a flash memory; a volatile memory device such as a Random Access Memory (RAM); hard disks; or optical disks. However, the storage unit  150  of the present disclosure is not limited thereto, and may be implemented in various forms generally know in the art. 
       FIG. 5  is a flow chart illustrating a control process of the clothes dryer in accordance with one embodiment of the present disclosure. 
     If the particular material course is selected ( 500 ), the control unit  120  starts the first dry process by turning on the first heater  81  and the second heater  82  ( 510 ). Since the first heater  81  and the second heater  82  are simultaneously turned on, the time taken for the temperature of the inside of the dry tub  20  to reach the first dry temperature (T 1 ) is reduced. 
     If the first heater  81  and the second heater  82  are turned on in operation  510 , the temperature of the inside of the dry tub  20  is measured. The control unit  120  determines whether the temperature measured by the temperature sensor  95  reaches the first dry temperature (T 1 ) ( 520 ). 
     If a result of determination in operation  520  is that the temperature at the inside of the dry tub  20  does not reach to the first dry temperature (T 1 ), the control unit  120  keeps monitoring the temperature measured through the temperature sensor  95 . 
     If a result of determination in operation  520  is that the temperature at the inside of the dry tub  20  reaches the first dry temperature (T 1 ), the control unit  120  allows the temperature at the inside of the dry tub  20  to be maintained at the first dry temperature (T 1 ) ( 530 ) by repeating turning on and off the second heater  82  having a larger power capacity. In detail, as a predetermined period of time (t off ) passes after the second heater  82  having been turned on in operation  510  is turned off, the temperature at the inside of the dry tub  20  is lowered to some degree. If so, the control unit  120  turns on the second heater  82  again, and after a predetermined period of time (t on ), the temperature at the inside of the dry tub  120  is raised again. As such, the control unit  120  repeats turning on and off the second heater  82  to control such that the temperature at the inside of the dry tub  20  is maintained at the first dry temperature (T 1 ). By turning on/off the second heater  82  in a state that the first heater  81  is being turned on, the temperature at the inside of the dry tub  20  is rapidly changed when compared to turning on/off the first heater  81 . 
     After operation  530 , the control unit  120  determines whether the degree of dryness of the substance contained in the dry tub  200  reaches to a target degree of dryness, based on the result of measurement of the dryness sensor  90 . 
     If a result of determination in operation  540  is that the degree of dryness measured by the dryness sensor  90  does not reach to the target degree of dryness, the control unit  120  repeats turning on and off the second heater  82  such that the temperature at the inside of the dry tub  20  is maintained at the first dry temperature (T 1 ). 
     If a result of determination in operation  540  is that the degree of dryness measured by the dryness sensor  90  reaches the target degree of dryness, the control unit  120  determines whether a first dry time (t 1 ) elapses after a first dry process starts ( 545 ). 
     If a result of determination in operation  545  is that the first dry time (t 1 ) does not pass after the first dry process starts (NO from operation  545 ), the control unit  120  maintains the temperature at the inside of the dry tub  200  at the first dry temperature (T 1 ) until the first dry time (t 1 ) passes. The reason why the first dry time (t 1 ) needs to wait to pass even after the degree of dryness of the substance reaches the target degree of dryness is to cover inaccuracy of the dryness sensor. That is, when the degree of dryness is measured using the dryness sensor, the measured value may be inaccurate. Accordingly, even if the target degree of dryness is achieved, the first dry process continues until the first dry time passes. 
     If a result of determination in operation  545  is that the first dry time (t 1 ) passes after the first dry process starts (YES from operation  545 ), the control unit  120  raises the operation temperature of the second heater  82  ( 550 ) to start the second dry process. The reason why the operation temperature of the second heater  82  is raised is to raise the temperature at the inside of the dry tub  20  from the first dry temperature (T 1 ) from the first dry temperature (T 1 ) to the second dry temperature (T 2 ). 
     Thereafter, the control unit  120  determines whether the temperature at the inside of the dry tub  20  measured by the temperature sensor  95  reaches the second dry temperature (T 2 ) ( 560 ). 
     If a result of determination in operation  560  is that the temperature at the inside of the dry tub  20  does not reach to the second dry temperature (T 2 ), the control unit  120  keeps monitoring the temperature being measured by the temperature sensor  95 . 
     If a result of determination in operation  560  is that the temperature at the inside of the dry tub  20  reaches the second dry temperature (T 2 ), the control unit  120  controls such that the temperature at the inside of the dry tub  20  is maintained at the second dry temperature (T 2 ) by repeating turning on and off the second heater  82  ( 570 ). 
     After operation  570 , the control unit  120  determines whether a second dry time (t 2 ) allocated to the second dry process passes after the second dry process starts ( 580 ). 
     If a result of determination in operation  580  is that the second dry time (t 2 ) does not pass after the second dry process starts, the control unit  120  controls such that the temperature at the inside of the dry tub  20  is maintained at the second dry temperature (T 2 ) by repeating turning on and off the second heater  82  ( 570 ). 
     If a result of determination in operation  580  is that the second dry time (t 2 ) passes after the second dry process starts, the control unit  120  controls the operation of the clothes dryer  1  such that the cooling process is performed ( 590 ). In the cooling process, the first heater  81  and the second heater  82  are turned off, and only the blower fan  61  operates. By only operating the blower fan  61 , the heat inside the dry tub  20  is discharged to the outside the clothes dryer  1 , so that the temperature at the inside of the dry tub  20  is lowered. 
     Meanwhile, in the process of controlling the clothes dryer  1  as such, the reference temperatures T 1  and T 2  to determine the temperature at the inside of the dry  20  may be different from control temperatures that are output from the control unit  120  to operate one of the two heaters  81  and  82 . 
     For example, although the first dry temperature (T 1 ) used to determine the temperature at the inside of the dry tub  20  in operation  520  of  FIG. 5  has been described as about 61 to 62° C., a first control temperature being output from the control unit  120  to operate the two heaters  81  and  82  may be about 54° C. 
     For example, although the second dry temperature (T 2 ) used to determine the temperature at the inside of the dry tub  20  in operation  560  of  FIG. 5  has been described as about 67° C., a second control temperature being output from the control unit  120  to operate the second heat  82  may be about 55° C. In this case, the information about the first control temperature and the second control temperature may be stored in the storage unit  150 . In this case, the first control temperature and the second control temperature may be stored in the form of a mapping table including the mapping relation between the first dry temperature (T 1 ) and the second dry temperature (T 2 ). 
       FIG. 6  is a control block diagram of a clothes dryer in accordance with another embodiment of the present disclosure. 
     Referring to  FIG. 6 , a clothes dryer in accordance with another aspect of the present disclosure includes the dryness sensor  90 , the temperature sensor  95 , an input unit  210 , a control unit  220 , a driving unit  230 , the driving motor  31 , a third heater  83 , the dry tub  20 , the blower fan  61  and a display unit  240 . The components of the clothes dryer in accordance with another embodiment of the present disclosure except for the third heater  83  have the same configurations as those of the clothes dryer of  FIG. 3 , so the description thereof will be omitted. 
     The clothes dryer shown in  FIG. 6  is different from the clothes dryer shown in  FIG. 3  in the number of heaters. The clothes dryer of  FIG. 6  includes only the third heater  83  while the clothes dryer of  FIG. 3  includes the first heater  81  having a smaller power capacity and the second heater  82  having a larger power capacity. 
     The third heater  83  has a power capacity that is equal to or larger than that of the second heater  82  of  FIG. 3 . 
     The control unit  220 , if the particular material course is selected among the dry courses according to the type of substance, performs two stages of dry courses each having a different dry temperature. Hereinafter, the control process of the clothes dryer when the particular material course is selected will be described with reference to  FIG. 7 .  FIG. 7  is a graph showing the change in temperature at an inside of the dry tub  20  according to the time in a case that the drying of the substance is controlled according to the particular material course. 
     If the particular material course is selected, the control unit  220  starts a first dry process. To this end, the control unit  220  turns on the third heater  83 . Thereafter, the temperature at the inside of the dry tub  20  is measured by the temperature sensor  95 , and if determined that the temperature at the inside of the dry tub  20  reaches the first dry temperature (T 1 ), the control unit  220  maintains the first dry temperature (T 1 ) by repeating turning on and off the third heater  83 . As shown in  FIG. 7 , the temperature at the inside of the dry tub  20  is shown to be maintained at the first dry temperature (T 1 ) as the third heater  83  is repeated between on and off. The degree of dryness of the substance is measured by the dryness sensor  90 , and if a result of measurement is that a degree of dryness of the substance reaches a target degree of dryness, the control unit  220  starts a second dry process after a first dry time (t 1 ) allocated to the first dry process. 
     In order to start the second dry process, the control unit  220  raises the operation temperature of the third heater  83 . Thereafter, the temperature at the inside of the dry tub  20  is measured by the temperature sensor  95 , and if the temperature at the inside of the dry tub  20  reaches a second dry temperature (T 2 ), the control unit  220  repeats turning on and off the third heater  83  to maintain the temperature of the inside of the dry tub  20  at the second dry temperature (T 2 ). As shown in  FIG. 7 , the temperature at the inside of the dry tub  20  is shown to be maintained at the second dry temperature (T 2 ) as the third heater  83  is repeated between on and off. 
     If a second dry time (t 2 ) allocated to the second dry process passes after the second dry process start, the control unit  220  performs a cooling process. The cooling process is performed by turning off the third heater  83 , and operating the blower fan  61 . 
       FIG. 8  is a flow chart illustrating a control process of the clothes dryer of  FIG. 6 . 
     If the particular material course is selected ( 800 ), the control unit  220  turns on the third heater  83  to start the first dry process ( 810 ). 
     If the third heater  83  is turned on in operation  810 , the temperature at the inside of the dry tub  20  is measured by the temperature sensor  95 . The control unit  220  determines whether the temperature being measured by the temperature sensor  95  reaches the first dry temperature (T 1 ) ( 820 ). 
     If a result of determination in operation  820  is that the temperature at the inside of the dry tub  20  does not reach to the first dry temperature (T 1 ), the control unit  220  keeps monitoring the temperature measured by the temperature sensor  95 . 
     If a result of determination in operation  820  is that the temperature at the inside of the dry tub  20  reaches the first dry temperature (T 1 ), the control unit  220  maintains the temperature at the inside of the dry tub  20  at the first dry temperature (T 1 ) by repeating turning on and off the third heater  83  ( 830 ). In detail, the third heater  83  having been turned on in operation  810  is turned off, and if a predetermined period of time (t off ) passes, the temperature of the inside of the dry tub  20  is lowered to some degrees. If so, the control unit  220  turns on the third heater  83  again. If a predetermined period of time (t on ) passes after the third heater  83  is turned on, the temperature at the inside of the dry tub  20  is raised again. In this manner, the control unit  220  periodically turns on and off the third heater  83  to control such that the temperature at the inside of the dry tub  20  is maintained at the first dry temperature (T 1 ). In this case, the time during which the third heater  83  is turned on or turned off may be shorter than the time during which the second heater  82  is turned on or turned off in the previous embodiment of the present disclosure. 
     After operation  830 , the control unit  220  determines whether a degree of dryness of a substance contained in the dry tub  200  reaches a target degree of dryness based on a result of measurement of the dryness sensor  90  ( 840 ). 
     If a result of determination in operation  840  is that the degree of dryness measured by the dryness sensor  90  reaches the target degree of dryness, the control unit  120  determines whether a first dry time (t 1 ) passes after the first dry process starts ( 845 ). 
     If a result of determination in operation  845  is that the first dry time (t 1 ) does not pass after the first dry process (NO from  845 ), the control unit  120  maintains the temperature of the inside of the dry tub  20  at the first dry temperature (T 1 ) until the first dry time (t 1 ) passes. The reason why the first dry time (t 1 ) needs to wait to pass even after the degree of dryness of the substance reaches the target degree of dryness is to cover inaccuracy of the dryness sensor. That is, when the degree of dryness is measured using the dryness sensor, the measured value may be inaccurate. Accordingly, even if the target degree of dryness is achieved, the first dry process continues until the first dry time (t 1 ) passes. 
     If a result of determination in operation  845  is that the first dry time (t 1 ) passes after the first dry process starts, the control unit  120  allows the temperature of the inside of the dry tub  20  to be maintained at the first dry temperature (T 1 ) by repeating turning on and off the third heater  83 . 
     If a result of determination in operation  840 , the degree of dryness being measured by the dryness sensor  90  reaches the target degree of dryness, the control unit  220  starts a second dry process by raising the operation temperature of the third heater  83  ( 850 ). The reason why the control unit  220  raises the third heater  83  is to raise the temperature of the inside of the dry tub  20  from the first dry temperature (T 1 ) to the second dry temperature (T 2 ). 
     Thereafter, the control unit  220  determines whether the temperature at the inside of the dry tub  20  being measured by the temperature sensor  95  reaches the second dry temperature (T 2 ) ( 860 ). 
     If a result of determination in operation  860  is that the temperature at the inside of the dry tub  20  does not reach the second dry temperature (T 2 ), the control unit  220  keeps monitoring the temperature measured by the temperature sensor  95 . 
     If a result of determination in operation  860  is that the temperature at the inside of the dry tub  20  reaches the second dry temperature (T 2 ), the control unit  220  maintains the temperature at the inside of the dry tub  20  at the second dry temperature (T 2 ) by repeating turning on and off the third heater  83  ( 870 ). 
     After operation  870 , the control unit  120  determines whether a second dry time (t 2 ) allocated to the second dry process passes after the second dry process starts ( 880 ). 
     If a result of determination in operation  880  is that the second dry time (t 2 ) does not pass after the second dry process starts, the control unit  120  maintains the temperature at the inside of the dry tub  20  at the second dry temperature (T 2 ) by repeating turning on and off the third heater  83 . 
     If a result of determination in operation  880  is that the second dry time (t 2 ) passes after the second dry process starts, the control unit  120  controls the operation of the clothes dryer  1  such that the cooling process is performed ( 890 ). In the cooling process, the third heater  83  is turned off, and only the blower fan  61  operates. By only operating the blower fan  61 , the heat inside the dry tub  20  is discharged to the outside the clothes dryer, so that the temperature at the inside of the dry tub  20  is lowered. 
     Hereinabove, the embodiments of the present disclosure have been described. Although the descriptions have been made in relation to a case that a command to control the operation of the clothes dryer is received through the input unit  110  or  210 , the clothes dryer may further include a receiving unit (not shown). The receiving unit may receive a remote control signal being transmitted from a remote controller. The control signal transmitting/receiving between the remote controller and the receiving unit may be achieved in a wireless communication or a wired communication. In addition, the remote controller may be an additional apparatus provided to control only the operation of the clothes dryer. Alternatively, the remote controller may be an apparatus to control the operation of home appliances on the premises while being connected to the home appliances. 
     The disclosure can also be embodied as computer readable medium including computer readable codes/commands to control at least one component of the above described embodiments. The medium is any medium that can store and/or transmit the computer readable code. 
     The computer readable code may be recorded on the medium, and examples of the medium include read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks and optical data storage devices. The medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. In addition, examples of the component to be processed may include a processor or a computer process. The element to be processed may be distributed and/or included in one device. 
     Although a few embodiments of the present disclosure have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the claims and their equivalents.