Patent Publication Number: US-10760203-B2

Title: Dryer and method of controlling the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Korean Patent Application No. 10-2017-0164470, filed on Dec. 1, 2017, and 10-2018-0151380, filed on Nov. 29, 2018 in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     The present disclosure relates to a clothes dryer and a method of controlling the same. 
     2. Description of the Related Art 
     In general, a laundry treatment apparatus is an apparatus for treating laundry through various operations such as cleaning, dehydrating, and/or drying operations, and generally refers to a washing machine, a dehydrator, and a dryer. 
     The dryer is an apparatus which, while rotating a drum, blowing heated air to the inside of the drum with wet laundry loaded therein so as to dry the laundry. 
     According to how to process humid air discharged from the drum after drying of clothes, the dryer may be classified into an exhaust-type dryer and a condensing-type dryer. In addition, with a heat pump, the dryer reduces energy consumption using thermal energy discharged in an exhaust or condensing process. 
     Such a dryer dries laundry using heated air, so the dryer is configured to set a drying time according to a type of the laundry, rather than an amount of the laundry, such that the laundry is dried for a predetermined time period. 
     An operation mode is set by distinguishing laundry sensitive to heat and laundry not sensitive to heat, such that the laundry sensitive to heat is dried for a short time period in order to prevent damage to the laundry by the heat whereas the laundry not sensitive to heat is dried for a relatively long time period, thereby completely being dried. 
     In addition, Japanese Patent Application Publication No. 2007-108870 adapts a technique of changing a drying time based on temperature, rather than an amount of laundry. 
     The dryer has a drum that constantly rotates at a preset rotation speed, and, when the dryer operates for a preset time period with the same laundry, a dry state of laundry may differ according to an amount of the laundry. In addition, if temperature increases, it may increase a drying speed but this may lead to damage of the laundry, and therefore, there is a limitation in increasing the temperature. 
     In addition, if the drying time increases, the drying operation cannot be terminated at an initially set timing, thereby increasing user inconvenience. 
     U.S. Pat. No. 1,414,624 discloses accurately calculating a remaining time by sensing an amount of laundry, and displaying the remaining time in order to solve the problem that a user can misunderstand a drying time when the drying time is reset during a drying operation. 
     To this end, sensing an amount of laundry is described, but this description is mainly about displaying a remaining time, and this related art discloses just sensing the amount of laundry, not a detailed method therefor, and thus, it does not proposes a specific method of determining the amount of laundry using a measurement and enhancing accuracy of the determination. 
     In addition, Korean Patent No. 1505189 discloses sensing an amount of laundry using a current flowing in a motor. This disclosure describes a step of accelerating the motor and a step of maintaining the motor at a constant speed, for the purpose of sensing an accurate quantity of laundry, and proposes calculating an amount of laundry using current values in the accelerating step and the maintaining step. 
     However, there is a limitation in applying this related art to a dryer since the related art is a method applied to a washing machine. In addition, a method of setting an operation time according to an amount of laundry has been applied to existing washing machines. 
     However, unlike a washing machine, in a dryer, wet laundry is loaded, so there is difference in weight between dry laundry and wet laundry and a rotation speed during a drying operation of the dryer does not change a lot, and the dryer and the washing machine are driven in different ways since the washing machine aims to remove foreign substances using friction and dropping of laundry and the dryer aims to dry laundry, and therefore, there is a limitation in applying a method of the washing machine to the dryer. 
     In particular, because wet laundry is heavier than dry laundry, a considerable amount of currents is required for initial driving, and an amount of laundry may be measured differently according to an initial position of the laundry and movement of the laundry by driving of a motor. In addition, unlike the washing machine, the dryer dries clothes using heated air and rotation of drum, not in a manner of dehydrating moisture of wet laundry by a centrifugal force, so, when a drum rotates at a high speed, the laundry is dried not in a state of being stuck with the drum, and, when the drum rotates at a low speed, clothes does move enough and thus only some of the clothes are dried. 
     Wet laundry is easily stuck with a wall surface of a drum compared to dry laundry, and thus, unlike a washing machine rotating along with a drum, a dryer for towing laundry and dropping the laundry to dry the same has a problem that drying performance is significantly degraded when the laundry is stuck with a wall surface of a drum. 
     Thus, unlike the washing machine, it is necessary to consider rotation of the drum to easily tow wet laundry and drop the laundry. 
     In addition, there is a problem that a deviation in measured amounts of clothes occurs according to a method of rotating the drum of the dryer and a speed and a time of rotating the drum. 
     A different problem may happen according to connection between a motor and a drum and a method of rotating the drum, and it is necessary to solve this problem. 
     In particular, when it comes to applying a pulley-type driving method, a slip between a belt and a drum may occur. The pulley-type method is a method in which the drum in contact with the belt rotates by movement of the belt when the belt connected to the motor moves upon operation of the motor. Since a slip between the belt and the drum occurs when the motor rotates at a high speed, there is a problem that the drum does not rotate a preset number of times of rotation. 
     In addition, if laundry accommodated in the dryer increases, a driving power as great as an increase in weight of the laundry is required, but, in a method of being towed by a belt, the load increases significantly and thus a slip is more likely to occur. 
     SUMMARY OF THE DISCLOSURE 
     The present disclosure provides a dryer and a method of controlling the same, the dryer which is capable of quickly and accurately determining an amount of laundry loaded in the dryer and controlling a drying operation according to the amount of the laundry. 
     The present disclosure provides a dryer and a method of controlling the same, the dryer which rotates a drum according to an operation pattern, including an acceleration stage in which a rotation speed of the drum increases and a maintaining stage in which the rotation speed is maintained, such that laundry repeatedly moves within the drum. 
     The present disclosure provides a dryer and a method of controlling the same, the dryer which controls a rotation speed of a drum such that laundry moves to a predetermined height, without being stuck with the drum, and is then dropped. 
     In one general aspect of the present disclosure, there is provided a dryer including: a drum in which laundry is accommodated; a motor connected with the drum via a drive belt and configured to rotate the drum; a blow fan configured to circulate air, passing through the drum, in response to driving of the motor; a driving controller configured to apply operation power to the motor to operate or stop the motor, and control a rotation speed of the motor; a current sensing unit configured to measure a current value of the motor; and a controller configured to: control the driving controller such that the drum rotates according to an operation pattern, including an acceleration stage in which a rotation speed of the drum is accelerated and a maintaining stage in which the rotation speed of the drum is maintained for a predetermined time period, in order to sense an amount of laundry accommodated in the drum, and that the amount of the laundry is calculated based on current values sensed in the acceleration stage and the maintaining stage, wherein the controller is further configured to perform control to maintain the rotation speed of the drum within a range of 39 rpm to 63 rpm such that, during the maintaining stage, the laundry is lifted by the rotation of the drum and is dropped. 
     The controller may set the operation pattern by further adding, after the retention period, a stopping stage in which the rotation speed of the drum decreases. 
     In another general aspect of the present disclosure, there is provided a dryer including: a blow fan configured to circulate air, passing through the drum, in response to driving of the motor; a driving controller configured to apply operation power to the motor to operate or stop the motor, and control a rotation speed of the motor; a heat pump module configured to remove moisture from air flowing to the drum, and heat the air; a current sensing unit configured to measure a current value of the motor; and a controller configured to: control the driving controller such that a sensing step of sensing an amount of the laundry accommodated in the drum and a drying step of drying the laundry are distinguished, a rotation speed of the drum increases to a preset rotation speed in the drying step, the preset rotation speed is maintained for a predetermined time period, and then the drum stops rotating; determine the amount of the laundry based on the current value sensed by the current sensing unit while the drum rotates; and set the rotation speed of the drum according to the amount of the laundry, thereby performing a drying operation. 
     In another general aspect of the present disclosure, there is provided a dryer including: a drum in which laundry is accommodated; a motor connected with the drum via a drive belt and configured to rotate the drum; a blow fan configured to circulate air, passing through the drum, in response to driving of the motor; a driving controller configured to apply operation power to the motor to operate or stop the motor, and control a rotation speed of the motor; a current sensing unit configured to measure a current of the motor; and a controller configured to: control the driving controller such that the drum rotates according to an operation pattern in a sensing step of sensing an amount of the laundry in the drum and in a drying step of drying the laundry, the operation pattern including an acceleration stage in which a rotation speed of the drum increases and a maintaining stage in which the rotation speed of the drum is maintained for a predetermined time period; and determine the amount of the laundry based on a current value sensed by the current sensing unit while the drum rotates in the sensing step, such that the drum operates according to the amount of the laundry in the drying step so as to dry the laundry, wherein the controller is further configured to maintain the rotation speed of the drum within a range of 39 rpm to 63 rpm in the maintaining stage. 
     In yet another general aspect of the present disclosure, there is provided a method of controlling a dryer, the method including: a step of loading laundry into a drum; a step of rotating the drum by accelerating the drum to a speed at which the laundry in the drum is lifted by the drum and dropped; a step of storing a current value of the motor, which is sensed by a current sensing unit while the drum rotates; a step of sensing an amount of the laundry according to the current value; a step of setting a drying time of a drying operation and a rotation speed of the drum according to the amount of the laundry; and a step of performing the drying operation by operating the drum and a blow fan. 
     The step of performing the drying operation may further include: a step of drying the laundry in a manner in which the drum rotates at a first rotation speed when the amount of the laundry is a few loads; and a step of drying the laundry in a manner in which the drum rotates a second rotation speed higher than the first rotation speed when the amount of the laundry is medium loads or large loads. 
     The dryer and the method of controlling the same according to the present disclosure may measure a current supplied to rotate the drum and extract a force applied to laundry in the drum to measure an amount of the laundry, thereby minimizing an error in the amount of laundry and thus enhancing accuracy of the measurement and improving a drying time. 
     The present disclosure may control a rotation speed so that wet laundry is lifted by rotation of a drum, without being stuck with the drum, and then dropped. 
     The present disclosure may measure an amount of laundry while the laundry is moving in the drum. 
     The present disclosure may set an acceleration stage of increasing a rotation speed of the drum, such that the acceleration stage is longer than a retention step, thereby efficiently transferring a driving force of the motor to the drum. 
     The present disclosure may prevent a slip between a belt connecting the motor and the drum and the drum. The present disclosure may set a drying time in consideration of both a calculated amount of laundry and a type of the laundry, such that damage to the laundry is prevented and over-drying or less-drying of the laundry is solved, thereby efficiently drying the laundry. 
     The present disclosure may change a setting according to a state of laundry sensed during a drying operation, such that the laundry is completely dried within a preset drying time, improving user convenience and product reliability. 
     In addition, the present disclosure may set a drying time or a rotation speed during a drying operation according to an amount of laundry. 
     The present disclosure may change a drying time or a rotation speed according to an amount of laundry, thereby reducing the drying time and efficiently drying the laundry. 
     In addition, the present disclosure may change a setting during a drying operation according to a dryness degree, thereby reducing a drying time. 
     The present disclosure may save energy by reducing a drying time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments will be described in detail with reference to the following drawings in which like reference numerals refer to like elements wherein: 
         FIG. 1  is a perspective view of a dryer according to an embodiment of the present disclosure; 
         FIG. 2  is a perspective view illustrating the interior of the dryer of  FIG. 1 ; 
         FIG. 3  is a diagram for explanation of air circulation in the dryer of  FIG. 1 ; 
         FIG. 4  is a diagram for explanation of air circulation and refrigerant circulation in the dryer of  FIG. 1 ; 
         FIG. 5  is a diagram illustrating a structure of a dryer, in which air is recollected from a drum in a flow path and a foreign substance is collected, according to an embodiment of the present disclosure; 
         FIG. 6  is a block diagram briefly illustrating control configuration of a dryer according to an embodiment of the present disclosure; 
         FIG. 7  is a block diagram briefly illustrating control operation of a heat pump of a dryer according to the present disclosure; 
         FIG. 8  is a diagram for explanation of configuration and operation for driving a drum and a blow fan of a dryer according to an embodiment of the present disclosure; 
         FIG. 9  is a diagram illustrating an operation pattern for sensing an amount of laundry in a dryer according to an embodiment of the present disclosure; 
         FIG. 10  is a diagram for explanation of the operation pattern shown in  FIG. 9 ; 
         FIG. 11  is a diagram illustrating a current waveform sensed in accordance with the operation pattern shown in  FIG. 9 ; 
         FIG. 12  is a diagram for explanation of movement of laundry in accordance with a rotation speed of a dryer according to an embodiment of the present disclosure; 
         FIG. 13  is a diagram for explanation of movement of laundry in a drum in accordance with the operation pattern shown in  FIG. 9 ; 
         FIG. 14  is a diagram for explanation of sensed properties in accordance with the amount of laundry in a dryer according to an embodiment of the present disclosure; 
         FIGS. 15 to 17  are graphs illustrating results of sensing an amount of laundry in a dryer according to an embodiment of the present disclosure; 
         FIG. 18  is a flowchart illustrating a method of controlling a dryer according to an embodiment of the present disclosure; and 
         FIG. 19  is a diagram illustrating a control method in accordance with the amount of laundry in a dryer according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Advantages and features of the present disclosure and a method of achieving the same will be clearly understood from embodiments described below in detail with reference to the accompanying drawings. However, the present disclosure is not limited to the following embodiments and may be implemented in various different forms, and the embodiments are provided merely for complete disclosure of the present disclosure and to fully convey the scope of the disclosure to those of ordinary skill in the art to which the present disclosure pertains, and the embodiments are provided merely for complete disclosure of the present disclosure and to fully convey the scope of the disclosure to those of ordinary skill in the art to which the present disclosure pertains. A controller and any other component included in the present disclosure may be implemented by one or more micro processors and may be implemented by a hardware device. 
       FIG. 1  is a perspective view of a dryer according to an embodiment of the present disclosure.  FIG. 2  is a perspective view illustrating the interior of the dryer of  FIG. 1 , and  FIG. 3  is a diagram for explanation of air circulation in the dryer of  FIG. 1 . 
     A driver  1  of the present disclosure is configured as illustrated in  FIGS. 1, 2, and 3 . 
     The dryer  1  according to the present disclosure includes: a cabinet  10 , a drum  30  disposed in the cabinet and rotating with a laundry loaded therein; a driver  60  for rotating the drum  30 , a heat pump module  50 ,  52 ,  53 ,  54 , and  58  for heating air circulating in the drum  30  and to thereby the laundry; a blow fan  64  for circulating air in the drum  30 ; a heater  69  for heating air being introduced into the drum  30 ; and a circulation flow path  66  for guiding an airflow. 
     The cabinet  10  defines the exterior of the dryer, and provides a space in which the drum  30  and any other components are arranged. The cabinet  10  is formed in an entire rectangular shape. 
     A door  20  is disposed on the front surface of the cabinet  10 , and the door  20  is rotated to the left and to the right so as to open and close the inside of the cabinet  10 . 
     The cabinet  10  includes a front cover  11 , a top plate  16 , side covers  12  and  13 , a rear cover  15 , and a base  14 . 
     An entry hole (not shown) is formed in the front cover  11 , and the door  20  for opening and closing the entry hole. The entry hole communicates with the drum  30 . 
     The door  20  may be rotatably coupled to the front cover  11  and include a door glass  22 . The door glass  22  is formed of a transparent member so as to allow a user to see the inside of the drum  30 , and has a shape convex toward the inside of the drum  20 . 
     A control panel  17  may be disposed above the front cover  11 . The control panel  17  includes: a display (e.g., an LCD, an LED panel, etc.) for displaying information about the state of operation of the dryer; an manipulation unit (e.g., a button, a dial, a touch screen, etc.) for receiving a command from a user to operate the dryer; and a speaker (not shown) for outputting a voice guidance about the state of operation, an effect sound, or an alert sound. 
     The drum  30  is disposed in the inside of the cabinet  10 , and the blow fan  64  and the heat pump module are disposed under the drum  30  in order to maximize the capacity of the drum  30 . 
     The drum  30  is formed in a cylindrical shape, and the front surface and the rear surface thereof are opened, wherein the front surface communicates with the entry hole. In addition, an air inlet (not shown) is formed on the rear surface of the drum  30  so that air is introduced, and the air inlet is connected to the circulation flow path for circulating air. 
     A lifter  31  is installed in the inside of the drum  30 , and the lifter  31  lifts up laundry within the drum while rotating and then lets the laundry freely fall. The drum is supported by a supporter (not shown) provided in the cabinet. 
     The driver  60  includes a motor fixed to a base  14  of the cabinet  10 . The motor provides power for rotating the drum, and is also connected to the blow fan  64 , thereby rotating the blow fan. The motor is a motor having double shafts to which the drum  30  and the blow fan  64  are connected, respectively. 
     The motor includes a drive pulley, which is engaged with a drive belt  164  wound around the drum  30 , on the shaft connected to the drum. The drum  30  may rotate forward or backward by the rotation of the motor. An idle pulley (not shown) may be installed to adjust tension of the drive belt. The drive belt may surround the circumferential surface of the drum, while engaged with the drive pulley and the idle pulley. When the motor rotates, the drive belt is transferred by the drive pulley and the drum  30  rotates by a friction force applied between the drum and the drive belt. 
     The blow fan  64  may rotates by the motor of the driver  60 . By the rotation of the blow fan  64 , air in the drum  30  is introduced into a suction duct  68 . The suction duct  68  may be included in the circulation flow path  66 . 
     When the blow fan  64  rotates, air discharged from the drum  30  is guided to the suction duct  68  and the supplied to the blow fan  64 . The suction duct  68  is coupled to the front surface of a front supporter, and communicates with an air inlet of the blow fan  64 . The blow fan  64  circulates air in a manner in which air suctioned from the drum passes through the heat pump module through the circulation flow path  66  and then flows back to the drum. 
     When the drum  30  rotates forward, air flows from the back of the drum to the inside of the drum and air is discharged to the front of the drum. In addition, when the drum rotates backward, air may flows from the front of the drum and discharged to the back of the drum. 
     The circulation flow path  66  may be configured in various ways according to an embodiment. The circulation flow path  66  guides air, discharged from the blow fan, to the heat pump module and also guides air, discharged from the heat pump module, to the drum through the heater. The circulation flow path  66  may be provided even at the back of the drum so that heated air flows into the drum  30 . 
     The circulation flow path along which air within the drum circulates may be formed in various ways. The circulation flow path  66  may be connected to the drum, thereby forming a closed loop for air circulation. In addition, the circulation flow path may be connected to a discharge duct (not shown) through which air is discharged, and a suction duct (not shown) through which outdoor air is introduced. 
     A filter assembly  19  is installed at the entry hole to collect lint included in air, which is discharged from the drum  30  and then flows to the suction duct. 
     The heat pump module circulates a refrigerant, driving the refrigerant in a heat pump cycle. 
     Laundry loaded in the drum may be dried by heated air supplied to the drum. Air discharged from the drum flows into the circulation flow path with containing moisture evaporated from the laundry during a drying operation, and the discharged air is heated through the heat pump module and then supplied back to the drum. 
     The heat pump module includes a compressor  50 , a condenser  52 , an evaporator  53 , and an expansion valve. 
     The heat pump module is configured such that the compressor  50 , the condenser  52 , and the evaporator  53  are connected to each other via a refrigerant pipe and thus air heated through heat exchange between a refrigerant and air in the condenser and the evaporator is supplied to the drum through circulation of the refrigerant. In some cases, the heat pump module may enable heat exchange with a medium other than the refrigerant. 
     By causing heat exchange between air flowing through the blow fan  64  from the drum  30  and a refrigerant, the evaporator  53  may recollect energy of discharged air. In addition, the evaporator  53  condenses moisture contained in the introduced air. 
     The condenser  52  causes heat exchange between air passing through the evaporator  53  and a refrigerant and discharges heated air to the drum. Air of low temperature and low humidity passing through the evaporator is introduced to the condenser and thermally exchanged with a refrigerant, and then supplied to the drum in a state of high temperature and low humidity. 
     The refrigerant discharged from the condenser passes through the evaporator and is then recollected in the compressor, the compressor  50  compresses an evaporated refrigerant and discharges the compressed refrigerant to the condenser, and the expansion valve expands the refrigerant condensed in the condenser  52 . 
     The compressor  52  and the evaporator  53  are heat exchangers. 
     Since hot and humid air discharged from the drum  30  is hotter than a refrigerant of the evaporator  53 , the air is thermally exchanged with the refrigerant while passing through the evaporator, thereby being condensed and cooled down. Accordingly, the hot and humid air is dehumidified and cooled down by the evaporator. Condensate generated in the course of condensing the air may be collected in a condensate housing (not shown) and drained. 
     In addition, the heat pump module may further include an auxiliary heat exchanger  54  and a cooling fan  58 . The auxiliary heat exchanger  54  may be configured by a detachable condensing module, which is detachable from the condenser  52 . The auxiliary heat exchanger and the cooling fan may be configured as one module or may be detachable from each other. 
     The auxiliary heat exchanger  54  may be installed in a refrigerant pipe extending from the condenser to the expansion valve with reference to a refrigerant flow direction, and cool down a refrigerant discharged from the condenser. 
     The cooling fan transfers external or internal air of the cabinet to the auxiliary heat exchanger, thereby cooling down the auxiliary heat exchanger. 
       FIG. 4  is a diagram for explanation of air circulation and refrigerant circulation in the dryer of  FIG. 1 . As illustrated in  FIG. 4 , air supplied to the drum  30  heats up laundry, absorbs moisture evaporated from the laundry, and then discharges the moisture. 
     The air is circulated by the blow fan  64 . 
     The air flows to the evaporator  53  through the drum by the blow fan, is condensed in the evaporator, and then flows to the condenser  52  in a state of low temperature and low humidity. The air  52  is heated up as a result of heat exchange with a refrigerant of the condenser  52 , and then flows back to the drum  30 . The air may be additionally heated up by a heater installed on the circulation flow path. 
     One of the heat pump module and the heater  69  may selectively operate, or the both may operate at the same time. 
     Air flows in a sequence of the drum  30 , the evaporator  53 , and the condenser  52 . 
     The refrigerant is discharged by the compressor  50  to the condenser  52  in a state of high temperature and high pressure, thermally exchanged with air in the condenser, and then flows to the evaporator  53 , thereby being evaporated. The expansion valve  59  is installed between the condenser and the evaporator. The expansion valve expands a condensed refrigerant of low temperature and high pressure and transfers the expanded refrigerant to the evaporator. The expanded refrigerant is evaporated in the evaporator  53 , flows to the compressor  50  in a state of low temperature and low pressure, and is then discharged to the condenser in a state of high temperature and high pressure. 
       FIG. 5  is a diagram illustrating a structure of a dryer, in which air is recollected from a drum in a flow path and a foreign substance is collected, according to an embodiment of the present disclosure. 
     As illustrated in  FIG. 5 , a filter assembly  19  is installed in the entry hole toward the drum, especially the front part of the drum where the front panel and the drum are connected. Air discharged from the drum passes through the filter assembly  19 , and flows to the evaporator along the circulation flow path through the blow fan. 
     In the course of flowing to the evaporator  53  from the drum  30  by the blow fan  64 , air passing through the drum may be separated from laundry while passing through the filter assembly  19  of the drum, thereby removing lint contained in the air. 
     The filter assembly  19  may include a filter case  182  fixed to the front supporter, and a lint filter  183  detachable from the filter case  182 . The filter case  182  forms an accommodation space in which a lint filter  183  is accommodated, and a filter inserting hole is formed in a top surface of the accommodation space so that the lint filter  183  is insertable into the accommodation space. The lint filter  183  may be inserted into the accommodation space through the filter inserting hole or may be drawn from the accommodation space. 
     The front surface of the drum includes an electrode  18  of a laundry sensing unit serving to sense a state of laundry in the drum. The laundry sensing unit is composed of two electrode sensors. The two electrode sensors are installed with a predetermined space apart from each other, include a cathode and an anode, and are exposed toward the drum. 
     As an electrode sensor contacts laundry while the laundry is moving by rotation of the drum, the electrode sensor senses a state of the laundry, especially, an amount of moisture contained in the laundry. A controller (not shown) determines a dry state of the laundry according to the amount of moisture contained in the laundry, sensed by the electrode sensor. 
     When the laundry is in contact with the electrode sensor, a closed circuit is formed as two polarities are conducted by the moisture contained in the laundry, and a dryness degree of clothes may be determined based on the current value as a value of a current flowing in the circuit is varied. The laundry acts as a resistance for the electrode, and a resistance value is varied according to an amount of moisture contained in the laundry, and thus, the current flowing in the circuit is varied as well. 
     The controller not just obtains the dryness degree, but also controls various electronic components of the dryer  1 . The controller may include a Central Processing Unit (CPU), and a memory for storing data in a format readable by the CPU. The controller may be one processor or a plurality of processors. 
       FIG. 6  is a block diagram briefly illustrating control configuration of a dryer according to an embodiment of the present disclosure. As illustrated in  FIG. 6 , the dryer  1  is configured as described above, and, in order to control operations, the dryer  1  includes an operator  170 , an output unit  175 , a communication unit  190 , a driver  160 , a power unit  150 , a heat pump module  120 , a pump  185 , a heater  69 , a sensor unit  130 , a memory  140 , and a controller  110  for controlling overall operations of the dryer. 
     The operator  170  includes an input means such as at least one button, switch, or touch pad installed on the control panel  17 . The operator  170  inputs an operation settings which includes a power input, an operation mode, and a laundry type setting. When a type of laundry is selected and a power key is input, the operator  170  may input data on the operation setting to the controller. 
     The output unit  175  includes: a display for displaying information on the operation setting input by the operator  170  and for outputting an operation state of the dryer; and a speaker or a buzzer for outputting voice guidance, specific sound effect, or warning sound. The display may include a menu screen for operation settings and operation control of the dryer, and output a guidance message or an alarm including at least one or a combination of a text, a numeric value, and an image with respect to the operation setting or the operation state. 
     The memory  140  may store control data for operation control of the dryer, input operation setting data, data on an operation mode, and reference data used to determine an error of the dryer. In addition, the memory  140  stores data sensed or measured during operation of the dryer, and data transmitted and received through the communication unit. The memory  140  may be a hardware storage device, such as a ROM, a RAM, an EPROM, a flash drive, and a hard drive. 
     The communication unit  190  transmits and received data in a wired or wireless manner. The communication unit  190  may be connected to a network formed in a building or at a predetermined distance, such as a home network, to transmit and receive data, may be connected to an external server, such as the Internet, and may communicate with a terminal having a control function. The communication unit  190  transmits an operation state or a drying operation progress state of the dryer, and receives a command in regard of the dryer. The communication unit  190  includes not just a short range communication module, such as Zigbee and Bluetooth, but also a communication module, such as Wi-Fi and Wibro, to transmit and receive data. 
     The power unit  150  supplies operation power by converting supplied normal power. The power unit blocks excessive currents and rectifies and smooths supplied power, thereby supplying operation power of a predetermined size. 
     The sensor unit  130  includes a plurality of sensors, measure a voltage or current of the dryer, senses a rotation speed of the motor, temperature, and humidity, and inputs measurements to the controller  110 . 
     The sensor unit  130  includes a door sensing unit  131 , a laundry sensing unit  132 , a temperature sensing unit  133 , a humidity sensing unit  134 , and a current sensing unit  135 . The sensor unit  130  may further include a pressure sensor for sensing pressure of a refrigerant of the heat pump module  120 , a temperature sensor, and a speed sensing unit for sensing a rotation speed of the motor of the driver or a rotation speed of the drum. 
     The temperature sensing unit  133  may sense internal temperature of the drum, temperature of the refrigerant or the heat exchanger in the heat pump module  120 , temperature of the heater  69 , and internal temperature of the control circuit. In addition, the temperature sensing unit includes a plurality of sensors respectively installed at different positions to sense temperature. 
     The humidity sensing unit  134  senses internal humidity of the drum and humidity of circulating air. 
     The laundry sensing unit  132  may contact laundry accommodated in the drum to sense an amount of moisture contained in the laundry. The laundry sensing unit may be included in the humidity sensing unit and may be installed separately from the humidity sensing unit. 
     The current sensing unit  135  may sense a current applied to the motor of the driver  160  and input the sensed current value to the controller  110 . 
     The door sensing unit  131  may sense whether the door  20  is opened or closed. Before performing an operation in accordance with a setting, the door sensing unit  131  senses an opened/closed state of the door and inputs a sensing signal to the controller. In addition, the door sensing unit  131  senses whether laundry is jammed 
     The heater  69  heats up air being supplied to the drum, so that the air reaches to a predetermined temperature. 
     A heater driver (not shown) supplies operation power to the heater  69  so as to operate the heater or stop operation of the heater, and controls heating temperature of the heater. The heater driver may control the heater in different manners with respect to the case where the heater  69  operates alone and the case where the heater  69  operates along with the heat pump module  120  at the same time. 
     The pump  185  operates by a pump driver (not shown) and discharges condensate to the outside. The pump  185  discharges condensate accommodated in the condensate housing, the condensate which is generated through condensation of moisture, recollected by the drum from air, in the evaporator. 
     The driver  160  controls driving of the motor to rotate the motor. The motor is connected to the drum  30  and provides power to the drum to rotate the drum. In addition, the motor is connected to the blow fan  64 , rotating the blow fan. 
     As the drum and the blow fan are connected to a single motor, the driver  160  controls the drum and the blow fan at the same time by controlling the motor. As the drum is connected to the motor through the drive belt and the pulley, the number of times of rotation of the motor per rotation of the drum has a predetermined ratio. A rotation speed of the motor is different from a rotation speed of the drum. For example, the drive pulley may be installed to allow the motor to rotate 40 to 60 times while the drum rotates once. The blow fan may rotate at a speed identical to the rotation speed of the motor according to a structure of connection with a driving shaft of the motor. 
     The blow fan  64  controls a flow of air in the dryer. The blow fan  64  supplies heated air to the drum  30 , suctions moisture-contained air from the drum, and causes the moisture-contained air to flow to the heat pump module  120 . 
     The heat pump module  120  includes the compressor  50  and a heat exchanger, thereby removing moisture from circulating air through heat exchange with a refrigerant and heating up the air. 
     The controller  110  performs control to store an operation setting, received from the operation unit  170 , in the memory  140 , process data transmitted and received through the communication unit  190 , and output the operation setting and an operation state of the dryer through the output unit  175 . When an application for controlling the dryer is installed and there is a terminal (not shown) wirelessly connected with the dryer, the controller may control the communication unit to transmit data of the dryer to the terminal. 
     The controller  110  controls operation of the drum and the blow fan by means of the driver  160  according to the operation setting received from the operation unit  170 , and variably controls operation according to a sensing value of the sensor unit  130 . The controller  110  controls the heat pump module  120  during operation to heat up air, and controls either or both of the heater and the heat pump module to operate so as to control temperature of air supplied to the drum. 
     The controller  110  controls a series of procedures for drying laundry loaded into the drum. 
     The controller  110  senses an amount (quantity) of laundry loaded into the drum, and sets a drying time according to the amount of the laundry. Upon operation of the motor, the controller  110  stores and analyzes a current value sensed by the current sensing unit  280  to determine a state of the motor and determine the amount of the laundry accommodated in the drum. 
     In the case of sensing an amount (quantity) of the laundry, if the motor rotates by the driver  160 , the controller  110  applies a control command so as to increase a rotation speed of the motor to a preset rotation speed, maintain the preset rotation speed for a predetermined time period, and then stop the rotation. The controller  110  determines an amount of the laundry by analyzing current values sensed by the current sensing unit  135  in an acceleration stage in which the motor reaches the preset rotation speed, and a maintaining stage in which the preset rotation speed is maintained. 
     In addition, when sensing an amount (quantity) of the laundry, the controller  110  may control the driver  160  such that the drum repeatedly performs an operation of rotating in one direction, rotating in the opposite direction, and rotating in one direction again. 
     While the amount (quantity) of the laundry is being sensed, the controller  110  controls the heat pump module  120  to stop operating, and, when the amount of the laundry is sensed, the controller  110  may control the heat pump module to operate according to a setting. 
     The controller  110  sets a rotation speed of the motor so that the drum rotates at a predetermined rotation speed. The controller sets a rotation speed of the drum so that laundry in the drum is dropped while moving along with the drum by the rotation of the drum. When the drum rotates by the motor, the blow fan  64  rotates along with the rotation of the drum  30 , thereby causing air to flow through the circulation flow path. 
     During a drying operation, the controller  110  may determine whether laundry is properly dried, based on data sensed and received by a plurality of sensors in the sensor unit  130 . According to a dry state of laundry sensed by the laundry sensing unit, the controller  110  changes a drying time or a rotation speed of the drum. In addition, when an error occurs during the drying operation, the controller  110  may perform control to output the error through the output unit  240  and stop operation of the dryer according to the occurred error. 
       FIG. 7  is a block diagram briefly illustrating control operation of a heat pump of a dryer according to the present disclosure. 
     As illustrated in  FIG. 7 , the heat pump module  120  may further include a heat pump controller  121 , a heat pump driver  122 , a compressor  50 , a valve  59 , a cooling fan  58 , a pressure sensor  128 , a temperature sensor  129 , a condenser  52 , and an evaporator  53 . In addition, the heat pump module  120  further include an auxiliary heat exchanger. 
     The heat pump controller  121  controls the compressor  50  to operate in accordance with a control command from the controller  110 . The heat pump controller  121  sets an operation frequency of the compressor, variably controls the compressor in accordance with data sensed by the pressure sensor  128  and the temperature sensor  129 , and controls a rotation speed of the cooling fan  58 . 
     The heat pump driver  122  controls driving of the compressor  50 , the valve  59 , and the cooling fan  58 . The heat pump driver  122  may be classified into a compressor driver, a valve driver, and a fan driver which are provided separately. 
     The heat pump driver  122  supplies operation power so that the compressor  50  operates according to a setting by the heat pump controller  121 . The heat pump driver  122  may include an inverter (not shown). The heat pump driver  122  control opening and closing of the valve  59  which controls a flow of a refrigerant. For example, the heat pump driver  122  controls a four-way valve to change a flow path of a refrigerant, and controls opening and closing of the valve  59  with respect to a refrigerant discharged from the condenser such that the refrigerant expands and is evaporated in the evaporator  53 . 
     The heat pump driver  122  supplies operation power to a fan motor so that the cooling fan  58  is rotated. The cooling fan  58  is rotated at a predetermined rotation speed upon driving of the fan motor. The cooling fan  58  may be provided in an auxiliary heat exchanger  54 . The auxiliary heat exchanger  54  is configured by a separate condensing module separable from the condenser  52 , and installed in a refrigerant pipe connected from the condenser to the expansion valve with reference to a refrigerant flow direction to cool down a refrigerant discharged from the condenser. The cooling fan  58  transfers external or internal air of the cabinet to the auxiliary heat exchanger, thereby cooling down the auxiliary heat exchanger. 
     Refrigerants in the condenser  52  and the evaporator  53  thermally exchange with air circulating in the drum. Additional fans are not installed in the condenser and the evaporator, and heat is exchanged with air circulated by the blow fan  64 . 
     The refrigerant flows in a sequence of the compressor  50 , the condenser  52 , and the evaporator  53 , and the air circulates in a sequence of the drum, the evaporator, and the condenser. The air may pass through the heater  69  before being supplied from the condenser to the drum. 
     The compressor  50  discharges a refrigerant of high temperature and high pressure, and the condenser  52  condenses the refrigerant and discharges the condensed refrigerant. Here, since heat is generated in the course of condensing the refrigerant by the condenser, air passing through the condenser is heated up by the heat generated by the condenser. 
     The refrigerant discharged from the condenser is evaporated in the evaporator by the expansion valve. Since an endergonic reaction, in which surrounding heat is absorbed during vaporization of a refrigerant, occurs in the evaporator, air passing through the evaporator is cooled down and moisture contained in the air is condensed, thereby generating condensate. 
     As the moisture cooled down in the evaporator  53  is generated as condensate, the air is dehumidified and then supplied to the condenser. Air passing through the condenser is heated up and then supplied to the drum. 
       FIG. 8  is a diagram for explanation of configuration and operation for driving a drum and a blow fan of a dryer according to an embodiment of the present disclosure. 
     As illustrated in (a) of  FIG. 8 , the driver  160  includes a driving controller  161  and a motor  162 . The driving controller  161  applies operation power to the motor  162  such that the motor rotates at a preset rotation speed. 
     In accordance with a control command from the controller  110 , the driving controller  161  controls the motor to operate or stop operating, and also controls a rotation speed of the motor such that the motor operates at a preset rotation speed. 
     In accordance with a control command, the driving controller  161  controls a rotation direction, a rotation angle, and a rotation speed of the motor  162 . In response to operation of the motor  162 , the drum  30  and the blow fan  64  operate. 
     As illustrated in (b) of  FIG. 8 , with the drive belt  164  is wound around the drum  30 , and, as the drive belt  164  moves by rotation of the motor  162 , the drum rotates along with the drive belt by a friction force between the drive belt and the drum. 
     As the blow fan  64  is connected to the other shaft of the motor  162 , the blow fan rotates along with the drum upon rotation of the motor. 
     When the motor rotates forward, the drum rotates forward as well. When the motor rotates forward, air flows from the back of the drum to the inside of the drum by the blow fan, and air is suctioned into a circulation flow path, provided on the front surface of the drum, passes through the evaporator and the condenser, and then flows to the drum again, thereby circulating. 
     Meanwhile, when the motor  162  rotates backward, the drum  30  and the blow fan  64  rotates backward as well. Due to the backward rotation of the blow fan, air is supplied to the front surface of the drum, flows to the rear surface of the drum, and then passes through the condenser and the evaporator. When the blow fan rotates backward, the air passing through the evaporator is supplied to the drum, and therefore, unheated air flows to the drum. 
     The driving controller  161  may control the motor to rotate forward during a drying operation so as to rotate the drum and the blow fan forward, while controlling the motor to rotate backward a predetermined number of times during the drying operation so as to prevent entanglement of laundry. 
     In the case where the motor rotates by suddenly accelerating a rotation speed thereof as the drum  30  rotates by the drive belt  164 , a slip between the drum and the drive belt may occur. 
     That is, even when the motor is rotating, a slip between the drive belt and the drum may occur and thus the drum is not capable of rotating in correspondence with the rotation speed of the motor. 
     Accordingly, the driving controller  161  controls the motor  162  such that a target speed is reached by accelerating for a predetermined time period, rather than immediately accelerating up to the target speed from the beginning. A degree of acceleration in the rotation speed of the motor in an acceleration stage is described as an acceleration gradient. 
     Due to the characteristic that a driving force of the motor is transferred to the drum by the belt, the controller  110  sets a degree of acceleration of the motor to reach a target rotation speed, thereby causing the drum to rotate without a slip. 
       FIG. 9  is a diagram illustrating an operation pattern for sensing an amount of laundry in a dryer according to an embodiment of the present disclosure, and  FIG. 10  is a diagram for explanation of the operation pattern shown in  FIG. 9 . 
     As illustrated in (a) of  FIG. 9 , the controller  110  controls a rotation speed of the motor in order to determine an amount of laundry. 
     The controller  110  divides an operation of the dryer into a sensing step of sensing the amount of laundry, and a drying step of performing a drying operation to dry the laundry. 
     In the sensing step, the controller  110  repeatedly performs an operation pattern to sense an amount of laundry. 
     The controller  110  may control the driver  60  such that the drum repeatedly performs an operation of stopping after rotation in any one direction and rotating in the opposite direction after a predetermined time period. During the rotation of the drum, the controller  110  stores a current value for each stage, measured by the current sensing unit  135 , and determine the amount of laundry. 
     Hereinafter, based on an operation pattern which indicates that the drum  30  rotates in any one direction for a preset time period, an operation of the drum in an effort to sense the amount of laundry will be described. 
     The controller  110  senses an amount of laundry for an 11 th  time period T 11 . The sensing step may be set to the 11 th  time period. When the amount of laundry is sensed, the controller  110  controls the driver to perform a drying operation in the drying step. The drying step may be set to a 12 th  time period, and correspond to a time period which lasts until operation of the dryer is terminated. 
     During the 11 th  time period T 11 , the controller  110  senses the amount of laundry five to six times. 
     The controller  110  controls the driver to repeatedly perform the operation pattern during the 11 th  time period with changing a rotation direction. 
     The controller  110  performs control to perform the operation pattern just once for a 13 th  time period T 13  and sense the amount of laundry just once for the 13 th  time period. In the operation pattern for the 13 th  time period T 13 , the drum rotates five to six times. Regardless of directions of forward rotation and backward rotation, the operation time and the sensing time are applied identically. 
     The operation pattern includes an acceleration stage in which a speed is accelerated to a target rotation speed, a maintaining stage in which the rotation speed is maintained, and a stopping stage in which the rotation is stopped. 
     In the operation pattern being performed while an amount of laundry is sensed, a rotation speed R 1  may be a target rotation speed which corresponds to a degree of speed at which the laundry is lifted by rotation of the drum and dropped. For example, in the case of sensing an amount of laundry is measured, the rotation speed R 1  of the drum may be set to 39 rpm to 63 rpm. A rotation speed of the motor corresponding to the rotation speed of the drum may be set to 2000 rpm to 3200 rpm but may vary depending on a pulley ratio. 
     In addition, as illustrated in (b) of  FIG. 9 , the controller  110  may control the driver  60  such that the drum  30  repeatedly performs an operation of rotating in any one direction, stopping rotating, and then immediately rotating in the opposite direction. 
     In this case, as described above, a time period required to perform the operation pattern once is identical to the 13 th  time period, yet, since the drum immediately rotates, a time period required to sense an amount of laundry may be a 14 th  time period T 11 ′ shorter than the 11 th  time period T 11 . 
     The controller  110  may control the driver  160  such that an amount of laundry is sensed through backward rotation, forward rotation, backward rotation, forward rotation, and then backward rotation of the drum  30 , and an drying operation T 12  is performed while the drum is kept rotating forward. The controller  110  may perform control to perform a preset drying operation after sensing the amount of laundry. In this case, rotation of the drum in a clockwise direction is defined as forward rotation, and rotation of the drum in a counter-clockwise direction is defined as backward rotation. 
     In addition, in the case of sensing an amount of laundry, if the first rotation direction is a forward direction, the controller  110  may sense the amount of laundry six times. For example, the drum  30  may rotates forward, backward, forward, backward, forward, and backward, and then perform a drying operation while rotating forward. In addition, an example is also possible in which the drum  30  senses an amount of laundry five times by starting with forward rotation, temporarily stops rotating, and then performs a drying operation while rotating forward. 
     The controller  110  senses an amount of laundry five to sixth time by repeatedly rotating backward and forward for the 11th time period T 11  or for the 14 th  time period T 11 ′. In some cases, when the amount of laundry is sensed, a drying operation may be performed after the drum rotates five times in any one direction consecutively, or an operation in which the drum rotates two times in any one direction, rotates in the opposite direction, and rotates in the any one direction again may be performed repeatedly. When the amount of laundry is sensed, any of various rotation directions of the drum may be set, but the controller  110  controls the driver such that the drum  30  operates in accordance with the operation pattern including the acceleration stage, the maintaining stage, and the stopping stage. 
     In the case where the drum  30  rotates forward, as heated air is supplied to the drum, the drum rotates forward in the drying operation. During the drying operation, the drum may rotate backward a predetermined number of times in order to prevent entanglement of laundry. 
     As illustrated in  FIG. 10 , when sensing the amount of the laundry, the controller  110  applies a control command to the driver  160  such that the drum rotates in accordance with the operation pattern. 
     When sensing the amount of the laundry, the controller  110  may divides the operation pattern into an acceleration stage D 1  in which a rotation speed increases to a target rotation speed R 1 , and a maintaining stage D 2  in which the target rotation speed is maintained. In addition, the controller  110  may perform control by further adding a stopping stage D 3  which comes after the maintaining stage, and in which the rotation speed of the drum is decelerated to stop. 
     The controller  110  may set the acceleration stage D 1  and the maintaining stage D 2  such that a length of the acceleration stage D 1  is longer than a length of the maintaining stage. In addition, the controller  110  may set a length of the stopping stage D 3  to be shorter than the length of the maintaining stage D 2 . In this case, a length of each stage refers to a time period, and the fact that the length of the acceleration stage is longer than the length of the maintaining stage means that a time period in which the rotation speed of the drum is accelerated is longer than a time period in which the rotation speed is maintained. 
     For example, the length of the acceleration stage D 1  and the length of the maintaining stage D 2  may be set to a ratio of 5:3. 
     In addition, when the stopping stage D 3  is included, the length of the acceleration stage D 1 , the length of the maintaining stage D 2 , and the length of the stopping stage may be set to a ratio of 5:3:2. 
     For example, when the 13 th  time period required to perform the operation pattern once is assumed to be 10 seconds, the acceleration stage, the maintaining stage, and the stopping stage may be set to 5 seconds, 3 seconds, and 2 seconds, respectively. 
     The ratio regarding the lengths of the stages may be varied, but, since a slip can occur by the belt of the drive pulley which connects the motor and the drum, it is preferable to make setting so as to prevent occurrence of the slip. 
     In the case where a driving torque of the motor is constant, if a speed increases, a friction torque decreases, possibly causing the slip to occur. Thus, an acceleration speed may be set within a range in which the slip does not occur. 
     A rotation speed of the drum should not be accelerated unexpectedly in order to prevent the slip, and thus, the acceleration stage may be set such that the rotation speed increases at a preset acceleration gradient. Accordingly, the acceleration stage is preferably set to be longer than the maintaining stage. The acceleration gradient refers to a variation of acceleration. 
     A time period in which the target rotation speed is reached in the acceleration stage may be varied according to the acceleration gradient, but the controller  110  may determine an amount of laundry by calculating a current values for each stage with reference to a designated time period. 
     When the drum  30  is performing the operation pattern of accelerating, retaining, and stopping for the 13 th  time period, the drum rotates five to six times. In one operation pattern, the controller senses an amount of laundry using a current value sensed by the current sensing unit  135 . The controller may and senses an amount of laundry using a sensed current value for each of the acceleration stage, the maintaining stage, and the stopping stage which are set at time intervals identically set regardless of a rotation direction of the drum. 
     When sensing the amount of laundry, the controller  110  discriminates current values, sensed by the current sensing unit  135 , for the acceleration stage D 1 , the maintaining stage D 2 , or the stopping stage D 3  according to a preset ratio. The controller  110  performs control such that the drum repeatedly performs the operation pattern a preset number of time with changing a rotation direction of the drum to a forward direction and a backward direction. 
     During one round of the operation pattern in which the drum rotates in three stages including the acceleration stage, the maintaining stage, and the stopping stage, the controller  110  discriminates current lq 1  and lq 2 , measured by the current sensing unit  135 , for the respective stages, and stores and accumulates the discriminated currents lq 1  and lq 2  according to the respective stages. The controller  110  determines an amount of laundry by calculating an average of current values in the acceleration stage D 1  and an average of current values in the maintaining stage D 2 . 
     The controller  110  repeatedly performs the operation pattern five to six times, and senses the amount of laundry for the 11 th  time period T 11  or for the 14 th  time period T 11 ′ with the stopping stage added. For example, if the 13 th  time period T 13  for performing the operation pattern once is 10 seconds and the operation pattern is performed five times, a time period for sensing an amount of laundry may be set to about 50 to 60 seconds. 
     The controller  110  calculates an average of current values for each stage, sensed during each round of the operation pattern, and determines the amount of laundry based on a value obtained by subtracting a current value of the maintaining stage from a current value of the acceleration stage. The controller  110  calculates the amount of laundry into a value obtained by subtracting a half the average current value of the maintaining stage from the average current value of the acceleration stage. 
     In order to reduce an error caused by a type of laundry and a friction force between the drum and the drive belt, the controller  110  subtracts a half the (average) current value of the maintaining stage. 
     An average of current values aggregated in the acceleration stage is an average of currents that are consumed to reach to a target rotation speed from a stopped state, and 50% of the influence of current components by friction is applied. In addition, as for an average of currents in the maintaining stage, 100% of the friction coefficient of the drive belt  164  and the drum  30  are applied, and thus, 100% of the influence of the friction is applied. 
     Accordingly, in order to eliminate the influence of the friction of the drive belt  164 , the controller  110  subtracts an average of current values in the maintaining stage from an average of current values in the acceleration stage, and, since 50% of the influence of the friction in the acceleration stage is applied and 100% of the influence of the friction in the maintaining stage is applied, the controller  110  may determine an amount of laundry into a value obtained by subtracting a half the average of current values in the maintaining stage from the average of current values in the acceleration stage. 
       FIG. 11  is a diagram illustrating a current waveform sensed in accordance with the operation pattern shown in  FIG. 9 . 
     As illustrated (a) and (b) of  FIG. 11 , a different current value is measured by the motor according to the amount of laundry. 
     When the amount of laundry is small, a current value is measured low, except for an initial driving current, As illustrated (a) of  FIG. 11 . And when there is a great amount of laundry, a current value is measured higher than in (a) of  FIG. 11 , as illustrated (b) of  FIG. 11 . 
     Accordingly, an amount of laundry may be determined based on a current value used to rotate the drum with laundry loaded therein. 
     The current sensing unit  135  may measure currents according to an initial driving stage A, an acceleration stage B, and a maintaining stage C. In the initial driving stage, there is a big error due to a position of laundry or positional alignment of the motor in the initial driving, and a big error in current values at an initial driving time, and thus, a current value of the initial driving stage A may be excluded. When necessary, the initial driving stage may be included in the acceleration stage. 
     The controller  110  controls the driver to accelerate such that the rotation speed of the drum  30  increases to reach a target rotation speed. While the drum  30  is rotating, laundry in the drum  30  is initially in a (tumble) state in which the laundry is rotating and rolling in the drum, and, as the rotation speed of the drum  30  increases, an amount of movement of the laundry increases due to a centrifugal force in the drum. When the rotation speed of the drum  30  reaches the target rotation speed, the laundry is in a state in which the laundry is lifted by the rotation of the drum and dropped. 
     The controller  110  performs control to accelerates the rotation speed of the motor to a degree in which the laundry is lifted by the rotation of the drum and then dropped, and then to maintain the rotation speed. 
     When the drum rotates upon operation of the dryer, a variety of forces is applied to the drum with laundry loaded therein. When the drum rotates, a motor torque, an inertia torque, a friction torque, and a load torque are applied to the drum. 
     The motor torque is a force applied to rotate the motor connected to the drum; the initial torque is a force caused by inertia to maintain the existing movement state (rotation) when a speed is accelerated or decelerated during the rotation; the friction torque is a force resisting rotation by friction between the drum and the laundry, between the door and the laundry, between in the laundry, and between the drive belt and the drum; and the load torque is a force resisting rotation by a weight of the laundry. 
     While the drum is rotating, a force applied to the laundry at an angle of em is as follows. This is a force applied when the drum is moved by the angle of em from a stopped state. 
     The motor torque is a force required to operate the motor, and represented as a sum of the inertia torque, the friction torque, and the load torque. The motor torque is a value obtained by multiplying a force of lifting the laundry by a radius of the drum. The inertia torque is a force resisting rotation by inertia of the drum or inertia according to a distribution of laundry when a rotation speed is accelerated or decelerated during the rotation. In this case, the inertia torque is proportional to a weight of the laundry and a square of the radius of the drum. The friction torque is a friction force applied between laundry and a tub, between laundry and a door, and between a drive belt and a drum, and therefore, the friction torque is proportional to a rotation speed. The friction torque may be calculated into a value of multiplication between a friction coefficient and the rotation speed. The load torque is a force of gravity applied according to a distribution of the laundry, and may be calculated based on a weight of the laundry, acceleration due to gravity, the radius of the drum, and an angle. 
     The force of gravity influences a force applied to the laundry at a specific angle θm, but, since the drum is rotating, the applied force may be calculated into a value obtained by multiplying gravity by sin θm. The force of gravity is determined by acceleration due to gravity, the radius of the drum, and the weight of the drum. 
     While the drum is rotating, the motor torque, the inertia torque, the friction torque, and the load torque are applied at the same time and these force components are reflected in a current value of the motor, and therefore, the controller  110  calculates an amount of laundry using current values sensed by the current sensing unit  135  during operation of the motor. 
     The motor torque is considerably influenced by gravity due to a weight, and, if the weight is equal to or greater than a predetermined weight, resolution is reduced. That is, in the case where an amount of laundry increases to be equal to or greater than a predetermined level, as the amount of laundry increases, a discrimination capacity according to the weight of laundry is reduced. 
     A variation of the friction torque increases by friction between laundry and a door and upon jamming of the laundry at the door, and accordingly, the spread or dispersion of the friction torque increases. In particular, if an amount of laundry increases, the spread or dispersion of the friction torque increases significantly. 
     Due to movement of laundry, a deviation of the load torque occurs. In addition, if a weight of laundry is equal to or greater than a predetermined value, the movement of the laundry decreases and thus the load torque is reduced. 
     While the inertia torque is influenced by movement of laundry, the inertia torque has a linearity with respect to the amount (weight) of laundry and thus an amount of laundry may be measured more accurately. 
     Since the inertia torque is a force resisting to maintain the status quo, the inertia torque is applied upon acceleration or deceleration. That is, the inertia torque is applied in an acceleration stage and a deceleration stage, but, when a rotation speed is maintained constantly, the inertia torque is not applied and instead the motor torque, a friction torque, and the load torque are applied by gravity. 
     Thus, a property regarding the inertia torque may be calculated by excluding data of the maintaining stage from data of the acceleration stage. Inertia may be calculated by subtracting a current value of the maintaining stage from a current value of the acceleration stage and a current value of the deceleration period, dividing a result of the subtraction by a variation of speed per hour, that is, acceleration, and multiplying a result of the division by a counter electromotive force. 
     Thus, the dryer may determine an amount of laundry based on an inertia torque by analyzing a force applied in the acceleration stage and the maintaining stage, and the dryer may, in the maintaining stage, calculate a force of gravity according to the amount of the laundry. The inertia property is minimized in the maintaining stage, and the inertia greatly acts in the acceleration stage and the deceleration stage, and therefore, a final amount of laundry may be determined by calculating a laundry quantity sensing value for each stage based on different data and analyzing the calculated value in a comparative manner. 
     In addition, as the dryer calculates an amount of laundry by measuring a current value during rotation of the motor, a possibility of an error caused by a positional arrangement of the motor may be ruled out in operation, and, it is possible to minimize an error caused by a change in a load state in the maintaining stage, that is, a variation of the load, since the laundry moving regularly, not irregularly. 
       FIG. 12  is a diagram for explanation of movement of laundry in accordance with a rotation speed of a dryer according to an embodiment of the present disclosure. 
     As illustrated in  FIG. 12 , when sensing the amount of laundry  9 , the controller  110  rotates the drum  30  in a stopped state in any one direction so as to accelerate for a predetermined time period to a target rotation speed, maintains the target rotation speed for a predetermined time period, and then stops the drum. 
     Once the drum starts rotating, when a rotation speed is a low speed, the laundry  9  is in a state of rotating and rolling in the drum, as illustrated in (a) of  FIG. 12 , and, as the rotation speed increases, the laundry  9  is lifted up by the drum, increasing the amount of movement of the laundry  9 . 
     As illustrated in (b) of  FIG. 12 , if the rotation speed of the drum  30  increases, the laundry  9  is lifted by a centrifugal force of the drum and then dropped. 
     In addition, if the rotation speed of the drum further increases, the laundry  9  is stuck with the drum and thus rotates along with the drum  30 , as illustrated in (c) of  FIG. 12 . 
     As illustrated in (b) of  FIG. 12 , the controller  110  sets the target rotation speed to a degree of speed in which the laundry  9  moves along with the drum by the rotation of the drum  30  and is dropped from the top of the drum. 
     As illustrated in the drawing, if the rotation speed of the drum is a low speed, the amount of movement of the laundry is small, and, if the rotation speed of the drum increases, the laundry rotates along with the drum while being stuck with the drum by a centrifugal force. In order to dry the laundry, air should be allowed to pass through the laundry, and thus, at a time of sensing the amount of the laundry, a target rotation speed may be set to a rotation speed at which the laundry moves along with the drum and is dropped due to gravity acting greatly than the centrifugal force. The target rotation speed may be set identical to a normal rotation speed. 
     The rotation speed (target rotation speed) of the drum may be set in a range of 39 rpm to 63 rpm. At a time of measuring an amount of laundry, the drum may rotate at 57 rpm. In this case, if a pulley is provided in the motor with a ratio of 51:1, a rotation speed of the motor is 2000 rpm to 3200 rpm. 
     The controller  110  may change a rotation speed according to an amount of laundry. The controller  110  may classify the amount of laundry into multiple levels. 
     As the rotation speed of the motor changes, the rotation speed of the drum changes as well. However, according to the size, diameter, or circumference of the pulley of the motor connected to the drive belt of the drum and the size, diameter, or circumference of the drum, the rotation speed of the motor may change. 
     In addition, according to a sensed amount of laundry, the controller  110  may change a rotation speed in a drying operation. 
     In the drying operation, according to an amount of laundry, the controller may perform control with a first rotation speed, which is the basic rotation speed, and, when there is a great amount of laundry, a timing of dropping the laundry may be changed due to a weight of the laundry and a drying speed is slowed down, so, in this case, the rotation speed may be set to a second rotation speed higher than the first rotation speed. The second rotation speed is higher than the first rotation speed, and falls into a range of speeds at which some of the laundry in the drum are dropped and the others rotate along with the drum. 
     In addition, the controller  110  varies a rotation speed or a drying time based on a dryness degree of laundry, which is measured by the laundry sensing unit  132  during the drying operation. For example, in the case where an initially sensed amount of laundry is a few loads, when a dryness degree satisfies a preset value after the drying operation is performed for a preset time period, a rotation speed may be changed to a third rotation speed lower than the first rotation speed. In addition, when the dryness degree is smaller than a preset value after the drying operation is performed for the preset time period, the rotation speed may be changed to the second rotation speed. 
     For example, when an amount of laundry is a few loads or small loads, the controller  110  may set a rotation speed of the motor to 2900 rpm to 3000 rpm, and, when an amount of laundry is medium loads or large loads, the controller may set the rotation speed of the motor to 3000 rpm to 3200 rpm. In some cases, the small loads and the medium loads may be set to normal loads. In addition, according to an amount of laundry, a different rotation speed of the motor may be set. 
     In addition, during the drying operation, the controller  110  may change a rotation speed or a drying time according to an amount of laundry. In the case where the amount of laundry is a few loads, if a preset period of the drying time elapses, the rotation speed is changed to 2500 rpm to 2600 rpm according to a dryness degree sensed by the laundry sensing unit  132 . 
       FIG. 13  is a diagram for explanation of movement of laundry in a drum in accordance with the operation pattern shown in  FIG. 9 . 
     As illustrated in (a) to (d) of  FIG. 13 , at a time of sensing the amount (quantity) of laundry, the drum  30  repeatedly rotates forward or backward, and the controller  110  senses an amount of laundry based on a current value sensed by the current sensing unit  135 . 
     While driving the drum  30  to accelerate a rotation speed of the drum  30 , maintaining the rotation speed, and stopping the drum, the controller  110  measures current values for the acceleration stage and the maintaining stage, thereby sensing the amount of laundry. 
     In the case of performing the operation pattern once by rotating forward, the laundry in the drum is in a state of rotating and rolling during a period in which the rotation speed of the drum is accelerated. 
     As the rotation speed increases, the laundry in the drum is lifted by the drum and dropped, as shown in (b) and (d) of  FIG. 13 . 
     When the laundry is dropped, movement of the drum may occur, but this normally happens in the drying operation, so the controller  110  may measure the amount of laundry in a state in which the laundry is dropped. 
       FIG. 14  is a diagram for explanation of sensed properties in accordance with the amount of laundry in a dryer according to an embodiment of the present disclosure. 
     When measuring the amount of laundry, the dryer  1  repeatedly perform an operation pattern, including increasing a rotation speed of the drum, maintaining the increased rotation speed, and then stopping the rotation, a predetermined number of time. The dryer  1  divides the operation pattern into an acceleration stage in which the drum  20  accelerates the rotation speed thereof to a target rotation speed, a maintaining stage, and a stopping stage, and then measures current values for the respective periods. According to a degree of increase in the rotation speed in the acceleration stage, that is, an acceleration gradient, a deviation in measurements of laundry occurs. 
     As illustrated in  FIG. 14 , when it comes to measuring the amount of laundry, the controller  110  may calculate the amount of laundry by considering a linearity and a resolution calculated according to an acceleration gradient in relation to increase in the amount of laundry. 
     As illustrated in (a) of  FIG. 14 , as the acceleration gradient increases, the linearity increases. However, when the acceleration gradient increases, a slip between the drum  30  and the drive belt may occur, and therefore, it is preferable to accelerate rotation of the drum at a predetermined acceleration gradient or less. 
     When it comes to sensing an amount of laundry, a linearity refers to a degree of discrimination between calculated values according to the amount of laundry, and indicates a degree of increase in calculated values in proportion to increase in the amount of laundry. For example, the linearity indicates a degree of clearness in discrimination between a measurement obtained in response to 1 kg laundry and a measurement obtained in response to 2 kg laundry. 
     When the linearity is equal to or greater than 0.8, it is possible to discriminate an amount of laundry, and thus, in order to determine the amount of laundry, it is preferable to accelerate a rotation speed of the drum at an acceleration gradient with the linearity equal to or greater than 0.8. In order to more clearly determine the amount of laundry, it is preferable to control a rotation speed of the drum at an acceleration gradient equal to or greater than 0.82. 
     As shown in  FIG. 16  which will be described later, it is preferable that difference between calculated values is found big enough to discriminate according to an increase in the amount of laundry. 
     If the linearity is equal to or greater than 0.8, the acceleration gradient is equal to or greater than about 300 rpm/s. 
     If the linearity is equal to or greater than 0.82, the acceleration gradient is equal to or greater than about 450 rpm/s (p1). 
     As illustrated in (b) of  FIG. 14 , as an acceleration gradient is increased, a resolution is varied. The resolution refers to a deviation in measurements with respect to an amount (weight) of same laundry, and the resolution is a range of measurements according to an amount of laundry, as shown in  FIG. 16  which will be described later. If a range of measurements are wide with respect to the amount of the same laundry, there may be overlapping sections and thus it would be difficult to discriminate an amount of laundry. On the other hand, if a range of measurements is narrow with respect to the amount of the same laundry (if a deviation is small), it is easy to discriminate an amount of laundry in each section. 
     Thus, when it comes to sensing an amount of laundry, a resolution is preferably equal to or smaller than 1.5. 
     If the resolution is equal to or smaller than 1.5, an acceleration gradient for accelerating a rotation speed of the drum is 300 rpm/s (P2) to 1700 rpm/s (P3). 
     In the case where the linearity and the resolution are both considered, an acceleration gradient in an acceleration stage is preferably 300 rpm/s (P2) to 1700 rpm/s (P3) when it comes to determining the amount of laundry. With the linearity of 0.82 or greater, the acceleration gradient is preferably 500 rpm/s to 1700 rpms (P3). 
     If an acceleration gradient increases, a linearity increases but a resolution decreases (a value thereof increases), and thus, the acceleration gradient is preferably set to 300 rpm/s (P2) to 1700 rpm/s (P3). 
     According to a resolution graph, it is found that good performance is achieved at the acceleration gradient of 500 rpm/s to 100 rpm/s and 1250 rpm/s to 1500 rpm/s. In addition, in the case where the acceleration gradient is 100 rpm/s to 1250 rpm/s, performance degradation may occur due to idling of the motor, but this degradation is merely a change in performance still falling within a range in which linearity and resolution satisfy set values, and therefore, such an acceleration gradient is applicable. The linearity and the resolution may vary depending on a structure of connection between the drum and the motor, and characteristics of the motor. 
       FIGS. 15 to 17  are graphs illustrating results of sensing an amount of laundry in a dryer according to an embodiment of the present disclosure. 
     Results on calculation of an amount of laundry according to an acceleration gradient is as follows. The drawings show measurements obtained based on the same laundry having moisture content of 66.6%. 
     An amount of laundry measured at an acceleration gradient of 250 rpm/s is shown in (a) of  FIG. 15 , and the amount of laundry measured at an acceleration gradient of 1750 rpm/s is shown in (b) of  FIG. 15 . 
     As illustrated in (a), when the acceleration gradient is 250 rpm/s, a linearity is low because of small difference between measurements in sections according to an amount of laundry, and a resolution is low because of a wide range (a great deviation) of measurements with respect to an amount of the same laundry. For example, weight measurements are redundant in sections corresponding to 1 kg to 2 kg (92) and sections corresponding to 5 kg or more (91), and thus, it is difficult to discriminate an amount of laundry. 
     As illustrated in (b) of  FIG. 15 , when the acceleration gradient is 1750 rpm/s, a good linearity is achieved with respect to a small amount of laundry, but the linearity and the resolution are both low in sections corresponding to 3 kg or more (93). 
     An amount of laundry measured at an acceleration gradient of 500 rpm/s is shown in (a) of  FIG. 16 , and an amount of laundry measured at an acceleration gradient of 750 rpm/s is shown in (b) of  FIG. 16 . (a) of  FIG. 17  an amount of laundry measured at an acceleration gradient of 1000 rpm/s is shown in (a) of  FIG. 17 , an amount of laundry measured at an acceleration gradient of 1250 rpm/s is shown in (b) of  FIG. 17 , and an amount of laundry measured at acceleration gradient of 1500 rpm/s is shown in (c) of  FIG. 17 . 
     As illustrated in (a) and (b) of  FIG. 16  and (a) to (c) of  FIG. 17 , a linearity and a resolution satisfy ranges respectively set therefor when the acceleration gradient are 500 rpm/s, 750 rpm/s, 1000 rpm/s, 1250 rpm/s, and 1500 rpm/s. 
     For example, when the acceleration gradient is 750 rpm/s, the linearity is excellent because of enough difference between measurements according to an amount of laundry, and a resolution is excellent because of a narrow range of measurements with respect to the amount of the same laundry. 
     Therefore, when measuring an amount of laundry, the controller  110  may set an acceleration gradient in the acceleration stage to be fall within a range of 500 rpm/s to 1500 rpm/s. In particular, the controller  110  may control the acceleration stage with the acceleration gradient of 750 rpm/s. 
       FIG. 18  is a flowchart illustrating a method of controlling a dryer according to an embodiment of the present disclosure. 
     As illustrated in  FIG. 18 , the dryer  1  operates such that laundry is loaded into the drum  30  and a mode according to a drying operation is set by the operator  170  (S 310 ). For example, a mode is set according to a type of the laundry, especially according to a material of the laundry, such as silk, cotton, or the like. 
     The controller  110  senses the amount (quantity) of the laundry by controlling the driver  160  (S 320 ). The driver  160  rotates the drum in accordance with a control command, and, once the drum rotates in accordance with a pattern, the current sensing unit  135  measures a current value of the motor. 
     The controller  110  may store a current value, sensed by the current sensing unit, for each of the acceleration and the maintaining stage on the basis of each number of times, that is, on a per round-of-pattern basis. 
     The controller  110  sets a drying time according to the amount (quantity) of laundry (S 330 ). The set drying time is displayed on a display of the output unit  175 . 
     The controller  110  determines an amount of laundry to be one of multiple levels, and sets a preset drying time according to the determined amount of the laundry. 
     The driver  160  performs the drying operation such that the motor is driven in accordance with a control command from the controller, thereby rotating the drum and operating the blow fan (S 340 ). 
     During the drying operation, the drum lifts the laundry and lets the laundry fall repeatedly. During the rotation of the drum, air circulated by the blow fan  64  is heated up by the condenser  52  or the heater  69  of the heat pump module  120  and then supplied to the drum, and moisture evaporated from the laundry is contained in the air and flows to the evaporator through the circulation flow path by the blow fan. As a refrigerant and air having high moisture content are thermally exchanged in the evaporator, the air is cooled down and the moisture contained in the air is condensed, thereby generating condensate. Humidified air flows to the condenser, and is heated up and then supplied back to the drum. 
     The laundry sensing unit  132  disposed at a lower end in the entry hole senses a dryness degree of laundry in response to a current flowing at a time when two electrodes  18  contact the laundry, and inputs a predetermined signal to the controller (S 350 ). 
     The controller determines whether the dryness degree of the laundry is equal to or greater than a set value, that is whether the amount of moisture contained in the laundry is equal to or greater than a predetermined value (S 360 ). 
     At a time when a preset period of the drying time has elapsed, if the dryness degree is smaller than the set value, the controller  110  changes an operation setting (S 370 ) and keeps performing the drying operation (S 340 ). The controller  110  may extend the drying time or change a rotation speed of the drum. 
     At a time when the preset period of the drying time has elapsed, if the dryness degree is equal to or greater than the set value, the controller  110  maintains the current operation state. 
     If the drying time has elapsed (S 380 ), the controller  110  outputs a drying operation termination notification through the output unit  175  (S 390 ). The controller  110  outputs the termination notification through a display and output notification sound through a speaker according to termination of the drying operation. In some cases, the controller  110  may transmit a notification message to a connected terminal. 
       FIG. 19  is a diagram illustrating a control method in accordance with the amount of laundry in a dryer according to an embodiment of the present disclosure. 
     As illustrated in  FIG. 19 , an amount of laundry in the drum is sensed (S 410 ). 
     The controller  110  determines whether the amount of laundry corresponds to large loads (S 420 ). If the weight of laundry is equal to or greater than a predetermined value, large loads is determined, and if the weight of the laundry is smaller than the predetermined value, small loads or medium loads is determined, and, if the amount of laundry is small, a few loads is determined additionally. 
     The controller  110  applies a control command to the driver  160  so as to perform a drying operation at a first rotation speed in the case of the small loads or the few loads (s 430 ) and perform the drying operation at a second rotation speed in response to the medium loads or the large loads (S 450 ). The second rotation speed may be set to a rotation speed within a range of speeds at which laundry with normal loads is lifted and dropped, wherein some of the laundry rotate along with the drum and the others are dropped. The normal loads is used as a reference because, in the case of the large loads, there is a great amount of laundry and hence the laundry may be dropped even at the same rotation speed due to a weight of the laundry. 
     The driver  160  performs the drying operation by performing control in accordance with the control command from the controller such that the drum rotates at a set rotation speed and air is circulated by the blow fan. The heat pump module  120  or the heater  69  heats up air being supplied to the drum  30 . 
     The laundry sensing unit senses a dryness degree of laundry moving in the drum (S 460 ), while contacting the laundry. The laundry sensing unit measures the dryness degree using difference in current values measured according to an amount of moisture contained in the laundry in contact, and inputs the measured dryness degree to the controller. 
     After the drying operation is performed for a preset time period or more (S 470 ), the controller  110  determines whether the measured dryness degree is equal to or greater than a preset value (S 480 ). 
     Until the preset period elapses, the drying operation is maintained even when the dryness degree is smaller than the preset value. 
     After the preset period elapses, if the dryness degree of the laundry is smaller than the preset value, the controller  110  increases a rotation speed of the drum. The controller  110  increases the rotation speed of the drum to the second rotation speed. In the case of the large loads, the drum is already operating at the second rotation speed and hence the controller  110  somewhat accelerates the rotation speed within the above-described rotation speed range to increase the rotation speed, or increases the drying time. 
     After the preset period elapses, if the dryness degree of the laundry is equal to or greater than the preset value and the amount of laundry is equal to or greater than small loads and smaller than large loads, the controller  110  maintains the current setting and performs the drying operation (S 510 ). 
     Meanwhile, after the preset period elapses, if the dryness degree of the laundry is equal to or greater than the preset value and the amount of laundry is a few loads, the controller  110  changes the rotation speed of the drum to a third rotation speed lower than the first rotation speed (S 500 ) in order to prevent the laundry from being dried too much or to save energy. According to the changed setting, the drying operation is performed (S 510 ) until the end of the drying time. 
     Accordingly, the present disclosure determines an amount of laundry by measuring currents in an acceleration stage in which a rotation speed of motor increases during rotation of the drum and in a maintaining stage in which the rotation speed of the motor is maintained, thereby enabled to minimize influence of friction and more accurately determine the amount of laundry using inertia properties. 
     In addition, the present disclosure changes the rotation speed during a drying time or a drying operation according to an amount of laundry, thereby reducing the operation time or saving energy and thus drying the laundry efficiently. 
     Although all components of the embodiments are described as operating in combination with each other as one body, the present disclosure is not necessarily limited to the embodiments described above. According to embodiments, one or more of all components may be selectively combined without departing from the spirit of the present disclosure. 
     The foregoing description is merely an illustrative example of the technical idea of the present disclosure, and any person skilled in the art may make various modification and variations without departing from the spirit of the present disclosure.