Patent Publication Number: US-2009223230-A1

Title: Method of controlling ice making assembly for refrigerator

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. 119 and 35 U.S.C. 365 to Korean Patent Application No. 10-2008-0021817, filed Mar. 10, 2008, which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     The present disclosure relates to a method of controlling an ice making assembly for a refrigerator for making transparent ice. 
     Refrigerators are domestic appliances used for storing foods in a refrigerated or frozen environment. 
     Recently, various kinds of refrigerators have been introduced into the market. Examples of recent refrigerators include: a side-by-side type refrigerator in which a refrigerator compartment and a freezer compartment are disposed in the left and right sides; a bottom-freezer type refrigerator in which a refrigerator compartment is disposed above a freezer compartment; and a top-mount type refrigerator in which a refrigerator compartment is disposed under a freezer compartment. 
     Furthermore, many of recently introduced refrigerators have a structure that allows a user to access food or drink disposed inside a refrigerator compartment through an alternate access point without having to open a primary refrigerator compartment door. A compressor, a condenser, and an expansion member are disposed inside a refrigerator, and an evaporator is disposed on the backside of a refrigerator main body, as refrigeration-cycle components of the refrigerator. 
     In addition, an ice making assembly can be provided inside the refrigerator. The ice making assembly may be mounted in a freezer compartment, a refrigerator compartment, a freezer compartment door, or a refrigerator compartment door. 
     To satisfy consumers&#39; increasing demands for transparent ice, much research has been conducted on ice making assemblies that can provide transparent ice. 
     SUMMARY 
     The disclosed embodiments provide a method of controlling an ice making assembly for a refrigerator that can produce transparent ice. 
     The disclosed embodiments provide methods of controlling an ice making assembly for a refrigerator. 
     In one embodiment, there is provided a method of controlling an ice making assembly for a refrigerator, the method including: selecting an ice making mode; supplying water to an ice recess formed in a tray so as to immerse a rod configured to take heat from the water; intermittently operating a heater disposed at the tray to maintain the tray at a temperature higher than a freezing temperature; and controlling an operation of a cooling fan configured to supply cooling air so as to cool the rod. 
     In another embodiment, there is provided a method of controlling an ice making assembly for a refrigerator, the method including: selecting an ice making mode; supplying water to an ice recess formed in a tray so as to immerse a rod configured to take heat from the water; intermittently operating a heater disposed at the tray to maintain the tray at a temperature higher than a freezing temperature; and controlling an operation of an ice ejecting heater configured to heat the rod so as to decrease a temperature of the rod with time. 
     In another embodiment, there is provided a method of controlling an ice making assembly for a refrigerator, the method including: selecting an ice making mode; supplying water to an ice recess formed in a tray so as to immerse a rod configured to take heat from the water; intermittently operating a heater disposed at the tray to maintain the tray at a temperature higher than a freezing temperature; and controlling cooperative operations of an ice ejecting heater configured to heat the rod and a cooling fan configured to supply cooling air so as to decrease a temperature of the rod with time. 
     According to the method of controlling the ice making assembly, transparent ice can be made in an ice making compartment that is kept at a temperature lower than 0° C. 
     That is, the tray is kept at a temperature higher than 0° C. during an ice making operation to freeze water slowly and to ensure that the water freezes in a direction starting from the rod toward the inner surface of the ice recess. Therefore, while the freezing of the water proceeds, air dissolved in the water can escape from the water before the air is trapped in the ice. The resulting ice that is made is thus transparent. 
     Furthermore, during an ice making operation, the temperature of water may be adjusted by controlling the cooling fan and the temperature of the freezing rod so that bubbles contained in the water can escape during the ice making operation. Transparent ice can be readily made. 
     The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 and 2  are perspective views illustrating an ice making assembly structure for a refrigerator according to an embodiment of the invention. 
         FIG. 3  is a perspective view illustrating an ice making assembly according to an embodiment of the invention. 
         FIG. 4  is a perspective view illustrating the ice making assembly, according to an embodiment of the invention, just before ice is transferred to a container. 
         FIG. 5  is a perspective view illustrating a tray of the ice making assembly according to an embodiment of the invention. 
         FIG. 6  is a sectional view illustrating a process of making transparent ice in the ice making assembly according to an embodiment of the invention. 
         FIG. 7  is a flowchart depicting a method of controlling the temperature of a tray of an ice making assembly according to an embodiment of the invention. 
         FIG. 8  is a flowchart depicting a method of making transparent ice using an ice making assembly according to a first embodiment of the invention. 
         FIG. 9  is a flowchart depicting a method of making transparent ice using an ice making assembly according to a second embodiment of the invention. 
         FIG. 10  is a flowchart depicting a method of making transparent ice using an ice making assembly according to a third embodiment of the invention. 
         FIG. 11  is a graph illustrating the temperature of a rod when a method of controlling an ice making assembly is performed according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, an ice making assembly for a refrigerator will be described in detail according to embodiments of the present disclosure with reference to the accompanying drawings, 
     In the following description, an ice making assembly may be mounted at a freezer compartment door. However, the ice making assembly can be mounted at other places such as a freezer compartment, a refrigerator compartment, and a refrigerator compartment door and still be within the scope of the invention. 
       FIGS. 1 and 2  are perspective views illustrating an ice making assembly structure for a refrigerator according to an embodiment of the invention. 
     Referring to  FIGS. 1 and 2 , an ice making assembly  20  of the exemplary embodiment may be mounted on the backside of a door  10 , and the backside of the door  10  may be recessed to form an ice making space  11  that accommodates the ice making assembly  20 . A cooling air supply hole  111  ( FIG. 2 ) may be formed at a side of the ice making space  11  to allow inflow of cooling air from an evaporator (not shown), and a cooling air discharge hole  112  ( FIG. 2 ) may be formed in the side of the ice making space  11  to allow the cooling air from the ice making space  11  to flow back to the evaporator. 
     In detail, the ice making assembly  20  may be mounted at an upper portion of the ice making space  11 , and a container  30  may be mounted under the ice making assembly  20  to store ice made by the ice making assembly  20 . The ice making assembly  20  may be protected by an ice making cover  31 . The ice making cover  31  may also provide guidance for the ice separated from the ice making assembly  20  so that it follows a path directly to the container  30 . 
       FIG. 3  is a perspective view illustrating the ice making assembly  20  according to an embodiment of the invention, and  FIG. 4  is a perspective view illustrating the ice making assembly  20 , according to an embodiment of the invention, just before ice is transferred to the container  30 . 
     Referring to  FIGS. 3 and 4 , the ice making assembly  20  may include: a tray  21  having a plurality of ice recesses  211  for making ice in a predetermined shape; a plurality of fins  24  stacked above the tray  21  and capable of vertical and rotational movement; a plurality of rods  23  configured to be inserted into the ice recesses  211  through the fins  24 ; an ice ejecting heater  25  may be provided as the lowermost fin of the plurality of fins  24 ; a supporting plate  27  configured to support the ice ejecting heater  25 , the remainder of the plurality of fins  24 , and the rods  23  as one unit; a water supply part  26  disposed at an end of the tray  21 ; and a control boxy  28  disposed at another end of the tray  21 . 
     In detail, a heater (not shown) may be mounted at the bottom of the tray  21  to maintain the temperature of the tray  21  at a temperature above freezing. A supporting lever  271  may extend from a front end of the supporting plate  27 , and a hinge  272  may be disposed at an end of the supporting plate  27 . During an ice making operation, as shown in  FIG. 4 , ice cubes (I) having a shape corresponding to the shape of the ice recesses  211  are formed around the rods  23 . 
     A cam  29  coupled to a driving motor are disposed inside the control box  28 . The driving motor drives a rotational movement of the cam  29 . The hinge  272  may be coupled to the cam  29  so that the hinge  272  can be lifted and rotated by the rotation of the cam  29 . The ice ejecting heater  25  may have a plate-like shape and may make contact with the rods  23 . Alternatively, the ice ejecting heater  25  may be buried in the rods  23 . The supporting plate  27  may act to close an open-top of the tray  21  (see  FIG. 3 ) such that water supplied to the tray  21  is indirectly cooled by cooling air that is supplied to the ice making space  11  and flows about fins  24  and rods  23 . 
     Hereinafter, ice making and ice ejecting operations of the ice making assembly  20  will be described. 
     First, the heater attached to the tray  21  may be operated to maintain the tray  21  at a temperature higher than 0° C. so as to make transparent ice in the ice making assembly  20 . 
     In the related art when water is rapidly frozen by cooling air supplied from an evaporator, air dissolved in the water cannot escape from the water before it freezes. Thus, when water is frozen together with gas that is trapped inside the water, the resulting ice will not be transparent. 
     However, in the ice making assembly  20  of the disclosed exemplary embodiments, the tray  21  may be kept at a temperature above freezing so that the water freezes slowly. The air in the water is then able to escape before the water is completely frozen. Thus resulting in transparent ice, which is preferred by the user. Once the rods  23  are inserted in the ice recesses  21   1  of the tray  2   1 , water is supplied to the tray  2   1 , and a freezing operation is started after the supply of water is completed. The freezing operation is started by supplying cooling air to the ice making space  1   1 . Then, the temperature of the fins  24  is reduced to below freezing by convection heat transfer with the supplied cooling air. The temperature of the rods  23  is also reduced to below freezing by conduction heat transfer with the fins  24 . Portions of the rods  23  inserted in the ice recesses  21   1  are submerged in the water. Therefore, the water may be gradually frozen starting from a region closest to the rods  23 , and the frozen region of the water becomes attached to the rods  23 . Then, the freezing of the water further proceeds outwardly from a region closest to the rods  23  toward a region close to the inner surfaces of the ice recesses  211 . 
     After the water is completely frozen, the cam  29  is rotated to move the rods  23 , and the ice cubes formed thereon, vertically upward out of the ice recesses  211 . In the exemplary embodiment, after the ice cubes (I) are completely removed from the ice recesses  211 , the cam  29  is further rotated to rotate the rods  23  at a predetermined angle so that the ice cubes (I) can slip off of the rods  23  and fall into an ice container  30 . 
     Whether freezing of the water is completed may be determined by several methods. A first method involves monitoring time lapsed while the water is freezing. If a predetermined amount of time passes after the start of the freezing, it may be determined that the freezing is completed. 
     Another method of determining the completion of freezing involves lifting the rods  23 , via cam  29 , out of the recesses  211 , and detecting an amount of water remaining in the recesses  211 . The rods  23  may be lifted to a predetermined height after a predetermined amount of time has passed from the start of freezing. The predetermined height may be a height at which ice attached to the rods  23  is not yet fully separated from the ice recesses  211 . Once the rods  23  are lifted, the amount of water remaining in the ice recesses  21  may be detected. The amount of unfrozen water remaining in the ice recesses  211  can be detected, for example, using a water level sensor (not shown) mounted on the tray  21 . If the amount of unfrozen water remaining in the ice recesses  211  is equal to or less than a predetermined amount, it may be determined that the freezing is completed. On the other hand, if the amount of unfrozen water remaining in the ice recesses  211  is greater than the predetermined amount, the rods  23  may be moved down to their original positions to continue freezing the water. The water sensor will be described later with reference to the accompanying drawings. 
     As described above, after the freezing of the water is completed, the cam  29  may be rotated such that it moves the rods  23 , and the ice cubes formed thereon, vertically upward out of the ice recesses  211 . After ice cubes (I) are completely removed from the ice recesses  211 , the cam  29  may be further rotated to effect rotation of the rods  23 . More specifically, the hinge  272  may be rotated by the cam  29  to rotate the rods  23  at a predetermined angle. Once the rods  23  are rotated to a predetermined angle as shown in  FIG. 4 , the ice ejecting heater  25  may be operated. When the ice ejecting heater  25  is operated, the temperature of the rods  23  is increased, and thus the ice cubes (I) are separated from the rods  23 . The separated ice cubes (I) may thus fall into the container  30 . 
       FIG. 5  is a perspective view illustrating the tray  21  of the ice making assembly  20  according to an embodiment of the invention. 
     As illustrated in  FIG. 5 , the ice recesses  211  are arranged in the tray  21  of the ice making assembly  20 . Grooves  213  having a predetermined depth are formed between the ice recesses  211 . Water can travel between neighboring ice recesses  211  through the grooves  213 . Bottoms of the grooves  213  are spaced apart from bottoms of the ice recesses  211 . 
     A guide  212  may be formed at an end portion of the tray  21  to guide water supplied from the water supply part  26  to the tray  21  and to the ice recesses  211 . Water may be supplied to the ice recesses  211  closest to the guide  212  and may gradually travel to the ice recess  211  farthest from the guide  212 . 
     A water level sensor  40  may be mounted at a side of the ice recess  211  farthest from the guide  212 , e.g., at a side of the ice recess located at an end of the tray  21  opposite to the guide  212 . Further, a temperature sensor  50  may be mounted at a side of the tray  2   1 . The temperature sensor  50  may provide feedback to a subsystem adapted to maintain the tray  21  at a constant temperature. A tray heater (not shown) may be installed at the tray  21 . The tray heater may be installed at the tray  21  in an embedded or attached manner. 
       FIG. 6  is a sectional view illustrating a process of making transparent ice in the ice making assembly  20  according to an embodiment of the invention. 
     Referring to  FIG. 6 , in the exemplary embodiment, a tray heater  60  may be installed in the tray  21  of the ice making assembly  20 . After the rod  23  is moved down to a preset position, the ice recess  211  is filled with water. Alternatively, the rod  23  can be moved down to the preset position after the ice recess  211  is filled with water. 
     Once the rods  23  are in position, and the ice recesses contain a sufficient volume of water, an ice making operation can begin. The fins  24  are cooled by cooling air that is circulated to cool the tray  21  and rods  23  to below freezing by convection heat exchange with the fins  24 . When the temperature of the rod  23  drops below freezing, ice is formed around the rod  23 . At this point, the tray heater  60  operates to maintain the tray  21  at a temperature above 0° C. According to an exemplary embodiment, the tray  21  may be kept at a temperature in the range of 1° C. to 2° C. According to Henry&#39;s Law, the solubility of gas in water is reduced as the temperature of the water increases. Therefore, air present in the water can be removed from the water as it freezes by operating the tray heater  60 . At the same time, ice grows from the surface of the rod  23 . 
     During the ice making process, ice forms outwardly from the surface of rod  23  while the tray  21  is kept at a temperature above freezing. Therefore, ice cannot form at the inner surface of the tray  21 . In other words, ice cannot form on the inner surface of an ice recess  211 . Accordingly, when the ice making operation is completed a predetermined amount of water may remain in the ice recess  211 . The removal of the ice cubes from the tray  21  is facilitated in an embodiment where water remains in an unfrozen state just adjacent to the inner surface of the ice recess  211 . 
     A rod temperature sensor  70  may be disposed in the rod  23 . Thus, when the rod  23  is heated by the ice ejecting heater  25  ( FIG. 4 ) during an ice ejecting operation, the temperature increase of the rod  23  can be controlled to reach a set temperature. It is also envisioned that during an ice making operation, the rod  23  may be heated to temporarily increase the temperature of water present in the tray  21 , so as to allow air trapped in the water to escape. 
     Other methods are within the scope of the invention. For example, in another method, a cooling fan (not shown), configured to supply cooling air to the inside of the ice making space  11 , may be controlled. In yet another method, the ice ejecting heater  25 , configured to heat the rod  23 , and the cooling fan may be both simultaneously operated and controlled. A method of controlling the temperature of water filled in the tray  21  for making transparent ice will now be described with reference to a flowchart. 
       FIG. 7  is a flowchart depicting a method of controlling the temperature of a tray of an ice making assembly according to an embodiment of the invention 
     Referring to  FIG. 7 , an ice making mode may be started by a user or a control unit (see e.g., ref  45  of  FIG. 3 ) associated with the refrigerator (operation S 11 ) in general or the ice making assembly in particular. 
     By way of example, the ice making mode can be initiated by the control unit  45  when an automatic ice making operation is necessary; for example, when a low amount of ice in ice container  30  is detected. 
     After the ice making mode begins, or even continuously, the control unit  45  receives a signal from a temperature sensor, such as temperature sensor  50  of  FIG. 5 , to determine the temperature of the tray  21 . The control unit  45  may determine whether the temperature T of the tray  21  is at a predetermined temperature T 0 . For example, the control unit  45  may determine whether the tray temperature T is lower or higher than the predetermined temperature T 0  (operation S 12 ). 
     If the tray temperature T is lower than the predetermined temperature T 0 , the tray heater  60  may be turned on to heat the tray  21  (operation S 13 ). On the other hand, if the tray temperature T is equal to or greater than the predetermined temperature T 0 , the tray heater  60  may be turned off (operation S 14 ). Here, turning-off of the tray heater  60  includes the case where the tray heater  60  is previously turned off and kept in the turned-off state. 
     As the tray heater  60  is controlled as described above, the control unit  45  may also determine whether ice making is completed (operation S 15 ). An exemplary method of determining whether ice making is complete is as discussed above. 
     If it is determined that ice making is complete, the ice making mode is turned off (operation S 16 ) to complete the ice making operation. On the other hand, if it is determined that ice making is not completed, operations S 12 , S 13 , and S 14  may be repeated. Thus, the on-off control of the tray heater  60  continues until the ice is satisfactorily formed. 
     By using the above-described control method, the tray  21  can be kept at a temperature above freezing temperature while ice is forming around the control rod  23 , thus resulting in transparent ice. 
       FIG. 8  is a flowchart depicting a method of making transparent ice using an ice making assembly according to a first embodiment of the invention. Referring to  FIG. 8 , in the exemplary embodiment, the temperature of water supplied to the tray  21  is controlled by controlling the operation of a fan during an ice making operation. 
     In detail, according to the above-described gas solubility properties, air contained in water may be trapped in the water as it freezes if the temperature of the water drops too quickly. To prevent this, the temperature of the water is temporarily raised to allow the air to escape. 
     First, when an ice making mode is turned on (operation S 2   1 ), water is first supplied (operation S 22 ). Before an ice making operation begins after the water supply operation, a control unit  45  determines whether the measured temperature T of the rod  23  is equal to or greater than a first predetermined temperature T 1  (operation S 24 ). Here, the temperature T of the rod  23  may be the surface temperature of the rod  23 , which may be detected using the rod temperature sensor  70  ( FIG. 6 ). If it is determined that the temperature T of the rod  23  is equal to or greater than the first temperature T 1 , the cooling fan may be turned on to lower the temperature of rod  23  (operation S 25 ). On the other hand, if it is determined that the temperature T of the rod  23  is lower than the first temperature T 1 , the cooling fan may be turned off (operation S 26 ) to prevent cool air circulation in the ice making space  11 . Here, turning-on (S 25 ) or turning-off (S 26 ) includes the situation where the cooling fan may be previously turned on or off and is maintained in the turned-on or turned-off state, respectively. For example, if it is determined that the rod temperature T is equal to or greater than the first temperature T 1  and the cooling fan is in an turned-on state, the cooling fan may simply be left in the turned-on state. 
     Once the cooling fan operation has been determined, the control unit determines whether ice making time (t) has reached a first set time t 1  (operation S 27 ).  10068 J In detail, if it is determined that the ice making time, e.g., the time passed since the ice-making operation began (t), has not reached the first set time t 1 , the procedure may go back to operation S 24 . On the other hand, if it is determined that the ice making time (t) has reached the first set time t 1 , the rod  23  temperature may then be controlled. 
     More specifically, after the ice making time reaches the first set time t 1 , it is then determined whether the rod temperature T is equal to or greater than a second predetermined temperature T 2  (operation S 28 ). The second predetermined temperature T 2  may be lower than the first predetermined temperature T 1 . If it is determined that the rod temperature T is equal to or greater than the second temperature T 2 , the cooling fan may be turned on (operation S 29 ). Otherwise, the cooling fan may be turned off (operation S 30 ). These operations are generally the same as those operations using the first temperature. 
     While keeping the rod temperature T below the second temperature T 2 , it is determined whether the ice making time (t) has reached a second set time t 2  (operation S 31 ). 
     When it is determined that the ice making time (t) reaches the second set time t 2 , an ice ejecting operation may be performed (S 32 ). After the ice ejecting operation, the ice making mode may be turned off (operation S 33 ). If the ice making time (t) has not reached the second set time t 2 , the procedure will go back to operation S 28 . 
     In the first embodiment, a control process may be carried out to make transparent ice using the cooling fan without turning on the ice ejecting heater  25 . While the “on/off” control of the cooling fan is discussed above, the speed of the cooling fan can also be controlled depending on the measured temperature of the rod  23 . In this situation, a variable speed fan motor may be used. 
     The temperature of the rod  23  may be reduced slowly, in steps, to prevent trapping air in the water as it freezes. In the exemplary embodiment the temperature T of the rod  23  is reduced in two steps, however, three or more steps may be used according to, for example, freezer compartment conditions. 
       FIG. 9  is a flowchart depicting a method of making transparent ice using an ice making assembly according to a second embodiment. 
     Referring to  FIG. 9 , in the exemplary embodiment, the temperature of water supplied to the tray  21  may be controlled via the ice ejecting heater  25 . The cooling fan may be kept on i.e., continuously operated, while the ice-ejecting heater  25  is controlled to adjust the temperature of rod  23 . 
     First, the ice making mode is initiated (operation S 51 ), water is supplied (operation S 52 ), and the water supply is completed (operation S 53 ) similar to the first embodiment. 
     After the water supply is completed, the cooling fan may be operated to supply and circulate cooling air throughout the ice making space  11  (operation S 54 ). The plurality of fins  24  are cooled by convection heat transfer with the cooling air, and the rod  23  may be cooled by conduction heat transfer with the cooled fins  24 . 
     The surface temperature of the rod  23  may be measured by the rod temperature sensor  70  and may be transmitted to the control unit  45 . Then, the control unit  45  determines whether the measured rod temperature T is equal to or greater than a first predetermined temperature T 1  (operation S 55 ). 
     In detail, if it is determined that the rod temperature T is equal to or greater than the first temperature T 1 , the ice ejecting heater  25  may be turned off (operation S 56 ). Otherwise, the ice ejecting heater  25  is turned on (operation S 57 ). Here, turning the ice ejecting heater  25  on or off is similar to the above-described “on/off” function of the cooling fan. 
     After the on/off operation of the ice ejecting heater  25  is determined and a predetermined time has passed, the control unit may determine whether ice making time (t) reaches a first set time t 1  (operation S 58 ). If the ice making time (t) has not reach the first set time t 1 , the procedure goes back to operation S 55 . 
     On the other hand, if the ice making time (t) has reached the first set time t 1 , the temperature T of the rod  23  is then reduced to a temperature lower than the first set temperature T 1 . 
     In more detail, once the ice making time (t) reaches the first set time t 1 , the current rod temperature T may be measured. It is then determined if this measured rod temperature T is equal to or greater than a second predetermined temperature T 2  (operation S 59 ). Here, the second temperature T 2  may be lower than the first set temperature T 1 . If the rod temperature T is equal to or greater than the second temperature T 2 , the ice ejecting heater  25  may be turned off (operation S 60 ). Conversely, if the rod temperature T is lower than the second set temperature T 2 , the ice ejecting heater  25  may be turned on (operation S 61 ). 
     Then, it is determined whether the ice making time (t) has reached a second set time t 2  (operation S 62 ). This time passage determination may be conducted while the temperature T of the rod  23  is maintained at the second set temperature T 2 . 
     As illustrated in  FIG. 9 , if the ice making time (t) has not reached the second set time t 2 , the procedure goes back to operation S 59 . Conversely, if the ice making time (t) has reached the second set time t 2 , an ice ejecting operation may be performed (S 63 ). After the ice is ejected, the ice making mode may be turned off (operation S 64 ). 
     According to the above-described method, the ice ejecting heater  25  may be used to control the ice-making environment to make transparent ice. That is, if the rod temperature T is reduced to below a temperature suitable for making transparent ice, the ice ejecting heater  25  is turned on to heat the rod  23 . Therefore, the temperature of water filled in the tray  21  may be properly controlled so that air contained in the water can escape as the water freezes. 
     In the second exemplary embodiment, the temperature of water filled in the tray  21  may be adjusted by controlling the ice ejecting heater  25 . However, the method of the present disclosure is not limited to this. For example, a voltage applied to the ice ejecting heater  25  can be controlled using a semiconductor switch device, such as a TRIAC or a thyristor. In this case, if the temperature T of the rod  23  is lower than a set temperature T 1  or T 2 , the amplitude of the voltage applied to the ice ejecting heater  25  may be increased to generate more heat. Conversely, if the temperature T is higher than a set temperature the amplitude of the voltage applied to the ice ejecting heater  25  may be reduced to generate less heat. Further, the temperature T of the rod  23  may be steadily (continuously) reduced instead of being reduced in a stepped manner. 
       FIG. 10  is a flowchart depicting a method of making transparent ice using an ice making assembly according to a third embodiment. 
     As illustrated in  FIG. 10 , in the exemplary embodiment, the temperature of water supplied to the tray  21  may be controlled by cooperatively operating the ice ejecting heater  25  and the cooling fan. 
     First, it is noted that turning on the ice making mode (operation S 71 ), water supply (operation S 72 ), and completion of water supply (operation S 73 ) are performed in the same way as in the first embodiment. 
     In detail, after water supply is completed, it is determined whether the temperature T of the rod  23  is equal to or greater than a first predetermined temperature T 1  (operation S 74 ). If the detected rod temperature T is equal to or greater than the first temperature T 1 , the cooling fan may be turned on and the ice ejecting heater  25  may be turned off (operation S 75 ). Thus, cooling air may be supplied to the ice making space  11 , to cool the rod  23  to the first temperature T 1 . Conversely, if the rod temperature T is lower than the first temperature T 1 , the cooling fan may be turned off and the ice ejecting heater  25  may be turned on to keep the rod temperature T at approximately first temperature (operation S 76 ). 
     While the rod temperature T is maintained at approximately the first temperature T 1 , as described above, the control unit  45  determines whether the time that passed since the ice making process began, i.e., ice making time (t), has reached a first set time t 1  (operation S 77 ). If the ice making time (t) has not reached the first set time t 1 , the procedure will go back to operation S 74 . 
     Conversely, if the ice making time (t) has reached the first set time t 1 , the temperature T of the rod  23  is reduced to and kept at a temperature lower than the first temperature T 1 . That is, it is determined whether the rod temperature T is equal to or greater than a second predetermined temperature T 2  (operation S 78 ). Here, the second temperature T 2  is less than the first temperature T 1 . 
     In detail, if the rod temperature T is equal to or greater than the second temperature T 2 , the cooling fan may be turned on and the ice ejecting heater  25  may be turned off (operation S 79 ). On the other hand, if the rod temperature T is below the second temperature T 2 , the cooling fan may be turned off and the ice ejecting heater  25  may be turned on (operation S 80 ). Once the rod temperature T reaches the second temperature T 2 , the amount of time that has passed, i.e. an ice-making time (t), is compared to a second set time t 2 . Based on this comparison it is determined whether the ice making time (t) has reached a second set time t 2  (operation S 81 ). If the ice making time (t) has not yet reached the second set time t 2 , the procedure goes back to operation S 78 . 
     If the ice making time (t) has reached the second set time t 2 , the ice making operation is completed and the ice is then ejected (S 82 ). After the ice ejecting operation is complete, the ice making mode is turned off (operation S 83 ). It is noted that for the method described above the temperature T of the rod  23  may be reduced in a stepped manner or in a continuous/gradual manner. For example, if the temperature T of the rod  23  is equal to or greater than a predetermined temperature T 1  or T 2 , the temperature T of the rod  23  can be reduced to the set temperature by increasing the speed of the cooling fan and reducing power to the ice ejecting heater  25 . On the other hand, if the temperature T of the  23  is below the predetermined temperature T 1  or T 2 , the temperature T of the rod  23  can be increased to the predetermined temperature T 1  or T 2  by reducing the speed of the cooling fan and increasing power to the ice ejecting heater  25 . 
       FIG. 11  is a graph depicting the temperature of a rod when a method of controlling an ice making assembly is performed according to an embodiment. 
     Referring to  FIG. 11 , according to the controlling methods of the first to third exemplary embodiments, the temperature of the rod  23  may vary as shown in the graph of  FIG. 11 . In the above-described embodiments, the temperature of the rod  23  may be reduced in two steps; however, the temperature of the rod  23  may be reduced in three or more steps. 
     As shown in  FIG. 11 , the temperature of the rod  23  varies slightly around the first temperature T 1  for the first set time t 1 . That is, the average temperature of the rod  23  is kept at approximately at the first temperature T 1 . After the first set time period t 1  has passed, the temperature of the rod  23  is kept at approximately the second set temperature T 2  for the second set time period t 2  until ice making is completed. 
     According to the above-described controlling method, water supplied to the tray  21  may be kept at a relatively high temperature during the early stage of an ice making operation so as to allow air contained in the water to escape before the water freezes. Thereafter, the temperature of the rod  23  is reduced to increase the ice forming rate. Accordingly, the generation of opaque ice resulting from a rapid drop in water temperature can be minimized. 
     Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments could be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings, and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.