Abstract:
The icemaker presented here may use a microcontroller, and solid state refrigeration and heat transfer elements to create ice cube qualities ranging from “clear ice” to “fast ice” in a smooth, user selectable continuum. In one embodiment, this may be accomplished by fitting a standard, high production volume icemaker mold with (1) thermoelectric coolers operated in a controlled fashion to heat or cool the mold, (2) a mold temperature sensor (such as a thermistor), and (3) a microcontroller to monitor the process and to adjust the growth rate of ice forming in the mold by adjusting heat transfer rates to optimize particular cooling phases.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   The benefit of the filing date of U.S. Provisional Application No. 60/439,620, filed Jan. 14, 2003, and entitled “Variable Rate and Clarity Icemaking Apparatus”, is hereby claimed, and the specification thereof is incorporated herein in its entirety by this reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention generally relates to an automatic icemaker, and more specifically to an improved icemaker for creating ice cubes in a user selectable continuum of qualities which may be judged to be between either “fast” in freezing rate or “clear” in appearance, or some combination thereof. 
   2. Description of the Related Art 
   The typical icemaker found in the kitchen refrigerator is located in the freezer section of the appliance. In its simplest form, water is introduced into a mold, frozen, and then harvested into a container positioned beneath the mold. In more complicated systems, ice is made in a mold, harvested into a bucket, transported to a delivery or exit port using a motorized auger, crushed or left intact, and delivered on demand to a drinking vessel or other container held by the user. 
   Ice making can be regarded as a three part process. In the first part of the process, sensible heat is removed from water which has been directed into the mold, until the water is nearly at its freezing temperature of 32° F. The term “sensible heat” has the same meaning as “enthalpy”; namely the heat absorbed or transmitted by a substance during a change of temperature which is not accompanied by a change of state. 
   The second part is the ice making process, additional heat (usually called the latent heat of fusion—144 BTU/lb) is removed from the water as it changes state from 32° F. water to 32° F. ice. In the third part of the process, the remaining sensible heat is removed and the 32° F. ice is further cooled to harvest temperature (often below 32° F. to perhaps as low as 0° F.) for delivery to the awaiting ice bin, bucket or suitable container. 
   To reduce the time it takes to freeze water to ice which can be harvested, refrigeration engineers incorporate design features in the ice making system that direct the highest volume of the coldest air (available in the freezer section of the kitchen refrigerator) into the icemaker cube mold area. Water in the ice cube mold is frozen as quickly as possible, harvested to the bucket or container, and the mold automatically refilled with water. This sequence of freeze-harvest-refill events results in the most “pounds per hour” of ice possible; however, rapid freezing directly contributes to the creation of cloudy ice. 
   Cloudy ice forms for a number of reasons, but perhaps the most significant is because impurities in the source water are entrained in the rapidly freezing ice-front present in the cube. This is because the typical water freezing rate exceeds the diffusion rate of the impurities in the water (typically dissolved gases such as nitrogen or carbon dioxide) and the freeze front direction is not well controlled. 
   In-line carbon block water filters typically supplied with automatic icemakers remove particulates and improve taste and odor of water caused by chlorine. However, these filters are not capable of removing significant amounts of dissolved gas, nor are fluid metering systems able to control the amount of gas re-dissolved into the mold water during the simple act of refilling. 
   Slow freezing usually creates clear ice, but typically available water spray or freezing tube clear ice systems are available only as commercial icemakers and are not suitable for general residential home use due to higher initial costs, higher installation costs and higher maintenance costs. Perhaps more importantly, there is a consumer need for ice which meets the occasion of its use—if ice for a portable picnic cooler is needed, the clearest possible ice is usually not necessary—nor is the cloudy, fast ice acceptable for a scheduled evening cocktail party. 
   To create ice cubes of a quality that better meets consumer requirements, the most important part of the ice making system needing improvement is the mold and associated design elements—referred to from this point on as the icemaker. Once ice is created that meets the quality expectations of the consumer, ice cube storage and ice cube delivery can be addressed in a number of ways. 
   BRIEF SUMMARY OF THE INVENTION 
   The icemaker presented here may use a microcontroller, and solid state refrigeration and heat transfer elements to create ice cube qualities ranging from “clear ice” to “fast ice” in a smooth, user selectable continuum. In one embodiment, this may be accomplished by fitting a standard, high production volume icemaker mold with (1) thermoelectric coolers operated in a controlled fashion to heat or cool the mold, (2) a mold temperature sensor (such as a thermistor), and (3) a microcontroller to monitor the process and to adjust the growth rate of ice forming in the mold by adjusting heat transfer rates to optimize particular cooling phases. 
   One important feature of the invention is that the sensible heat removal portions of ice cube making at the beginning and end of the process are accelerated with no impact on clarity of the cube, and the latent heat removal portion of the ice making process is accurately controlled to grow the clearest ice possible. 
   Using the design elements indicated above, heat is rapidly removed from water metered into the mold by a combination of convective heat transfer from available low temperature freezer air and conductive heat transfer from thermoelectric coolers directly attached to the mold. Once the water is at freezing temperature, the thermoelectric coolers are changed from cooling to heating mode to slow the freezing process, control the direction of ice front growth and create clear ice. After all the water in the mold is frozen, the thermoelectric coolers are changed from heating to cooling mode to further remove sensible heat from the ice until harvest temperature is achieved. Finally, the thermoelectric coolers are changed from cooling to heating mode to warm the mold, melt the ice-water interface and allow the cube to be slipped out of the mold on the low friction water present at the ice/mold interface. The water temperature is monitored using a temperature sensor attached to the mold, and the cooling, freezing, sub-cooling and harvest activity is initiated, controlled and terminated using the on-board microcontroller. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1 . shows front and perspective views of the freezer section of a side by side refrigerator and an undercounter refrigerator containing the icemaker. 
       FIG. 2 . is a part schematic side elevational view of a typical icemaker. 
       FIG. 3 . is a part schematic side elevational view of subject icemaker invention. 
       FIG. 4 . is a representative graph of the time/temperature relationship of the prior art icemaking process. 
       FIG. 5 . is a representative graph of the time/temperature relationship of the subject icemaker invention icemaking process. 
       FIG. 6 . is a flow chart of the overall icemaking process. 
       FIG. 6A  is a flow chart of the fill process. 
       FIG. 6B  is a flow chart of the inlet water cooling process. 
       FIG. 6C  is a flow chart of the clear icemaking process. 
       FIG. 6D  is a flow chart of the ice cube sub-cooling process. 
       FIG. 6E  is a flow chart of the harvest process. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a standard icemaker  102  located in a standard freezer section  101  of a refrigerator  100 . Ice bin  103  positioned under icemaker  102  is provided to receive harvested ice. In different embodiments, the icemaker may be installed in but not limited to the freezer section of a side by side refrigerator or bottom mount refrigerator (a refrigerator with freezer section located in the drawer). It is contemplated that the present invention may also be practiced in other types of refrigerators, such as undercounter refrigerator  104  as well as icemaking machines. A further unique application of the invention is that it may be installed in the “fresh food” or “refrigerated” section of a refrigerator. 
     FIG. 2  is a schematic elevational cross section of a typical prior art icemaker. Metal mold  201  is provided for holding water  206  and creating the shape of the ice cube. A time-metered amount of water is introduced into mold  201  and the liquid flows through channels located between individual cubes to establish a uniform level. In the presence of freezer air, the water is quickly cooled to freezing temperature, then to ice temperature and further sub-cooled to harvest temperature. Thermal snap switch  202  is provided to detect the temperature of the mold. When harvest temperature is reached, thermal snap switch  202  closes and applies electric power to harvest motor  203  located in drive housing  204  and heater  205  positioned in thermal contact with the mold. Heater  205  raises the temperature of the mold sufficiently to melt the ice/mold interface, and simultaneously, harvest motor  203  turns harvest arm  207  which slowly scoops out the ice cubes. The cubes slide out of the mold and fall into an awaiting bucket or container. Harvest arm  207  continues to rotate to an idle position, where timer cams operate a microswitch allowing a water valve to be opened and at a preset later time closed. This cam meters an amount of water to be introduced into mold  201 . The combined residual heat of the recently harvested mold and newly introduced water is sufficient to reset the mold thermal snap switch  202 . Electric power is removed from harvest motor  203  when an additional microswitch encounters the motorized cam and de-energizes the motor. 
     FIG. 3  is a schematic elevational cross section of the subject invention icemaker. The icemaker has a metal mold  301  for holding water and shaping the ice cubes. One or more heat transfer devices, such as thermoelectric coolers  302 , are attached in thermal contact to mold  301 . The other side of the cooler  302  is in thermal contact to finned heat sink  303  or other suitable heat sinking surface. A microcontroller located on printed circuit board  304  in drive housing  305  executes the process control program. A power supply  306  (such as a DC power supply) located in drive housing  305  operates the microcontroller as well as the thermoelectric coolers  302 . Harvest motor  307  may be operated from standard 120 VAC line voltage or from DC available from the power supply  306 . The water fill valve may also be operated from 120 VAC line voltage or from DC. A harvest arm  308  is fixed to harvest motor  307  for scooping out the ice cubes during the harvest cycle. A mold temperature sensor  309  may be a thermistor and detects the temperature of mold  301  during the fill, freeze and harvest periods of the process. 
     FIG. 4  is a typical graph of the temperature vs. time relationship of the prior art ice cube making process (such as used in the prior art device of  FIG. 2 ). At the beginning of the process, water is introduced into the mold at a temperature generally above the freezing point of water but typically ranging in temperature from 70° F. to 38° F. Heat is removed from the water present in the mold by convective heat transfer with the cold air present in the vicinity of the mold. During this sensible heat removal portion of the cycle, a 1° F. change in temperature results from 1 BTU of heat being removed from 1 pound of water. This temperature change is shown as segment  401 . The time to accomplish this sensible heat removal is labeled t w1 . 
   Once the water reaches the temperature of 32° F., the process continues, governed by the latent heat of fusion required to transform water to ice—144 BTU/pound. The temperature of the water remains at 32° F. until it becomes 32° F. ice at time t f1 . This segment of the process is labeled  402 . From that point onward, sensible heat continues to be removed from the now water turned ice, and the cubes are sub-cooled at a rate depicted in segment  403  until the harvest temperature is attained at time t s1 . 
     FIG. 5  is a typical graph of the temperature vs. time relationship of the subject invention icemaker depicted in  FIG. 3 . As in the prior art, at the beginning of the process water is introduced into the mold at a temperature generally above the freezing point of water but typically ranging in temperature from 70° F. to 38° F. Sensible heat is removed from the water present in the mold by a combination of convective heat transfer with the cold air present in the vicinity of the mold and conductive heat transfer resulting from the heat pump effect of the thermoelectric coolers  302 . The result is a rapid cool down  501  to freezing temperature (t w2 ), wherein t w2  is substantially smaller than the t w1  of the prior art ( FIG. 4 ). 
   This time reduction occurs because the conductive heat transfer rate of the subject invention is much higher than the convective heat transfer rate of prior art. Furthermore, in this mode of operation, the thermoelectric coolers  302  create a mold interface temperature as low as −40° F. Since the heat transfer rate is directly related to the product of the heat transfer coefficient and the temperature difference present between the heat source and sink, the rate is significantly increased over the prior art rate resulting from 0° F. to 5° F. temperatures being present in the freezer section of appliances. 
   During the latent heat of fusion removal portion of the ice making process  502 , the time to make ice depends directly on the heat removal rate. If the heat removal rate is low, ice grows slowly. Similarly, if the heat removal rate is high, ice grows quickly. Since typical freezer sections of refrigerators in which the subject invention icemaker is operated create conditions for high heat removal, ice grows quickly unless heat is reintroduced into the mold. The t f2  of the subject invention icemaker (time to freeze) may be shorter if the thermoelectric coolers  302  are operated to pump heat at a higher rate than possible in prior art designs, or longer than t f1  of prior art icemaker designs if the thermoelectric coolers are operated in a reverse polarity to supply heat to the mold. Fast ice or clear ice is made by controlling this heat transfer rate. 
   Finally, the time to harvest t s2  as the ice cube is sub-cooled  503  below 32° F. is shorter in the subject invention icemaker ( FIG. 3 ) than in the prior art ( FIG. 2 ). To accomplish this, the thermoelectric coolers  302  are set to remove heat by conductive heat transfer from the mold at a rate substantially higher than present in convective heat transfer of prior art icemakers. 
   The result of this configuration of elements is an icemaker which exhibits variable icemaking rate (pounds/hour) as well as cube clarity, resulting from the speed with which 32° F. water is transformed into 32° F. ice. 
     FIG. 6  is a flow chart of the general ice making process executed by the microcontroller  304  present in the subject invention icemaker. In  601 , the mold is filled with water. The status of a human interface device  310  such as potentiometer, slide switch, keyboard input, touch screen, etc. (but not limited to these human interface devices) is obtained in  602  to indicate to the microcontroller  304  if the user desires clear ice, fast ice or a quality of ice in between those two endpoints. This status is may be, in one embodiment, a numeric representation (typically ranging from −100 to +100 or −127 to +127 or 0 to 255), of the angular or linear position of human interface device  310  (in the case of a potentiometer), or a numeric representation formed from combining successive keypad entries. 
   Of course, human interface device  310  may take many forms, and the above are simply examples. Furthermore, the range of travel of the human interface device  310  may be interpreted as containing user selections ranging from clear ice, fast ice or a quality of ice in-between, but not limited to those two points. 
   Once the user input has been read by microcontroller present on printed circuit board  304 , the value determines the quantity of heat applied to mold  301  to slow the freeze process and create clear ice, or the quantity of heat to be removed from mold  301  to accelerate the freeze process and create fast ice. 
   In the case when user input device  310  creates an ice quality request ranging from −100 to 100, settings in the range −100 to 0 may in one embodiment be considered to be the duty cycle of DC power from power supply  306  applied to thermoelectric coolers  302  to create clear ice by heating mold  301 . For example, if the total time period of the duty cycle is considered to be 10 minutes, the −100 value may correspond to DC power continuously applied to thermoelectric cooler  302  in a heating mode; a −50 value may correspond to DC power applied for 5 minutes followed by an off time period of 5 minutes; a −30 value may correspond to DC power applied for 3 minutes followed by an off time period of 7 minutes, and so on. 
   Similarly, settings in the range 0 to +100 may be considered to be the duty cycle of DC power applied to thermoelectric cooler  302  to create fast ice by setting the appropriate polarity of DC voltage applied to the thermoelectric coolers to conductively cool mold  301 , perhaps in combination with convection cooling available from the ambient available in the kitchen appliance containing the subject invention icemaker. For example, if the time period of the duty cycle is considered to be 10 minutes, the 0 value may correspond to DC power continuously applied to thermoelectric cooler  302  in a cooling mode for 0 minutes followed by an off time period of 10 minutes; a  30  value may correspond to DC power applied continuously for 3 minutes followed by an off time period of 7 minutes; a 70 value may correspond to DC power applied for 7 minutes followed by an off time period of 3 minutes, and so on. 
   Again, and as will be appreciated by one of ordinary skill in the art, the above values and duty cycles are simply representative examples, and should not be considered limiting. A wide variety of other values and duty cycles may be used as well. 
   In  603 , the desired quality of ice is created by controlling the heat transfer rate during the state change process using the thermoelectric coolers  302  as heat sources or heat sinks for the icemaker mold  301 . In  604 , the mold temperature sensor  309  detects the temperature of the material present in the mold  301 . If the ice is not frozen, in branch  606  the human interface device  310  is queried in  602  for new or unchanged requirements and the heat transfer process in  603  is either left unchanged or modified. In  604 , if the ice is frozen, a harvest process  605  is executed. After the completion of the harvest process  605 , the flow of control passes back to the fill process of  601 . The process depicted in  FIG. 6  is merely illustrative of one embodiment of a process for making ice according to the teachings of the present invention. 
     FIG. 6A  describes the fill process, in one embodiment. In  610 , an internal variable, called the water fill timer, and representing water valve open time, is set to a value of 0. After that occurs, the water valve is opened as indicated in  611 . A decision is made in  612  based on the value of the water fill timer which is periodically incremented by the microcontroller  304 , and is representative of the real elapsed time of the process. If the water fill timer is smaller in magnitude than a preset variable called fill time (branch  614 ), the water valve remains open ( 611 ). If the water fill timer is greater in magnitude than the preset fill time, the water valve closes as in  613  and flow of control passes onward to the freeze process ( FIG. 6B ). 
     FIG. 6B  schematically describes the inlet water cooling process. In  621 , the microcontroller  304  sets the polarity of the DC voltage available from power supply  306  applied to thermoelectric coolers  302  to cause maximum heat extraction from the icemaker mold  301 . In  622 , the temperature of the mold  301  is measured using mold temperature sensor  309 . In  622 A, if the actual temperature is greater than or equal to 33° F., thermoelectric coolers  302  will continue cooling and the mold  301  temperature will be periodically re-measured as depicted in branch  623 . If the actual temperature is less than 33° F., the inlet water cooling process is complete and flow of control passes onward to the clear icemaking process shown in  FIG. 6C . 
     FIG. 6C  is a flow chart showing the activity and decisions made by the microcontroller located on printed circuit board  304  to create the quality and rate of ice requested by the user. In  631  the position of a human interface device  310  such as a potentiometer or keyboard keystroke is detected and translated into an internal variable representative of the heat removal rate required to achieve the user input request. The thermoelectric cooler  302  heat removal rate is set to the user requested level in process block  632 . 
   In one extreme setting of the input potentiometer  310 , the thermoelectric coolers  302  are operated as cooling devices. In the other extreme setting of the input potentiometer  310 , the thermoelectric cooler duty cycle is adjusted to maintain the mold  301  temperature slightly below the freezing temperature of water—as either heat source or heat sink. The temperature of the mold  301  is measured in process block  633 . In  634 , a decision is made to continue the ice growth process at the user selected rate (branch  636 ) or terminate the process if the mold temperature is less than 32° F. When ice making is complete  635 , flow of control moves onward to the sub-cooling process ( FIG. 6D ). 
   The flow chart of  FIG. 6D  depicts the activity required to further remove heat from the ice to achieve a suitable harvest temperature. In  641 , the microcontroller  304  sets the DC power applied to the thermoelectric coolers  302  to achieve maximum cooling of the mold  301 . In  642 , the temperature of the mold  301  is determined by measuring a physical quality such as electrical resistance, of the calibrated mold sensor  309 . In the decision block of  643 , if the mold temperature is less than the harvest temperature (a value typically between 0° F. and 32° F.), the process is terminated. Otherwise, in branch  644  the thermoelectric coolers  302  continue to be operated at maximum cooling potential. When the ice reaches the harvest temperature, the process is terminated and flow of control moves onward to the harvest process shown in  FIG. 6E . 
   Entered on completion of the sub-cooling process, activity in  FIG. 6E  describes the harvest of ice from the mold. In  651  the harvest motor  307  is energized. This causes the harvest arm  308  to rotate to directly contact and apply force to the ice frozen in the mold  301 . The harvest arm  308  is connected to harvest motor  307  through a slip clutch, thereby allowing the motor  307  to operate without damage until the ice is ejected from the mold  301 . In  652 , the polarity of DC voltage applied to the thermoelectric coolers  302  causes the reversal of the cold and hot side. At this maximum heat mode, heat is extracted from the refrigerator ambient through heat sink  303  and the mold  301  is warmed. Once enough heat has been applied to the mold  301 , the ice/mold interface melts and the cubes slip under force of the rotating harvest arm  308 . When all the cubes have been ejected from the mold  301 , harvest arm  308  continues to rotate to a rest position where a suitably located microswitch detects the position in  653 , and transmits a signal to the microcontroller  304  which turns off harvest motor  307 . 
   At the end of  654  in  FIG. 6E , the ice making process is complete and typically restarts with a fill process as shown in  FIG. 6A . 
   What has been described above is an embodiment of the novel aspects of the present invention. One of ordinary skill in the art will recognize that various modifications may be made to the implementation of the present invention, both in the physical components as well as the processes it performs, without departing from the scope and spirit of the claims below.