Patent Publication Number: US-6705090-B2

Title: Ice maker harvest control and method

Description:
The present application is a continuation of application Ser. No. 09/930,420, filed Aug. 15, 2001 now U.S. Pat. No. 6,405,546 and claims benefits of Prov. No. 60/225,663 file Aug. 16, 2000. 
    
    
     FIELD OF THE INVENTION 
     The present application relates generally to ice making machines, and specifically to ice harvest controls and sensors as used therein. 
     BACKGROUND 
     Ice making machines are well known in the art, and typically include an ice cube making mechanism located within a housing along with an insulated ice retaining bin for holding a volume of ice cubes produced by the ice forming mechanism. In one type of ice maker a vertically oriented evaporator plate is used to form a slab of ice characterized by a plurality of individual cubes connected by ice bridges there between. As the slab falls from the evaporator plate into the ice bin, the ice bridges have a tendency to break forming smaller slab pieces and individual cubes. As is well understood, the ice slab is formed by the circulating of water over the cooled surface of the evaporator plate, the plate forming a part of a refrigeration system including a compressor and a condenser. 
     Of critical importance to ice makers of this general type, is knowing when the ice is of sufficient thickness to be harvested. Once the harvest point is reached, the making of ice is discontinued by stopping the flow of water over the evaporator and the cooling thereof. The evaporator plate is then heated, typically by the use of hot gas from the refrigeration system. The ice slab then melts slightly releasing its adhesion to the plate so that it can fall into the bin positioned there below. Various controls have been proposed and used over the years to signal the harvest point. One approach is to use electrical conductivity whereby an electrical probe is positioned closely adjacent the surface of the evaporator. When ice builds to a desired thickness the plate comes in contact with the flow of water causing a conductivity connection which can trigger the harvest cycle. A problem with this sensor type concerns the evaporative or electrically caused chemical deposition on the probe resulting in a weak or no signal failure condition wherein the harvest point is not detected. 
     The harvest point can also be indicated by the lost water approach. In ice makers of the above described type, a water pan is positioned below the evaporator to catch the water not immediately frozen thereon. The water is then recycled from the tray back over the evaporator. If water that freezes on the evaporator is not replenished into that water circulatory system, then the water level in the pan will gradually be lowered as the ice is formed. Thus, various techniques have been used to sense the low water level point that corresponds with a desired ice build-up or thickness. It is known to use an electromechanical float mechanism that can signal when that point is reached. However, such systems are prone to mechanical failure whereby contact with the water can lead to corrosion and fouling problems. Other sensors including photo optical sensors are used, but again are located in or closely adjacent the water pan and thereby subject to corrosive or depositional effects that can degrade the performance thereof. 
     Accordingly, it would be desirable to have an ice harvest sensing system that is significantly less likely to be damaged or subject to corrosive or depositional effects and can thereby accurately and reproducibly sense, over time, the proper harvest point. 
     SUMMARY OF THE INVENTION: 
     The present invention comprises an ice harvest system for use in an ice maker. The ice maker herein works in the conventional manner wherein a refrigeration system provides for cooling of the evaporator. Ice is formed thereon as water is pumped by a re-circulating pump to flow from a water distribution tube over the evaporator surface. Water that is not frozen thereon flows into a water pan positioned there below. A pressure fitting is positioned in the pan at the bottom thereof and connected to a pneumatic tube. The pneumatic tube is connected to a pressure sensor located on a control board at a position remote from the water pan. As water fills the pan it attempts to flow into the fitting interior. Air trapped in the fitting and in the tube is compressed slightly by this action and this pressure is communicated through the tube to the pressure transducer/sensor. The sensor then converts this pressure into a voltage reading, which is input to and converted by a microprocessor of the control board for interpretation as a pressure value. As the water level in the tray lowers, the pressure transmitted to the pressure sensor reduces. When a predetermined low pressure is sensed, a harvest point is reached and a harvest cycle is initiated. In particular, the water pump is stopped along with cooling of the evaporator. A hot gas valve is then opened to warm the evaporator resulting in the discharge of the ice there from. 
     A major advantage of the pressure sensing strategy of the present invention is the location of the pressure sensor on the control board at a point within the ice maker substantially distant from the water tray. As a result thereof, any water based degradation thereof due to sedimentation, corrosion or the like is greatly minimized, if not eliminated. The control of the present invention is also low in cost as the tube and pressure fitting are inexpensive and easily replaced and as the pressure sensor is relatively inexpensive relative to other sensor/transducer technologies. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     A better understanding of the structure, function, operation and advantages of the present invention can be had by referring to the following detailed description which refers to the following drawing figures, wherein: 
     FIG. 1 shows a perspective view of an ice maker mounted atop an ice storage bin. 
     FIG. 2 shows a partial cross-sectional view of the interior of the ice maker. 
     FIG. 3 shows a schematic representation of the ice maker. 
     FIG. 4 shows an enlarged view of the ice maker control board. 
     FIG. 5 shows an enlarged partial cross-sectional view of the water pan and pressure fitting. 
     FIGS. 6A and 6B show a flow diagram of the general control strategy of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The ice maker of the present invention is seen in FIG. 1, and referred to generally by the numeral  10 . Ice maker  10  includes an exterior housing  12  and is positioned atop an insulated ice retaining bin  14 . As is further understood by referring to FIGS. 2 and 3, and as is conventional in the art, ice maker  10  includes a vertical ice forming evaporator plate  16 , a condenser and fan  18  and a compressor  20  connected by high pressure refrigerant lines  21   a  and low pressure line  21   b . As is also well understood, the refrigeration system herein includes an expansion valve  22  and a hot gas valve  24 . A water catching pan  26  is positioned below evaporator  16  and includes a partial cover  27 . A water distribution tube  28  having a water inlet  29  extends along and above evaporator  16 . A water supply solenoid valve  30  has an inlet connected to a source of potable water, not shown, and an outlet line  31  supplying water to pan  26 . A water pump  32  provides for circulating water from outlet  32   b  thereof to inlet  29  of distribution tube  28  along a water line  34 . A solenoid operated dump valve  36  is fluidly connected to line  34  and serves, when open, to direct water pumped thereto to a drain, not shown. An evaporator curtain  37  is pivotally positioned closely adjacent evaporator  16  and includes a magnetic switch  38  for indication when it has moved away from evaporator  16  to an open position indicated by the dashed line representation thereof. For purposes of clarity of the view of FIG. 2, the various fluid connections of pump  32 , dump valve  36  and water supply valve  30  are not shown, such being represented in schematic form in FIG.  3 . 
     As particularly seen in FIG. 4, and also by referring to FIG. 2, an electronic control board  40  is located within a separate housing  41  at a position remote and physically isolated from pan  26  and evaporator  16 . Control board  40  includes a microprocessor  42  for controlling the operation of ice maker  10 . Board  40  includes a pressure sensor  44 , such as manufactured and sold by Motorola, Inc. of Phoenix, Ariz., and identified as model MPXV5004G. As understood by also viewing FIG. 5, a plastic pneumatic tube  46 , shown in dashed outline, is connected to sensor  44  and on its opposite end to a cylindrical air cup or fitting  48 . Those of skill will understand that housing  41  includes a cover, not shown, that provides for the enclosing and protection of control  40  and sensor  44  therein and through which tube  46  passes prior to connecting to sensor  44 . 
     A Fitting  48  resides in pan  26  at the bottom thereof and is press fit within a circular ridge  49  that is formed as an integral molded portion of the bottom surface of pan  26 . Fitting  48  includes an outer housing  48   a  defining an inner air trapping area  48   b  and a tube connecting portion  48   c . Four water flow openings  50  exist around a bottom perimeter of housing  48   a.    
     The operation of the present invention can be better understood by referring to the flow diagram of FIGS. 6A and 6B wherein the basic operation of the present invention is shown. At start block  51  power is provided to control  40 . At block  52  compressor  20  is turned on and substantially simultaneously at block  54  fill valve  30  and dump valve  36  are opened. Thus, cooling of evaporator  18  begins and water flows into pan  26 . At decision block  56 , once a predetermined pump-on water level is reached in pan  26 , as indicated by the level line represented by the letter P in FIG. 5, circulatory water pump  32  is turned on at block  58 . The pump-on point is sensed by sensor  44 . In particular, as water fills pan  26 , water flows through holes  50  of fitting  48 . As that occurs, air trapped in area  48   b  is slightly compressed and forced into tube  46  which communicates such pressure increase to sensor  44 . That pressure is then input as a voltage to microprocessor  42  which assigns a numerical value thereto corresponding to a pressure scale. Therefore, when the predetermined pressure value is sensed that corresponds to the pressure at level P, pump  32  is turned on. Because of the fluid connections of pump  32  and dump valve  36 , the action of pump  32  serves to move any water in pan  26  to valve  36  causing the draining away thereof. Thus, a minimum water level, indicated by the level line represented by the letter M in FIG. 5, is sensed in the same manner as described above for level P. When that predetermined volume of the water has been removed from pan  26 , pump  32  is stopped at block  62 . As the water supply valve remains on, the level in pan  26  begins to rise and when the P level is again sensed at block  64 , then at block  66 , pump  32  is re-started and fill valve  30  closed. As dump valve  34  remains open, water will again be pumped from pan  26 . At block  68  control  40  again senses for the attainment of the M level. When that occurs, then, at block  70 , water pump  32  is stopped, dump valve  34  is closed and fill valve  30  is opened. It can be appreciated that blocks  52 - 68  serve as a dump cycle whereby any contaminants that have accumulated in pan  26  are agitated by the action of pump  32  and the inflow of water and are twice flushed in this manner and removed from the system. 
     At block  72  control  40  monitors for the attainment of a maximum fill level for pan  26  indicated by the level line denoted by letters MX. When this highest pressure level is sensed, then at block  74  fill valve  30  is closed. At block  76 , a 45 second clock is initiated to provide for some pre-cooling of the water delivered to pan  26  through flow over evaporator  16 . At block  78  pump  32  is again turned on. A further 45 second clock is set at block  80 , and when that has timed out, fill valve  30  is opened. It will be understood by those of skill that action of pump  32  will serve to fill fluid line  34  and distribution tube  28  which will slightly lower the level of water in pan  26  below that of the desired maximum water volume indicated by level MX. Thus, fill valve  30  is opened at block  82 , to replenish that volume as is determined at block  84 . At block  86 , fill valve  30  is closed when the desired starting maximum level MX is again attained. 
     At this point pump  32  is operating to flow water over evaporator  16  as such is being cooled by the action of compressor  20 , condenser and fan  18  and expansion valve  22 , all as operated by control  40 . As ice forms on evaporator  16 , the water level in pan  26  goes down as does the pressure sensed by sensor  44 . When a predetermined harvest water level is reached, as indicated by the level line denoted H, a corresponding predetermined pressure value is sensed by control  40  at block  88 . When the harvest point is indicated, pump  32  is stopped and hot gas valve  24  is opened at block  90 , causing evaporator  16  to warm resulting in the release of the ice slab formed thereon. Of course, those of skill will understand that other heating means known in the art could be employed, such as, an electrical heater integral with the ice forming evaporator. As is well understood, when the slab of ice falls from evaporator  16 , curtain  37  is opened and switch  38  is closed, signalling to the control  40  the release of the ice slab from evaporator  16 . As is also known, to insure that the slab of ice has fallen into bin  12  and is no longer in the vicinity of evaporator  16 , at block  96 , the control herein awaits the remaking of switch  38  which occurs when curtain  36  is free to swing back to its normal closed position unobstructed by any ice. At block  98  the control returns to start and initiates a further ice making cycle. 
     It was found that the pressure-based water level sensing as described herein provides for very accurate and repeatable determination and control thereof, and hence, for very reliable control of the harvest cycle of an ice maker. In particular, the physical isolation of the pressure sensor  44  from pan  26  contributes to this improved performance by serving to prevent any degradation of the sensor due to the presence of water and/or the corrosive impact thereof.