Refrigeration – Automatic control – By congealed removable product condition
Reexamination Certificate
2000-08-17
2001-11-06
Walberg, Teresa (Department: 3742)
Refrigeration
Automatic control
By congealed removable product condition
C073S170260
Reexamination Certificate
active
06311503
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to automatic ice makers, and more particularly to detecting ice readiness in a belt ice maker which contains water during formation of ice cubes and from which the formed ice cubes are later released.
Refrigerator ice makers typically form ice cubes in the freezer compartment and release the formed ice cubes through a dispenser located in a freezer compartment door. Refrigerator ice makers of the elastomer belt type include an elastomer belt, or mold, having a plurality of cube compartments. Water freezes in the cube compartments to form ice cubes, and the fully frozen cubes are discharged, or released, from the cube compartments into a container. Belt ice makers do not require as much space as, and have a higher ice rate, (i.e., make more ice) than, many other types of ice makers.
Although belt ice makers provide the advantages mentioned above, determining whether ice is completely frozen in a belt ice maker is difficult. Specifically, a temperature measurement typically is utilized to determine whether water in a cube compartment is completely frozen and ready to be dispensed. In a belt ice maker, however, the mold moves and has a low thermal conductivity. Therefore, a thermistor, thermocouple, or other temperature sensor has to be in sliding contact with the mold, and accuracy of a temperature sensed is impacted by freezer air temperature and air velocity.
Releasing less than completely frozen ice cubes into a container in a freezer is not desirable since the unfrozen water then freezes in the container and multiple cubes may be frozen together. Also, unnecessarily maintaining fully frozen ice cubes in a mold adversely impacts the ice rate of the ice maker.
SUMMARY OF THE INVENTION
An exemplary embodiment of an ice readiness sensor for accurately sensing ice readiness in an ice maker includes a capacitance bridge circuit, or bridge, having a first impedance as a first bridge arm, a second impedance as a second bridge arm, a tunable capacitor as a third bridge arm, and a probe as a fourth bridge arm. The probe includes electrode strips that can be placed in close proximity to an ice maker belt, and develops a capacitance which depends, at least in part, on dielectric properties of contents of the ice cube compartment. The term “close proximity” as used herein means that the electrode strips are sufficiently close to air/water in the ice cube cavity so that the dielectric constant of the medium in the cavity affects the capacitance developed by the electrodes.
The first and second bridge arms are connected at a first bridge node, the first and third bridge arms are connected at a second bridge node, the second and fourth bridge arms are connected at a third bridge node, and the third and fourth bridge arms are connected at a grounded fourth bridge node. The first and fourth bridge nodes are input terminals for receiving an AC drive signal from an AC source, and the second and third bridge nodes are output terminals.
A signal processing unit coupled to the second and third bridge nodes includes an amplifier whose output is coupled to a rectifier by a coupling capacitor. In the exemplary embodiment, the amplifier is a differential amplifier which generates an output signal that varies in amplitude in direct relation to the extent by which the capacitance of the probe differs from the capacitance of the tunable capacitor. A filter capacitor is coupled to the rectifier output so that a voltage across the capacitor is proportional to the amplifier output signal amplitude. An output signal from the processing unit is supplied, for example, to a controller.
The ice readiness sensor is calibrated so that the bridge circuit is balanced when the ice cube cavity directly above the probe is empty; i.e., when such cube cavity is empty, voltage across the bridge is zero, or nearly zero. When water is in such cube cavity, the probe capacitance increases because the dielectric constant of water is 80 times that of air. As a result, the bridge becomes unbalanced and the voltage signal sensed by the amplifier increases as compared to the signal when air is in the cube cavity. As the water freezes, the dielectric constant of the water decreases to about six times that of air and therefore, as the water freezes, the imbalance of the bridge decreases as does the signal sensed by the amplifier.
The above described ice readiness sensor is particularly well suited for use with a belt ice maker since the sensor does not need to be in physical contact with ice or an ice mold. In addition, since the sensor is a capacitance sensor rather than a temperature sensor, the sensor accuracy is not impacted by freezer air temperature and air velocity. Such accuracy facilitates achieving desired ice rates as well as avoiding release of less than completely frozen ice cubes into an ice container.
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Edelstein William Alan
Shapiro Andrew Phillip
Tiemann Jerome Johnson
Breedlove Jill M.
Cabou Christian G.
Fastovsky Leonid M
General Electric Company
Walberg Teresa
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