WO2006088887A2

WO2006088887A2 - Capacitive rain sensor

Info

Publication number: WO2006088887A2
Application number: PCT/US2006/005213
Authority: WO
Inventors: P. Edward Clugston, Jr.
Original assignee: Control Devices, Inc.
Priority date: 2005-02-15
Filing date: 2006-02-15
Publication date: 2006-08-24
Also published as: EP1856459A2; WO2006088891A2; WO2006088887A3; KR20070103067A; WO2006088891A3; US20080250796A1; JP2008530497A

Abstract

Methods and apparatus for making and sensing a liquid substance such as liquid water. Also, apparatus and methods for sensing the change of phase of a substance. In one embodiment, a fringe-effect capacitor is placed proximate to a surface for which it is desirable to sense the presence of liquid water, such as a windshield. The presence of rain on the surface of the windshield changes the electrical flux between electrodes of the capacitor. This change is sensed, and used for other purposes, such as turning on windshield wipers. Also, apparatus and methods for a fringe-effect capacitor.

Description

CAPACITIVE RAIN SENSOR

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application Serial Nos. 60/653,194, filed February 15, 2005; and 60/742,730, filed December 6, 2005, both of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention pertains to improvements in capacitive sensors, including sensors used for detection of rain or other liquids; and also pertains to improvements in fringe-effect capacitors.

BACKGROUND OF THE INVENTION Detecting rain on an automotive windshield is a complex task due to the'number and types of variable conditions encountered. The result of rain interacting with the surface of a windshield is a very dynamic situation, if considered on the relatively small scale of rain droplets.

The characteristics of rain droplets cover a significant range of size or volume. Also, the accumulation rate can vary independently of the droplet size. Even within a given environmental condition, the droplets impacting the windshield are not the same size since some have increased there total volume as the result of being combined during mid-air collisions.

The vehicle speed will of course influence the impact splatter pattern of the incoming droplet. The droplet size, droplet speed, vehicle speed, and the rate of accumulation can all influence the instantaneous pattern on the windshield. The rate of accumulation is a factor due to the proximity of other droplets that have previously impacted the windshield or those incoming droplets that are close enough to the windshield to be hit by the back splash of the impacting droplet. The initial altitude where the droplet formed and the final size will govern its terminal velocity. Both the air humidity and vehicle speed play a role in droplet evaporation. The most profound effect occurs in the presence of slowly accumulating light mist conditions, since the actual volume of the droplets is small, thus making even moderate evaporation a more significant influence. The evaporation from any size droplet will result in an evaporative cooling of the windshield, thus lowering the windshield temperature.

The conditions of the wiper blades can greatly influence how effectively the windshield is cleared following the wipe event. This will establish the "cleanest condition" that can be achieved at any given time.

Accurately detecting and reporting the temporally dynamic conditions of rain on an automotive windshield under the varying conditions of both the environment and the vehicle is not a trivial challenge.

What is needed is a sensor which provides a response to the presence of a liquid. Also, there is a need for improved fringe-effect capacitors. Some embodiments of the present invention address one or both of these problems in novel and inventive ways.

SUMMARY OF THE INVENTION

A further embodiment of the present invention pertains to a capacitor. The embodiment includes a first electrode mounted on a surface of substrate, the first electrode having a first extending finger having a variable width. The embodiment also includes a second electrode mounted on the surface having a second finger extending along side the first finger, the second finger being spaced apart from the first finger by a variable gap. One embodiment of the present invention pertains to a capacitor for sensing capacitance near a surface. The embodiment includes a first electrode mounted on the surface. The embodiment also includes a first electrode having a first plurality of substantially planar fingers extending on the surface in a first direction, at least a portion of each of the first fingers having a varying width which increases along the first direction. The embodiment further includes a second electrode mounted on the surface, the second electrode having a second plurality of substantially planar second finger extending on the surface in a second direction generally opposite to the first direction, at least a portion of each of the second fingers having a varying width which increases in the first direction, each of the second fingers being interdigitated with different ones of the first fingers and spaced apart therefrom by a gap.

Another embodiment of the present invention pertains to a capacitor responsive to a change in dielectric proximate to a surface. The embodiment includes a first electrode mounted on the surface and extending on the surface in a first direction, the first electrode having a first varying width which monotonically increases along the first direction. The embodiment further includes a second electrode mounted on the surface adjacent to the first electrode, the second electrode having a second varying width which monotonically increases in the first direction, the second electrode being spaced apart from the first electrode by a gap which increases along the first direction.

Another embodiment of the present invention pertains to a fringe-effect capacitor. The embodiment includes an insulating substrate having first and second opposing sides and first and second opposing surfaces. The embodiment further includes a first electrode mounted on the first surface proximate the first side, the first electrode having a first finger with a first length and extending toward the second side. The embodiment further includes the first finger having a first variable width; and a second electrode mounted on the first surface proximate the second side, the second electrode having a second finger with a second length extending toward the first side, the second finger having a second width, the second finger being spaced apart from the first finger by a variable gap wherein the relationship between the first variable width and the variable gap is such that portions of the first finger widen along a direction along the first length, and the gap from the portion of the first finger to the second finger widens along the same direction.

A further embodiment of the present invention pertains to a sensor for measuring the presence of a liquid. The embodiment includes a fringe-effect capacitor having a first electrode and a second electrode separated by -a variable gap, one of the first electrode or second electrode having a variable width, the variable gap between the first and second electrodes increasing as the variable width increases; and an electrical circuit which includes a reference capacitor having an input electrode and an output electrode, a source of oscillating voltage, and at least 4 diodes arranged in a four arm bridge, one of the first electrode or second electrode and the input of the reference capacitor receiving an input from said source, and the other of the first electrode or second electrode and the output of the reference capacitor being provided to opposing arms of the bridge.

It will be appreciated that the various apparatus and methods described in this summary section, as well as elsewhere in this application, can be expressed as a large number of different combinations and subcombinations. AU such useful, novel, and inventive combinations and subcombinations are contemplated herein, it being recognized that the explicit expression of each of these myriad combinations and subcombinations is excessive and unnecessary.

These and other features and aspects of different embodiments of the present invention will be apparent from the claims, specification, and drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top, planar view of a capacitive sensor according to one embodiment of the present invention.

FIG. 2 is a graph depicting the width of an electrode verses the distance from the sensor centerline for the apparatus of FIG. 1.

FIG. 3 is a graph depicting the gap of an electrode verses the distance from the sensor centerline for the apparatus of FIG. 1.

FIG. 4 is a graph depicting the gap of an electrode verses the electrode width from the sensor centerline for the apparatus of FIG. 1. FIG. 5 is a graph showing capacitance and temperature as a function of time for the apparatus of FIG. 1.

FIG. 6 is a graph showing capacitance as a function of temperature for the apparatus of FIG. 1.

FIG. 7 is a schematic representation of an icemaker according to one embodiment of the present invention.

FIG. 8 is a schematic representation of an icemaker according to another embodiment of the present invention.

FIG. 9 is a schematic representation of an icemaker according to another embodiment of the present invention. FIG. 10 is a top, planar view of a sensor according to another embodiment of the present invention.

FIG. 11 is a top, planar view of a sensor according to another embodiment of the present invention.

FIG. 12 is a top, planar view of a sensor according to another embodiment of the present invention.

FIG. 13A is a side elevational view of an ice container according to one embodiment of the present invention.

FIG. 13B is an end elevational view of the apparatus of FIG. 13 A.

FIG. 14A is a side elevational view of an ice container according to another embodiment of the present invention.

FIG. 14B is an end elevational view of the apparatus of FIG. 14A. FIG. 15 A is a schematic representation showing fringing electrical flux between a pair of surface conductors on a dry surface.

FIG. 15B is a schematic representation showing fringing electrical flux between a pair of surface conductors in contact with a thin layer of ice. FIG. 15C is a schematic representation showing fringing electrical flux between a pair of surface conductors in contact with a thick layer of ice.

FIG. 16 is a prior art configuration showing a top view of three electrical conductors arranged on an insulating surface and exhibiting fringe-effect capacitance.

FIG. 17 shows graphically the relationship of capacitance ratio to ice thickness for the apparatus of FIG. 16.

FIG. 18 A shows graphically the capacitance of a quantity of ice in contact with a fringe-effect capacitor according to one embodiment of the present invention as a function of time and temperature.

FIG. 18B is a graphical representation of the process of FIG. 18A showing the capacitance of the quantity of water as a function of its temperature.

FIG. 19 is a top plan view of a fringe-effect capacitor according to another embodiment of the present invention.

FIG. 20 is a schematic representation of pairs of electrodes for illustrating the effect of non-adjacent electrodes for sensing the phase change of a substance in contact with the electrodes.

FIGS. 21 A is a top planar view of a packaged frost sensor according to one embodiment of the present invention.

FIGS. 21B is a side elevational view of the sensor of FIG. 21 A.

FIGS. 21C is a bottom plan view of the sensor of FIG. 21 A. FIG. 22 shows an ice maker according to another embodiment of the present invention as photographed from the top.

FIG 23A is a side view of an ice cube.

FIG. 23B is a top view of the ice cube of FIG. 23A.

FIG. 24 is a schematic representation of a portion of the apparatus of FIG. 22. FIG. 25 is an ice maker according to another embodiment of the present invention as shown from the top. FIG. 26 is an ice maker according to another embodiment of the present invention as shown from the top.

FIG. 27 is an ice maker according to another embodiment of the present invention as photographed from the top. FIG. 28 is an ice maker according to another embodiment of the present invention as shown from the top.

FIG. 29 is a graph which relates the normalized capacitance of water as a function of the liquid or solid state of the water.

FIG. 30 is a graph which relates radial wall thickness of an ice cube to the weight of the cube.

FIG. 31 is a graphical representation of the capacitance of different ice sensors as a function of time.

FIG. 32 is a perspective view of a portion of an ice maker according to one embodiment of the present invention. FIG. 33 is a schematic representation of a circuit according to one embodiment of the present invention.

FIG. 34 is a perspective view drawn in part from a photograph of one example of an evaporator according to one embodiment of the present invention.

FIG. 35 is a top plan view of a fringe-effect capacitor according to another embodiment of the present invention.

FIG. 36 is a top plan view of a fringe-effect capacitor according to another embodiment of the present invention.

FIG. 37 is a perspective view of a windshield incorporating a sensor according to one embodiment of the present invention. FIG. 38 is an enlarged cross sectional view of the windshield of FIG. 37 in the vicinity of the sensor. DESCRIPTION OF THE PREFERRED EMBODIMENT For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

This application incorporates by reference U.S. Patent Application Serial Number 10/898,842, filed 7/26/04, entitled TAMPER EVIDENT CONNECTOR FOR AN ENGINE RADIATOR; U.S. Patent No. 6,311,503, issued November 6, 2001; U.S. Patent No. 6,438,976, issued August 27, 2002; U.S. Patent No. 4,766,369, issued August 23, 1988; U.S. Patent No. 6,239,601, issued May 29, 2001; and the article Fractal Capacitors, IEEE Journal of Sold State Circuits, vol. 33, no. 12, December, 1998. Also incorporated herein by reference is U.S. Patent No. 6,842,018, issued January 11, 2005, to Mclntosh. Also incorporated herein by reference is a patent application filed by the same Applicant on 15 February 2006, Attorney Docket No. 31142-37, entitled METHODS AND APPARATUS FOR DETECTING AND MAKING ICE.

Some embodiments of the present invention pertain to measuring the progress of ice formation during the transition from a fully liquid state to a partially frozen or completely frozen ice cube. In some embodiments, this measurement can be used to increase the rate of production of ice. In such embodiments the ice cube can be ejected even though the center of the cube is not frozen and is instead still liquid. A partially frozen ice cube can be ejected and maintain its structural integrity if the wall is sufficiently thick. By placing the partially frozen cube into a bin that is at a temperature below freezing, the solidification process continues to completion within the bin. However, while solidification of the first cube progresses, the liquid container can be recycled to the beginning of the process, and refilled with liquid water to begin formation of a second cube. In such embodiments, the time required to freeze the first and second set of cubes can be overlapped, thus increasing the overall rate of ice cube production.

Some embodiments of the present invention include a method of sensing the formation of ice using a capacitive technique, preferably with the sensor electrodes being located near the water sample. Preferably, the water sample is located close enough to the electrodes that the dielectric constant of the water affects the capacitance of the sensor. It is known that the dielectric constant of liquid water is about 80, whereas the dielectric constant of ice is about 3. In some embodiments of the present invention, the sensor is adapted and configured to change capacitance in response to varying quantities of liquid water and varying thicknesses of ice proximate the sensor electrodes. This factor of 26 change in capacitance can be measured in a number of ways, including a four arm bridge circuit

In some embodiments, the principle of operation of the capacitor corresponds to that of a lateral flux capacitor, or fringe-effect capacitor. In some embodiments, the electrodes are arranged laterally to each other on a substrate (for example, as shown in U.S. Patent No. 4,766,369), in contrast to parallel plate-type capacitors.

As noted in U.S. Patent No. 4,766,369 and U.S. Patent No. 6,239,601, smaller electrode widths and smaller electrode gaps can be used to detect relatively thin layers of ice. Further, larger electrodes with larger gaps can be used to detect thicker layers of ice. A smaller pattern responds rapidly to thin layers of ice, but the pattern reaches a point where increasing thickness does not provide any significant change in the output. With regards to the larger pattern, it responds less to smaller thicknesses of ice, yet is capable of responding to thicker layers which are no longer detectable by the small pattern. It follows then that intermediate electrode widths separated by intermediate gaps would respond to moderate thickness layers of ice. Although the electrode width and spacings can be varied discretely, it is also possible to vary them continuously. In some embodiments of the present invention, there is a sensor responsive to ice thickness in a continuous fashion. Yet other embodiments of the present invention permit sensing of a liquid substance (such as rain) by responding to the change in capacitance which results from the placement of the liquid substance proximate to at least one of the electrodes.

One embodiment of the present invention pertains to a fringe-effect capacitor having variable electrode widths, variable electrode gaps, or a combination of variable gaps and variable widths. In one embodiment, the electrode width varies smoothly along the length of the electrode. In another embodiment, the gap between electrodes varies smoothly along the length of the electrodes. In yet another embodiment, both the gap between electrodes and the width of the electrodes varies linearly across the sensor substrate. In a preferred embodiment, the gap between electrodes is smaller where the width of the electrodes is smaller, and the gap between electrodes is larger where the width of the electrodes is larger.

In one embodiment, the sensor includes a plurality of interdigitated fingers of opposing polarities. The width of a finger and the gap between adjacent fingers varies linearly along the surface of the sensor substrate. However, the present invention is not limited to such linear relationships. In another embodiment each electrode includes one or more fingers which are mounted to the surface of the substrate in a spiraling pattern. In yet other embodiments the electrodes are arranged in a circular pattern. Preferably, the width of the electrodes corresponds with the gap between adjacent electrodes, such that wider electrodes are spaced apart by greater gaps and narrower electrodes are spaced apart by narrower gaps. In one embodiment, the width of the electrode and the gap between adjacent electrodes vary smoothly along the length of the electrodes. However, the present invention also contemplates those embodiments in which gap between adjacent electrodes changes discretely (step-wise) along the length of the electrode, and also those embodiments in which the width of the electrode changes discreetly (step-wise) along the length of the electrode. The gap between electrodes is the shortest distance from a point on an edge of one electrode to the closest edge of an adjacent electrode of the other polarity. The width of an electrode is the shortest distance from a point on an edge of one electrode to the opposite edge of the same electrode. The gap between electrodes is the shortest distance from a point on an edge of one electrode to the closest edge of an adjacent electrode of the other polarity. The width of an electrode is the shortest distance from a point on an edge of one electrode to the opposite edge of the same electrode.

FIG. 1 shows an ice sensor 20 according to one embodiment of the present invention. Sensor 20 includes a first electrode 22 and a second electrode 24 placed upon a surface 28 of a substrate 26. First electrode 22 includes a first plurality of fingers 34 which extend on surface 28 from a first side 30 of sensor 20 toward the opposite side 31. Second electrode 24 includes a second plurality 36 of fingers which extend on surface 28 from the second side 31 of sensor 20 toward the opposite side 30. Electrode 22 and fingers 34 are connected into a circuit (shown in FIG. 33) at a first polarity. Second electrode 24 and fingers 36 are interconnected to the sensing circuit at a second polarity. Substrate 26 and fingers 34 and 36 are adapted and configured to operate as a laterally-fringing or fringe-effect capacitor. In some embodiments, an electronically conductive shield (not shown) is placed on the bottom surface of substrate 26 (the surface opposite of surface 28). In those embodiments having the conductive shield, sensor 20 is one-sided with the fringe-effect working only from surface 28. On those embodiments of sensor 20 not having a shield, the fringe-effect operates to both planar sides of the substrate. FIG. 32 gives one example of a circuit 50 as used with some embodiments of the present invention. Circuit 50 includes an oscillator 51 which provides an input to sensor 20 and into a reference capacitor 53. The output of these two capacitors is fed into opposing points of a quad diode ring 52. One intermediate point of ring 52 is provided a reference voltage. The other intermediate point of ring 52 is sent to an analoge buffer, which provides a DC output representative of the ratio of sensor 20 to reference capacitor 53. In one embodiment, sensor 20 provides a capacitance of anywhere from about 0 picofarads to about 200 picofarads. Circuit 50 is similar to an RF phase discriminator, and provides a DC output that is proportional to the phase difference of the signals being fed into quad diode ring 52. Another reference to this general type of circuitry can be found in U.S. Patent No. 3,869,676, incorporated herein by reference. In some embodiments, circuit 50 is preferable because of its use of fewer components, and its direct offering of a DC output as opposed to a DC offset.

Some embodiments of circuit 50 were operated with frequency generator 51 providing inputs of either 10 kHz or 100 kHz, although the basic behavior of circuit 50 in some embodiments of the present invention can be observed from a few hundred hertz into the megahertz region. In some embodiments of the present invention, oscillator 51 operates at a fixed frequency. In yet other embodiments, oscillator 51 is a relaxation oscillator, which changes output frequency as the capacitance of sensor 20 changes. In one embodiment of the present invention, a relaxation oscillator was used operating at about 120 kHz.

Frequencies are selected to be in a range where the conductance and capacitance of the substances (such as ice and liquid water) are frequency independent. This allows the effects of ice and water to be separated and permits the true capacitance to be determined. In some of the embodiments shown herein, the distance between electrodes can be as small as about 0.1 mm, thereby providing sensitivity to droplets of that size. FIG. 17 is a graph of capacitance ratio as a function of ice thickness for the apparatus of FIG. 16. FIG. 17 includes a smooth curve 17-1 drawn over various laboratory measurements.

FIG. 18A and 18B show measurements of capacitance taken during testing. FIG. 18A includes curve 18A-1, which shows capacitance as a function of time, and curve 18A-2, which shows temperature as a function of time. Note that the central portion of curves 18 A-I and 18A-2 show relatively constant characteristics indicative of the latent heat of fusion of the water.

FIG. 1 is prepared from a top, substantially planar photograph of a capacitive sensor according to one embodiment of the present invention. As such, FIG. 1 is approximately shown to scale. The distance between the vertical portions of electrodes 22 and 24 (i.e., the distance between the "side rails" of the capacitive "ladder") is approximately two inches.

Sensor 20 includes a repetitive pattern of four interdigitated fingers which is repeated three and one-half times on substrate 26. Electrode 22 includes adjacent fingers 34.1 and 34.2 that extend across substrate 26. Finger 31 has a width that decreases monotonically from side 30 toward sensor centerline 32, and then increases monotonically thereafter as it approaches electrode 24. Finger 34.2 decreases in width monotonically from side 30 toward centerline 32 and then decreases monotonically as the finger approaches electrode 24. Adjacent fingers 34.1 and 34.2 are preferably separated by a fixed gap 42. Electrode 24 includes fingers 36.1 and 36.2 which extend on top of surface 28 of substrate 26 from side 31 toward side 30. Finger 36.1 lies adjacent finger 34.1, and is separated from the facing edge of finger 34.1 by a variable gap 40.1. In one embodiment, the width of finger 36.1 changes across surface 28 as a mirror image of finger 34.1.

A second finger 36.2 of electrode 24 is located adjacent to finger 34.2 of electrode 22. The facing edges of finger 36.2 and finger 34.2 are preferably separated by a variable gap 40.5 that is greatest toward the centerline 32 of sensor 20, and decreasing as the fingers extend from the centerline toward either side.

FIGS. 2, 3, and 4 depict graphically some of the geometric relationships among the four fingers 34.1, 34.2, 36.1, and 36.2. FIG. 2 shows the relationship 72 between the width of a finger of the electrode and the distance from the centerline (zero distance being the centerline 32). Line A represents the width of electrodes 34.1 and 36.1, which increase as the distance from the centerline increases. Line B shows the width of fingers 34.2 and 36.2 decreasing as the fingers extend away from the centerline.

FIG. 3 shows the relationship 74 between the gap between fingers and the distance from the sensor centerline. Line C shows the gap between fingers 34.1 and 36.1, which increases as the fingers extend away from the centerline. Line D shows the gap between fingers 34.2 and 36.2, which decreases as the fingers extend away from the centerline. FIG. 4 shows the relationship 76 between finger gap and finger width for adjacent fingers of opposite polarity. Preferably, finger pair 34.1 and 36.1 shares a similar relationship to finger pair 34.2 and 36.2. In one embodiment and as line G indicates, in locations where width of the finger is small, the gap between fingers of opposite polarity is preferably small. As the width of the finger increases, likewise the gap between facing edges of the opposite polarity fingers likewise increases.

The interrelationships shown in lines A, B, C, D, and G are for adjacent fingers of opposite polarity. However, in some embodiments, the fingers are adapted and configured to form additional pairs of non-adjacent fingers of opposite polarity. For example, finger 36.1 and finger 34.2 constitute another electrode pair of opposite polarity separated by a variable gap. Line E of FIG. 3 shows this gap 40.3 between the non-adjacent fingers. Line E has the same slope as line C but with an offset representing the parallel gap 42. Likewise, line F shows the variable gap between non-adjacent fingers 36.2 and 34.1 of opposite polarity. This gap 40.4 is represented by line F, which has the same slope as line D, but offset by parallel gap 42.

In the descriptions to follow, the use of an N-series prefix in front of an element number (NXX) refers to an element the same as the non-prefixed element (XX), except for the changes shown or described.

FIGS. 10 and 11 show alternate configurations of variable gap and variable width fringe-effect capacitors. FIG. 10 shows a sensor 320 having a pair of electrodes 322 and 324 mounted to a surface 328 of the substrate 326. Electrode 322 includes a spiral-shaped finger 334 adjacent to a finger 336 of electrode 322, substrate 326 and fingers 334 and 336 being adapted and configured as lateral fringing electrodes. Each finger 334 and 336 is of a width that decreases as the finger spirals toward the center of sensor 320. Further, the gap 340 between facing edges of fingers 334 and 336 decreases as the fingers spirals in toward the center of sensor 320. Sensor 320 includes a larger gap 340.1 between electrodes where electrode 338.1 is of a larger width, and a smaller gap 340.2 between the electrodes where electrode 338.2 is of a smaller width. In this manner, fingers 334 and 336 generally follow the relationship 76 described by line G of FIG. 4. FIG. 11 shows a sensor 420 having a pair of electrodes 422 and 424 of opposite polarity placed on a surface 428 of a substrate 426. Electrodes 422 and 424 each include a finger 434 and 436, respectively, which extend along the length of substrate 426. Fingers 434 and 436 of sensor 420 follow the basic relationship 76 depicted in line G, but do so in a discrete or step-wise fashion as shown by line H of FIG. 4. As line H shows, electrode widths 438.1 of a greater amount are separated by gaps 440.1 of a greater amount. As the electrode width 438.2 decreases, so does gap 440.2. Although what has been shown and described is a sensor 20 having a repetitive pattern of interdigitated electrodes, the invention is not so constrained. Other embodiments of the present invention contemplate a single pair of electrodes having a variable width and a variable gap therebetween. As one example, such a sensor could include half of a finger 34.1 adjacent to half of a finger 36.1. Other embodiments include half of a finger 34.2 adjacent to half of a finger 36.2. Further, the present invention contemplates those embodiments which do not include a parallel gap between adjacent electrodes.

FIG. 19 shows a capacitive sensor 620 according to another embodiment of the present invention. It is appreciated that sensor 620 has only four pairs of electrodes, and this geometry can be considered a subset of the electrode pattern shown in FIG. 1 for sensor 20. It is further appreciated that yet another pattern according to another embodiment of the present invention would include a single pair of opposing polarity electrodes, these electrodes being of non-constant width, being separated by a non-constant gap, such that the width of one of the electrodes increases in the same direction as the gap increases between the electrodes. It can also been seen in FIG. 19 that various embodiments of the present invention do not include symmetry about a centerline 632.

FIGS. 5 and 6 show results from testing of sensor 520. A sensor 520 was placed proximate to a quantity of liquid water. FIG. 5 depicts the overall capacitance 66 of sensor 520 as a function of time during exposure of a quantity of water to below freezing temperature. Line 68 shows the temperature of the water as a function of time. Note that the water linearly decreases from about 20 degrees C to about 0 degrees C, and then maintains 0 degrees C for a period of time 70 corresponding to the latent heat of fusion of the quantity of liquid water. At the end of period 70, all of the water has frozen into a solid, and temperature line 68 decreases quickly to the ambient temperature to which the water has been exposed. FIG. 6 shows a cross plot of the capacitance of sensor 520 as a function of the temperature of the water. Note that the overall capacitance 66 of sensor 520 changes from about 500 picofarads to less than 10 pF for the solid ice. Sensor 520 provides a capacitance that changes uniformly from when the quantity of water first begins freezing (i.e. at the beginning of period 70) to when the last of the water is completely frozen (at the end of period 70).

Sensors 20, 520, and 620 are sensitive to and changes capacitance in response to the formation of thin ice (detectable by smaller width electrodes separated by smaller gaps) and also is responsive to and changes capacitance to thick walls of ice at a larger distance from surface 28 (in response to ice formation proximate to wider width electrodes separated by larger gaps). Since the width and gap of the electrodes of sensors 20 and 620 change smoothly from large to small, these sensors are also sensitive to and changes capacitance in response to the formation of various thicknesses of ice. Since these sensors responds uniformly to the creation of ice, it is possible to infer from the measured capacitance the mixed, physical state of the water (part liquid, part solid) as a function of capacitance.

FIGS. 21 show top, side, and bottom views of a packaged sensor assembly 57 according to one embodiment of the present invention, and in some embodiments appropriate for detection of relatively thin layers of ice. Sensor assembly 57 includes a housing 57.1 having a castellated mechanical connector 57.2 for attachment to a surface such as a surface in a refrigeration unit. An electrical connector 57.3 provides input excitation and output excitation to a circuit 50 located within housing 57.1. In one embodiment, a sensor 620 is attached to a surface of housing 57.1, such that sensor 620 is proximate to a location in the refrigeration unit where water is frozen into ice. The packaged sensor assembly 57 of FIGS. 21 is drawn to scale, and in one embodiment, the length of the package as see in FIGS. 21 A, 21B, and 21C is about 40 mm. In that same embodiment, the width of the package as seen in FIGS. 21A and 21C is about 25 mm.

Although what has been shown and described are sensors that change capacitance in the presence of water changing state from liquid to solid, the invention is not so limited. The present invention contemplates inferring the physical state of any substance whose dielectric constant changes as the substance changes from one state to another. Further, the present invention calculates measurement of other properties and characteristics of a material as the dielectric constant of the material changes at different distances from the sensor.

FIG. 16 is a top plan view of a planar capacitor as known in the prior art. Capacitor 10 includes a first electrode 11 having a relatively large geometry, and a third electrode 13, having a relatively small geometry. An intermediate electrode 12 includes geometries compatible with both first electrode 11 and third electrode 13. FIG. 7 is a schematic representation of an icemaker according to one embodiment of the present invention. Ice making system 80 includes a movable assembly 82 of individual containers 84 located within a sub-freezing environment. Each container 84 is provided with water from a source 86. A motor 89 turns one or more pulleys which cause the assembly 82 5 to be conveyed toward a storage bin 90. An electronic controller 88 sequences the operation of water source 86 and motor 89.

Controller 88 receives signals preferably from one or more sensors 20 or sensors 620 which indicate the physical state of the water within the adjacent container. In one embodiment, a sensor 20.1 changes capacitance as the water within container 84.1 changes its 0 dielectric constant, and thereby influences the fringing electrical fields of sensor 20.1. In some embodiments, there is a second sensor 20.2 located proximate a second container 84.2. Based upon the changes in capacitance of sensor 20.1 and sensor 20.2, controller 88 actuates motor 89 (and in some embodiments container warming circuits or other features, not shown) to cause container 84.1 to drop a partially-frozen ice cube into bin 90. Preferably, bin 90 is 5 also exposed to a sub-freezing environment, and the ejected ice cube continues losing heat within bin 90 and becoming fully frozen. By ejecting partially frozen ice cubes, the freezing cycle is split between assembly 82 of containers 84 and bin 90. The residence time of a cube in containers 84 is shortened since the completion of the freezing cycle is performed within the collection bin 90. Thus, it is possible to create a larger quantity of ice in a given time.

ZO Alternatively, it is possible to create a given amount of ice with fewer containers. Sensor 20 also permits other adaptations which speed up and/or increase the efficiency of an icemaker.

FIGS. 8 and 9 depict other embodiments of the present invention. Icemaker 180 includes one or more ice sensors 120 which are incorporated into a wall of certain containers 184. A first ice sensor 120.1 is located in a wall shared by containers 184.1 and 184.3. A

!5 second sensor 120.2 is located in a wall shared by containers 184.2 and 184.4.

Each sensor 120 is the same as the sensor 20, except that there is no electrically conductive shield on the back surface 129 of substrate 120. Therefore, since substrate 126 has a low dielectric constant, the fringing electric fields of electrode 122 and 124 extend from both the top surface 128 and the opposite back surface 129. Therefore, the capacitance of

0 sensor 120.1 changes in relation to the state of the water in compartment 184.1 and also to the physical state of the water in compartment 184.3. For those icemakers in which the cubes are processed in an array of containers in a tray, with one tray adjacent to another, the present invention contemplates a sensor 120 placed such that it responds to the formation of ice in both containers. In some embodiments, this provides a doubling of the capacitive output of the sensor. Further, such placement of the sensor provides an analog averaging of the physical state of the two quantities of water. In some such applications, the omission of a conductive shield on the substrate permits the sensor to operate in a bi-directional fashion.

In some embodiments of the present invention, there is a shared sensor with parallel, constant width electrodes. The gap and width are adapted and configured to respond to a thickness of ice such that the two adjacent ice cubes have sufficient structural integrity to be ejected into a storage bin. In yet other embodiments, the sequencing of the ejection includes a sensor that responds to the thickness of the ice in conjunction with timed operation of the ejection after a certain thickness has formed. Further, other embodiments of the present invention contemplate very thick electrodes that can be used to fill the gap between the ice cubes. Alternatively, other embodiments of the present invention contemplate electrodes that are bent or formed from thin stock but are in close proximity to each of the containers, while providing a single electrical connection point.

FIG. 9 shows an assembly 282 of containers 284 according to another embodiment of the present invention. Assembly 282 includes a plurality of containers 284 arranged side by side. Sensors 220 are the same as sensors 120, except that each sensor is located in a wall shared with a side container.

Some embodiments of the present invention include a sensor in which the interdigitated fingers are arranged according to a fractal pattern. A fractal pattern provides high capacitance per unit area of the substrate and further provides electrodes of varying widths and gap spacings. Further, the electrodes can be configured with a pseudo-fractal pattern. Further contemplated by other embodiments of the present invention are spacefilling fractals, such as Hilbert Curve.

Although what has bee shown and described are methods for making ice using a capacitive sensor, the present is not so constrained. Other embodiments of the present invention include a sensor of any type which produces a signal corresponding to or permitting inference of the physical state of the ice cube, and/or the thickness of the walls of the ice cube, and/or the ability to eject a partially frozen quantity of ice having sufficient structural integrity to be ejected from a container and have the freezing process continue to completion away from the original container.

Another embodiment of the present invention pertains to a method for making ice. The embodiment comprises providing a source of liquid water, a container, and a sensor. The embodiment also includes putting a quantity of liquid water into the container, and exposing the container to a temperature below the freezing temperature or the water. The sensor detects that a first portion of the quantity is frozen and that a second portion of the quantity is liquid. The quantity of water is ejected after said detecting. As another alternative, the embodiment includes freezing the second portion after said ejecting. Alternatively, the embodiment includes putting a second quantity of liquid water into the container after said ejecting and before said freezing. Alternatively, the embodiment includes exposing the ejected quantity of water to a temperature below the freezing temperature of the water after said ejecting.

Yet another embodiment of the present invention pertains to an apparatus for making ice. The embodiment comprises a source of water. The embodiment also includes a first container and a second container, said first and second containers sharing a wall, said first and second containers being exposed to a temperature less than the freezing temperature of the water. The embodiment also includes an electronic sensor placed proximate the shared wall, said sensor producing a signal corresponding to a first partially frozen quantity of ice in said first container and a second partially frozen quantity of ice in said second container. Alternatively, the embodiment includes that said sensor is placed in the shared wall. As another alternative, the embodiment includes said that the sensor changes capacitance in relation to physical state of the water.

A further embodiment of the present invention pertains to a capacitor. The embodiment comprises a substrate having first and second opposing sides and a surface therebetween. The embodiment also includes a first electrode mounted on the surface proximate the first side, said first electrode having a first finger extending toward the second side, said first finger having a variable width. The embodiment also includes a second electrode mounted on the surface proximate the second side, said second electrode having a second finger extending toward the first side, said second finger having a variable width, said second finger being spaced apart from said first finger by a variable gap. Alternatively, the embodiment includes that the surface is a first surface, said substrate having a second surface opposite of said first surface, and which further comprises an electrical shield on said second surface. As another alternative, the embodiment includes that the surface is a first surface, said substrate having a second surface opposite of said first surface, and that said second surface is not electrically shielded. Another embodiment of the present invention pertains to a method for making ice.

The embodiment comprises providing a source of liquid water, a first container, a second container, and a sensor. The embodiment also includes putting a first quantity of liquid water into the first container putting a second quantity of liquid water into the second container. The first container and the second container are exposed to a temperature below the freezing temperature or the water. The embodiment also includes detecting with the sensor that a first portion of the first quantity is frozen and that a second portion of the first quantity is liquid. The second quantity of water is ejected after said detecting. Alternatively, the embodiment includes wherein said detecting is by sensing the capacitance of the first quantity.

Another embodiment of the present invention pertains to an apparatus for sensing ice. The embodiment comprises a substrate having first and second opposing sides and a surface therebetween. The embodiment also includes a first electrode mounted on the surface and a second electrode mounted on the surface, said first and second electrodes being substantially parallel to each other, said first electrode and said second electrode being configured in a fractal or pseudo-fractal pattern, said pattern being adapted and configured to provide a variable capacitive response when proximate to ice having a thickness from about one tenth of an inch to about three tenths of an inch. Alternatively, the embodiment includes that the pattern is a Hilbert Curve.

FIG. 12 shows an ice sensor 520 according to another embodiment of the present invention. Sensor 520 includes first and second electrodes, 522 and 524, respectively, placed upon a surface 528 of a substrate 526. First electrode 522 is in electrical communication with a first capacitive element 534 and second electrode 524 is in electrical communication with a second capacitive element 536. Each capacitive element 534 and 536 is of a curved shape, with element 536 being separated from element 534 by a substantially uniform gap 540.3. Elements 534 and 436 are adapted and configured to act as electrodes having fringe-effect capacitance.

In the embodiment shown in FIG. 12, capacitive elements 536 and 534 are generally hemispherical in nature. Preferably, each capacitive element 534 and 536 is of a uniform width 538.4 and 538.3, respectively. Further, the two capacitive elements are preferably spaced apart by a gap 540.3 of substantially uniform width. Referring to FIG. 12, which is a photograph and therefore approximately to scale, the outside radius of element 534 is about one inch. The width 540.3 and 538.3 of the electrodes is each approximately one-fourth inch. 5 The gap 540.3 is approximately one-fourth inch.

Although a sensor having uniform width capacitive elements separated by a gap of uniform width has been shown and described, the present invention is not so limited. The present invention also contemplates those embodiments in which the curved capacitive elements are of variable width as previously described, and also in which the gap between 0 electrodes is of a variable width, as previously described.

FIGS. 13A and 13B depict another embodiment of the present invention in which sensor 520 is adapted and configured to fit on a container 584.1 for making ice. Preferably, the capacitive elements 534 and 536 follow the general shape of the ice container 584.1, with the gap 540.3 being located away from the edges of the container 584.1 and placed toward 5 the interior volume of the container. With such placement of the gap, it has been found that the sensor will provide a measurable capacitive change as the water in the interior of the container 584.1 changes phase.

FIGS. 14A and 14B depict an ice container 584.2 incorporating an alternative sensor 520.2. Sensor 520.2 is similar to sensor 520 except that the overall semi-circular shape of the 0 capacitive elements constitutes less than a hemispherical arc. The present invention also contemplates those embodiments in which the shape of the ice container is not hemispherical as shown in FIGS. 13A and 14A. For example, the present invention also contemplates those embodiments in which the ice container is of any shape, with a fringe-effect capacitive element sensor mounted on one of the surfaces of the container. Preferably, in these alternate

15 embodiments, at least a portion of the gap between adjacent capacitive elements is placed on the container in a position corresponding to an interior portion of the container in which the water is slower, or more preferably slowest, to change phase.

Another embodiment of the present invention pertains to an apparatus for making ice. The apparatus includes a plurality of containers; each container includes a plurality of sides

>0 which define an interior volume. Each container includes an opening for introduction of water and removal of ice. One side of the container includes a fringe-effect capacitor. In another embodiment, the capacitor includes at least two capacitive elements and a gap therebetween. The capacitor is adapted and configured so that the gap is located on the one side proximate to the middle of the volume.

FIGS. 15 and 17-21 refer to various aspects of different embodiments of the present invention. As one example, FIG. 19 shows a pattern for electrodes for a fringe-effect frost sensor.

FIGS. 15 show schematically the effect of a layer of a substance interacting with the electrical fields of a fringe effect capacitor. FIGS. 15 A shows a sensor 20 located on a substrate 26. Electrodes 22 and 24 support an electrical flux field 2 IaI. In substrate 26 and a first, relatively small relatively small electrical flux field 21bl outside of substrate 26. FIG. 15B shows the effect of a thin layer of a substance 19 (such as water) which is proximate to electrodes 22 and 24. The external flux field 21b2 is enlarged by the presence of substance 19, thereby causing the capacitance of sensor 20 to increase. FIG. 15 shows sensor 20 having a thicker layer of substance 19 on top of electrodes 22 and 24 and substrate 26. Outside electrical flux field 21b3 is larger yet, indicating a further change in the capacitance of sensor 20. In all three of FIGS. 15 the flux lines 21al, 21a2, and 21a3 are substantially unchanged by substance 19, at least as a first order approximation.

Again referring to FIGS. 15, the flux fields 21bl are supported in air, which has a dielectric constant of about 1. The electrical fields 21b2 and 21b3 are increased as a result of contact with a substance. For those embodiments in which substance 19 is ice, the dielectric constant is about 3, and it can be appreciated that sensor 20 responds to the change in a portion of its dielectric from 1 to 3. In those embodiments where the sensor is placed in contact with liquid water after exposure to air, it can be appreciated that the sensor responds even more robustly to having at least part of its dielectric change from 1 to 80.

Therefore, capacitive sensors according to some embodiments of the present invention can measure the presence and/or thickness of frost on a surface or presence of solid ice for ice cube production. Some embodiments can differentiate between solid ice, ice with air or water entrapped, or slush. Some embodiments can be preset in terms of sensor configuration and circuit characteristics for measuring various thicknesses of frost or ice. Further, the methods and apparatus described herein permit the production of ice cubes based upon the actual state and condition of a specific cube, and not simply a predetermined model of that ice cube. FIG. 20 is schematic representation of adjacent pairs of electrodes on a substrate. The first pair of electrodes includes electrodes 34.01 and 36.01 of opposing polarities. The second adjacent pair of electrodes on the substrate is 34.02 and 36.02, with polarities corresponding to those of the first pair. Likewise, some embodiments of the present invention include third and fourth pairs of adjacent electrodes, also with alternating polarities.

It has been determined analytically that the response of a single electrode (electrode 34.01 in FIG. 20) can be affected by flux fields shared by a plurality of electrodes of the opposite polarity (electrodes 36.01, 36.02, 36.03, and 36.04 in FIG. 20). Curve 20-1 is a graphical representation of a flux line between adjacent conductors. Relatively small amounts of water proximate to electrodes 34.01 and 36.01 result in a "local" effect on system capacitance. The small amount of water (which may be limited by surface tension, small ice or snow particles, etc.) do not affect other electrodes since the extent of water is localized. However, for a larger amount of water which extends from electrode 34.01 to electrode 36.02 of the second pair (such as would be caused by a larger water droplet or larger build-up of frost) will result in a flux line being shared by electrode 34.01 and non-adjacent electrode 36.02. Curves 20-3 and 20-4 illustrate that progressively larger amounts of water or ice on the surface of the electrodes result in the sharing of electrical flux from a first electrode 34.01 of a first polarity, with non-adjacent electrodes 36.01, 36.02, 36.03, and 36.04 of a second, opposite polarity. It is understood that the greater the separation distance to the non-adjacent electrodes, the lower the contribution of that flux will be to the overall signal.

FIGS 22-31 pertain to yet another embodiment of the present invention for making ice. In the descriptions to follow, the use of a 1 Y-series prefix in front of an element number (IYXX) refers to an element that is the same as the one thousand prefixed element (10XX), except for the changes shown or described. Some embodiments of the invention pertain to the use of a capacitive ice sensor for detecting the transition of water from the liquid to the solid states. Note that the invention is not limited to water, and is applicable to any substance which has different capacitive characteristics in the liquid and solid states.

One embodiment of the invention pertains to the use of a portion of the ice making apparatus as an integral part of the capacitive sensor. As will be discussed below, ice makers having evaporator tubes proximate to the ice can use a tube as one electrode of a two- electrode capacitor. However, the present invention is not limited to using a refrigerant evaporator tube as one capacitive electrode. The present invention also contemplates those embodiments in which other portions of the ice making apparatus are used as one electrode in a capacitive sensor. Preferably, the part of the ice maker selected as a capacitive electrode should have good conductivity and be located proximate to at least one location where ice is formed.

In some embodiments of the present invention a second electrode of the capacitive ice sensor is a conductor which is placed in the ice making container in a pattern corresponding to the location and shape of the formed ice. As one example, the second electrode can be a wire, foil, tube, or other cross-sectional shape which is suspended within the ice making container, embedded in the walls or other structure of the container, adhered to the container, coated on a surface of the container, or otherwise placed in locations which correspond to formation of ice. However, other embodiments of the present invention are not constrained to use of a second electrode as described. The present invention also contemplate those embodiments in which the second electrode is a second part of the ice making assembly, such as a container wall or other structure, water inlet, or other component. Preferably, the second electrode is not in electrical communication with the first electrode, except for the capacitive field of the water being frozen.

In some embodiments of the present invention, ice is formed proximate to an evaporator of a refrigeration unit, the evaporator being suspended within a bath of liquid water. The wall thickness of the ice continues to increase as cold refrigerant is pumped through the evaporator. In those embodiments where the evaporator has a plurality of downward-depending fingers, the ice forms around the individual fingers, and the wall thickness of these individual ice shapes continues to increase as more time is spent with a sub-freezing evaporator. By monitoring the wall thickness of the forming ice with a capacitive sensor, the ice making process can be terminated at a time when the measured ice wall thickness (as inferred from the change in capacitance) is within a predetermined range. At that time, the sub- freezing temperature of the evaporator tube is ended as a result of the electronic controller's operation of the refrigerant unit, and the evaporator tube can be warmed to permit the ice shape to be released from the finger.

This inventive method operation is in contrast with a current method of operation, in which the wall thickness of the ice shape is inferred from the amount of time during which the evaporator has been at a sub-freezing temperature. In this timed manner of operation, there is a possibility of the ice from adjacent fingers joining together into one or more ice shapes that are too large. This type of improper operation can result when a timed ice maker is interrupted in a first cycle such that it provides too much time with a sub-freezing finger in a subsequent second cycle.

In yet other embodiments of the present invention, the water is placed in a plurality of individual containers which correspond to the size and shape of the final ice cube. This entire container is immersed within a sub-freezing volume. In such embodiments, capacitive ice sensors can be used to infer the wall thickness, which also corresponds to the volume of unfrozen water contained within the walls of the partially frozen cube.

Although what is being shown and described pertains to capacitive sensors for detecting the formation of ice in an ice maker, the invention is not so limited. Other embodiments of the present invention pertain to apparatus and methods for sensing the formation of ice on vehicular road ways, leading edges of an aircraft wing, inlets of jet engines, and other locations where it is desirable to detect the formation of ice.

One embodiment of the present invention is shown in FIG. 22. Ice making system 1020 uses a finger-type evaporator of the refrigeration system as one of the two electrodes of a capacitive ice sensor. The finger-type evaporator is an integral part of the ice maker 1020 where the ice cubes are formed. One way to make ice cubes involves using a multiple finger (12 fingers are common) evaporator where the closed-end fingers 1032 are suspended in a water bath in a container 1024. Referring to FIGS. 22 through 28, the fingers 1032 extend from a common evaporator tube assembly 1030 arranged in a U-shape. FIG. 32 is drawn from a photograph of portions of an ice maker 120 according to one embodiment of the present invention. Closed-end finger 1032 can be seen depending downwardly from evaporator tube 1030. Container 1024 is shown partly rotated downward away from finger 1032. Cold refrigerant is introduced through the inlet 1030a of the condenser tube. The warmed refrigerant exits through outlet 1030b of tube 1030. As is common in ice making assemblies, the refrigerant is warmed as it removes heat from water surrounding the individual fingers 1032 during the freezing process. Although a U-shaped evaporator tube with fingers has been shown and described, the invention is not so limited, and contemplates the use of evaporator tubes of any shape, including linear, circular, and spiral. As the ice making operation progresses, the refrigerant within the evaporator tube fingers chills the water surrounding each of the fingers, causing it to freeze and form an increasingly thick wall. The overall shape of the resulting ice cube 1026 can be described as having a thimble shape. FIGS. 23 A and 23B are side and top views, respectively, of an ice cube 1026 as formed in ice making system 1020. Cube 1026 includes a pocket 1027 which formed around a corresponding finger 1032. Although what has been shown and described are thimble-shaped ice cubes formed about evaporator-tube fingers, the present invention is not so limited, and contemplates formation of ice in any shape, including for example, cubes and sheet. FIG. 24 is a schematic representation of a top view of a portion of the ice maker of

FIG. 22. A two by two array of fingers 1032 is shown. Ice cubes 1026 corresponding to those fingers are shown formed. In one embodiment, the formed tubes have a wall thickness of about .35 to .4 inches, leaving a gap of .1 to .2 inches between adjacent ice cube walls. The evaporator fingers have a diameter of about .4 to .5 inches. These dimensions are by way of example only, and are not constraints on any embodiment of the present invention.

Referring again to FIG. 22, ice making system 1020 includes a capacitive sensor formed from a first electrode 1034 and a second electrode 1040. First electrode 1034 is in electrical communication with condenser tube assembly 1030, including the plurality of fingers 1032. As discussed previously, this first electrode is not limited to a condenser tube of an ice making system but could also be a different, electrically-conductive portion of the ice making system in proximity to the formed cubes.

The second electrode 1040 is placed within the ice making container 1024 (or could be embedded in container 1024) in regions of the ice making system 1020 where ice forms. The second electrode 1040 of system 1020 includes two strips of electrical conductor 1040al and 1040a2. Evaporator tube 1030 and its plurality of fingers 1032 are U-shaped between this pair of second electrodes of the capacitive sensor. Many different configurations are possible for the second electrode 1040. The second electrode should be physically separated from the first electrode and electrically isolated from the first electrode. One example of a configuration for the second electrode 1140 is a loop as shown in FIG. 25, where the second electrode surrounds all of the fingers of the first electrode in a manner that follows the wall of the water bath. Other examples of locations are the inner wall 1124a of container 1124, the outer wall 1124b of container 1124, or molded within the walls of container 1124. Good sensor performance has been achieved on the inner wall (as shown in FIG. 25), due to absence of the plastic wall of the container or portions of the plastic wall in the other two configurations mentioned.

FIG. 22 depicts an ice making system 1020 according to one embodiment of the present invention. Ice making systems 1020 includes a capacitive ice sensor in which the first electrode is evaporator tube 1030 along with its fingers 1032. A lead wire 1034 is in electrical communication with evaporator tube 1030, and is also in electrical communication with the capacitive measurement circuitry. The second electrode of the capacitive ice sensor comprises the two strips of conductors 1040al and 1040a2. These spatially separated conductors are in electrical communication so as to act as a single electrode of the capacitive ice sensor.

FIG. 25 depicts an ice making system 1120 according to one embodiment of the present invention. Ice making systems 1120 includes a capacitive ice sensor in which the first electrode is evaporator tube 1130 along with its fingers 1132. A lead wire 1134 is in electrical communication with evaporator tube 1130, and is also in electrical communication with the capacitive measurement circuitry. The second electrode of the capacitive ice sensor includes conductive electrode 1140b which loops around the periphery of the evaporator fingers 1132. A lead wire (not shown) places electrode 1140b in electrical communication with the capacitive measurement circuitry. FIG. 26 depicts an ice making system 1220 according to one embodiment of the present invention. Ice making systems 1220 includes a capacitive ice sensor in which the first electrode is evaporator tube 1230 along with its fingers 1232. A lead wire 1234 is in electrical communication with evaporator tube 1230, and is also in electrical communication with the capacitive measurement circuitry. The second electrode of the capacitive ice sensor comprises a conductor 1240c which is configured in a scallop pattern. These scallops correspond generally to the final shape of the harvested ice cube. A lead wire (not shown) places conductor 1240c in electrical communication with the capacitive measurement circuitry. Although a scalloped shape has been shown and described, other embodiments of the present invention include electrode shapes that generally correspond to ice cubes of different shapes, such a as rectangular ice cube.

FIG. 27 depicts an ice making system 1320 according to one embodiment of the present invention. Ice making systems 1320 includes a capacitive ice sensor in which the first electrode is evaporator tube 1330 along with its fingers 1332. A lead wire 1334 is in electrical communication with evaporator tube 1330, and is also in electrical communication with the capacitive measurement circuitry. The second electrode of the capacitive ice sensor comprises a conductor assembly 134OdO placed centrally within the U-shape of evaporator tube 1330 and within container 1324. Conductor assembly 134OdO include seven downwardly depending (into the paper, as viewed from FIG. 27) pins 1340d2 which extend along at least part of the height of the evaporator fingers 1332. Pins 1340d2 are interconnected by a wire 1340dl. Conductor assembly 134OdO is in electrical communication with the capacitive measurement circuitry. In one embodiment, a pin 1340d2 is present along either side of the finger, such that a two by six array of fingers 1332 would have seven pins as shown in FIG. 27. However, the present invention contemplates as few as one pin which is placed proximate a region in which an ice cube is to be formed.

FIG. 28 depicts an ice making system 1420 according to one embodiment of the present invention. Ice making systems 1420 includes a capacitive ice sensor in which the first electrode is evaporator tube 1430 along with its fingers 1432. A lead wire 1434 is in electrical communication with evaporator tube 1430, and is also in electrical communication with the capacitive measurement circuitry. The second electrode of the capacitive ice sensor comprises a conductive assembly 144OeO placed centrally within the center of the U-shape of evaporator tube 1430 and within container 1424. In one embodiment, conductor assembly 144OeO includes a conductive loop which is arranged to form five diamond-shaped structures 1440e2 interconnected by conductors 1440el. In yet another embodiment, each of the diamond-shaped structures 1440e2' is interconnected from one point of diamond to the nearest point of an adjacent diamond by a single conductor 1440el'. Preferably, the diamond shape conductive structure 1440e2 is located centrally between four adjacent fingers 1432 in a two by two portion of the overall evaporator assembly.

What has been shown and described are second electrodes that have shapes which correspond to a U-shaped evaporator tube with a plurality of downwardly depending fingers. As previously discussed, the present invention contemplates the use of any shape of evaporator tube. Preferably, the second electrode is in a shape which generally corresponds to the shape of the evaporator tube, the shape of the ready-to-harvest ice cube, the ice maker container, the container for an individual ice cube, or combinations of these shapes. In some embodiments of the present invention the first electrode is part of an existing structure within the ice maker, which is a cost effective approach. In the embodiments shown in FIGS. 22 through 28, an electrical connection 1034 is established between the evaporator and the measurement circuit. Referring to any of those figures, this connection can be made 5 by directly connecting to the evaporator or by connecting to an equivalent point within the refrigeration system, such as the liquid line that feeds the evaporator.

The dielectric between the two electrodes changes to provide a change in capacitance that can be measured by the measurement circuit. In this case, the liquid water bath provides that starting dielectric material. As heat is withdrawn from the liquid water during the 0 transition to a solid state of ice, the dielectric of that same volume of water changes from the dielectric constant associated with water to the dielectric constant associated with ice. The dielectric constant of water is about 80 and the dielectric constant of water is about 3. The ratio of dielectric change is therefore about 27 to 1. However, the present invention is not limited to substances having a change in dielectric constant of 27 to 1, and also contemplates 5 those embodiments in which the ratio of dielectric change of the substance undergoing a state change is as low as about 5 to 1.

In some embodiments of the present invention the first and second electrodes of the capacitive ice sensor are provided to a controller which is preferably a digital controller. In yet other embodiments the controller receives a signal corresponding to a temperature within O the ice making container. Preferably, the controller measures the capacitance between the first and second electrodes and in some embodiments provides a correction to that measurement based on the temperature signal.

This transition from a homogeneous water bath to a water bath with ice cubes forming within it can be modeled as a piece-wise integration. This situation can be approximately

15 modeled as many capacitors connected in series, and the analysis considers changing each one of these capacitor elements in sequence. The number of capacitors used in the analysis will relate to the smoothness of the resulting function. Twenty elements can be used to provide a reasonable result.

The initial condition for the analysis of one embodiment of the present invention is a i0 homogeneous water bath where all pieces considered are at the higher dielectric constant of 80. This is modeled by a series of capacitors set to an arbitrary initial capacitance value. The total capacitance value of the series capacitor network is calculated and recorded. As ice begins to form on each of the fingers 1031, it is very thin at first and then becomes progressively thicker. The progress can be divided into discrete elements and analyzed. The first step after the initial condition is one where the first integration element changes completely from water to ice, and the corresponding dielectric constant for this element changes from 80 to 3. In the model, the first element is changed to a capacitance value where the initial value is divided by the ratio of the dielectric constants, or approximately 80/3. The total capacitance value of the series capacitor network is calculated and recorded. The next capacitor is reduced by the same factor to model the next segment of water bath changing completely from water to ice. The total capacitance value of the series capacitor network is calculated and recorded. This continues until the entire water bath has made the transition from water to ice. Note that this model extends further than the actual case of making ice cubes using a finger-type evaporator, according to some embodiments of the present invention, since in some embodiments the ice cubes are harvested before the entire water bath is solid ice. This early harvesting permits higher total throughput of the ice maker, since the ice maker can be used to begin freezing the next generation of ice cubes while the harvested and partially-frozen ice cubes continue to transition to the fully frozen state in a different container in the refrigerated area.

FIG. 29 is a graphical representation of the normalized capacitance of a capacitive ice sensor according to one embodiment of the present invention as a function of the state of the water proximate the sensor as the water changes from the liquid state to the solid state. This relationship 1099 between normalized capacitance and the percent frozen state of the ice can be used for initiating the harvest of one generation of ice cubes when the inferred wall thickness is at a predetermined value, which in some cases is prior to their complete transition to solid state. For example, an electronic controller receives a signal from the capacitive ice sensor. A first measurement of capacitance is made at the time that liquid water is introduced into container 1024. As the freezing cycle begins, the controller makes periodic measurements of the capacitance of the ice sensor. This periodic, or instantaneous, capacitance can be normalized by the initial capacitance to determine how much the capacitance has changed during the freezing cycle. For example, a ninety percent reduction in capacitance is indicative of ice cubes that are about thirty-five percent frozen. A ninety- five percent reduction in capacitance indicates that the ice is about seventy percent to eighty percent frozen. FIG. 30 shows three clusters of measured data that relate the radial wall thickness of an ice cube 1026 (as shown in FIGS. 23A and 23B) as a function of the weight of the cube. For example, if it is desirable to have a radial wall thickness of about .35 to .38 inches, the corresponding cube weight is in a range of about 10.5 to 11.5 grams. FIG. 31 relates the capacitance of the ice sensor verses time for different configurations of the second electrode. Curve 1196 relates capacitance verses time for the loop electrode 1140b as shown in FIG.25. Curve 1296 depicts capacitance verses time for a scalloped second electrode 1240c as shown in FIG. 26. There are three curves 1396 which relate capacitance as a function of time for a five pin array of electrodes, similar to those depicted in FIG.27. FIG. 27 depicts a second electrode 1340 that comprises seven pins 1340d2 extending roughly parallel to fingers 1332, and interconnected by a conductor 1340dl.

FIG. 34 shows an evaporator assembly 1050 according to another embodiment of the present invention. Evaporator assembly 1050 includes one or more tubes 1052 arranged as a heat exchanger, and having a plurality of U-shaped bends 1053. A plurality of fins 1051 are in thermal contact with one or more tubes 1052. Refrigerant or coolant is pumped through tubes 1052. This coolant removes heat from the tubes, and because of the thermal contact with the fins also cools the fins. Air is passed over evaporator 1050 and thereby becomes cooled for subsequent use in a refrigeration or chilling process. In some applications, the fins are spaced apart by about 10 mm or 5 mm. A typical fin thickness is about 0.3 mm. Often, the air being cooled by evaporator 1050 contains humidity, which can precipitate out as frost on fins 1051 and tubes 1052. Sensors of the type described herein can be added to evaporator 1050 to provide a signal indicative of frost formation. In some embodiments of the present invention a frost sensor 20' is placed within a bend 1053 of the tube. In other embodiments, a sensor such as 57' is placed between adjacent fins 1051 and proximate to a portion of tube 1052. The use of a prime designation (') for 57' and 20' indicates a sensor 57 or 20, respectively, as previously described, except adapted and configured for mounting to an evaporator assembly.

In yet another embodiment of the present invention, a sensor 20, 520, 620, or other inventive sensors described herein is utilized for the thawing of frost that has collected on an evaporator. As has been previously discussed, blowing ambient air over an evaporator can result in the formation of frost on the evaporator, and for those embodiments in which a sensor 20 is proximate to the evaporator, formed on the capacitor as well. This accumulation of frost proximate to the electrodes of the capacitor will result in alteration of the flux lines since frost has a different dielectric than air and a subsequent change in the capacitive response of the sensor. This measured change in capacitance can be utilized by an operator (for those embodiments where the change in capacitance results in turning on of a "frost light") or used by an electronic controller to operate a deep defrosting cycle for the evaporator. As is commonly done during a defrost operation, a heated fluid is made to flow within the evaporator, and thereby heat it and the capacitive sensor. As the frost first changes to liquid water, the capacitance of the sensor may increase, because of the higher dielectric constant for liquid water vs. frozen water. Subsequently, the continued application of heat will cause the liquid water to evaporate, with a resultant decrease of the capacitance of the sensor. These changes in capacitance (an increase in going to the liquid phase, and a decrease after evaporation) can be used to signal to the operator that the defrost cycle is complete. Likewise, an electronic controller, sensing the increase and decrease in capacitance, could turn off the source of heat to the evaporator.

In general terms, the measurement circuit according to one embodiment of the present invention provides a capacitive input and an output that can be easily integrated into an ice maker control system, rain sensing system, or into a frost control system. Common outputs would be an analog voltage that varies in response to ice forming on the evaporator fingers, pulse width modulation output, or digital output format.

One embodiment of the present invention pertains to an apparatus for making ice, comprising a container for holding liquid water; a refrigeration unit for removing heat from water in the container; means for sensing the capacitance of water in the container and providing a signal corresponding to the capacitance of the water; and a controller operably connected to said refrigeration unit, said controller operating said refrigeration unit in response to said signal.

In some embodiments said sensing means is a fringe effect capacitor. In other embodiments said fringe effect capacitor has at least two electrodes and water in the container is a dielectric for the two electrodes. In yet other embodiments said sensing means is a capacitor having at least two electrodes and water in the container is a dielectric between the two electrodes. In still other embodiments, one of the electrodes of said capacitor is part of said refrigeration unit. In yet other embodiments said controller is a digital controller having memory, the memory including data which relates the capacitance of the water to a predetermined thickness of ice in said container.

One embodiment of the present invention pertains to an apparatus for sensing the capacitance of water, comprising a refrigeration unit for removing heat from water, said refrigeration unit including a first electrically conductive member located proximate to a location where liquid water transitions to ice; a second electrically conductive member located proximate to the location where liquid water transitions to ice, said first member being electrically insulated from said second member and spaced apart from said second member; and a circuit in electrical communication with said first member and said second member, said circuit producing a signal corresponding to the capacitance of the water between said first member and said second member.

In some embodiments, said first member is an evaporator tube. In other embodiments, said first member has a first shape immersed in water, said second member having a second shape corresponding to said first shape. Other embodiments include a container for holding water, said refrigeration unit capable of removing heat from said container, said container having a shape, said second member having a shape corresponding to the shape of said container.

Another embodiment of the present invention pertains to a method for making ice, comprising providing a container holding liquid water; making a first measurement of the capacitance of the water; removing heat from the water and transitioning some of the liquid water into ice; making a second measurement of the capacitance of the water after said removing; and comparing the first measurement to the second measurement.

In one embodiment of the present invention, said comparing is dividing the second measurement by the first measurement. In other embodiments, said comparing is subtracting one of the second measurement or the first measurement from the other of the second measurement or the first measurement. Other embodiments include determining by said comparing if a predetermined amount of ice has been made. Still other embodiments include stopping said removing heat after said determining. In another embodiment, said providing includes a capacitor for said making s first measurement and said making a second measurement, and at least some of the transitioning water is the dielectric of the capacitor. In other embodiments, said first member has a first shape immersed in water, said second member having a second shape corresponding to said first shape. Still other embodiments include a container for holding water, said refrigeration unit capable of removing heat from said container, said container having a shape, said second member having a shape corresponding to the shape of said container.

FIGS. 35-38 pertain to other embodiments of the present invention. FIG. 35 shows a top planar view of a fringe effect capacitor according to another embodiment of the present embodiment. FIG. 35 shows a capacitive sensor 720 having a plurality of interdigitated electrodes arranged in a fan-shaped pattern. Electrodes 722 and 724 are placed near the center of the fan shape, although these electrodes could be placed at other locations as well. A plurality of first fingers 734 are shown increasing in width 738.1 monotonically from the center in an outwardly radial direction. A second plurality of electrodes 736 preferably increase in width monotonically in the same radially outward direction. Fingers 734 and 738 are spaced apart by a gap 740.1 that increases as the nearby width of an electrode increases. Electrode 722 with finger 734 and electrode 724 with finger 736 are mounted on a surface 728 of a substrate 726. In one embodiment, the diameter of the fan shape is about two inches.

FIG. 36 is a top plan view of a capacitive sensor according to another embodiment of the present invention. FIG. 36 shows a capacitive sensor 820 having two electrodes. Electrodes 822 and 824 extend into adjacent planar fingers or electrodes 834 and 836, respectively. Fingers 836 and 834 are symmetrical about a centerline, and have a greatest width (such as 838.1) at the centerline, where there is correspondingly a widest gap 840.1.

Going away from the centerline, the width of each electrode decreases monotonically, as does the gap between electrodes. However, the present invention is not so constrained, and other embodiments include a single electrode of variable width placed on a substrate alongside a second electrode of constant width, the two electrodes being separated by a variable gap. Further, it is understood for all embodiments of the inventive sensors shown herein that the specific patterns of electrodes shown are but one embodiment. For example, the fan- shape of FIG. 35 could also be one-fourth of a circle, an entire circle, or either two adjacent "pie" or triangular-shaped electrodes. Further, the electrode pattern shown in FIG. 36 could be repeated lengthwise (i.e., extending from the right side of FIG. 36) or, could be interdigitated with other similarly shaped fingers, for example, as would be if emanating from the common rails as shown for FIG. 20. These fingers could also be replicated in an alternating pattern vertically (again referring to the orientation of FIG. 36). Further, for any of the inventive sensors shown herein the patterns can include as few as two electrodes of opposite polarity, or as many electrodes as desired for a particular application.

Figure 37 is a perspective view of a vehicle 900 incorporating a sensor according to one embodiment of the present invention. Sensor 720 is shown installed on a windshield 902

5 of a vehicle 904. In some embodiments, sensor 720 is placed centrally and towards the top of the windshield. Sensor 720 and windshield 902 are adapted and configured to facilitate detection of liquid water such as rain falling on sensor 720. Electrodes 722 and 724 are operably connected to circuitry which measures changes in the capacitance of sensor 720 due to the proximity of rain water, and uses that information to operate systems of the car, such as

LO the windshield wipers.

The sensor 720 responds to a wide range of droplet sizes. Previous attempts to use capacitive sensing have used electrodes based on homogeneous geometry, which is to say that they used electrodes of consistent width throughout the entire pattern. Also there were gaps between the electrodes which were consistent throughout the entire pattern. These

L 5 previously used capacitive sensors were limited by their geometry to detection of rain under limited conditions. In contrast, the inventive sensors shown herein, such as sensors 20, 520, 620, 720, and 820 all incorporate variable electrode geometry and/or variable electrode spacing which provides detectable changes in capacitance for a much wider range of operation.

10 FIG. 38 is an expanded and exploded view of the sensor as shown in FIG. 37. In one embodiment, windshield 902 is automotive safety glass. Automotive safety glass is constructed using two curved "sheets" of glass 902.2 and 902.4 that are bonded together with a butyl layer 926. There are therefore four surfaces: the outer-most (exterior) surface, one where the outer layer 902.2 of glass contacts the inner butyl layer 926, one where the inner i5 butyl layer 926 contacts the other sheet of glass 902.4, and finally one which is the glass surface on the vehicle's interior cabin space. The electrodes 722 and 724 are located on the outer-most surface 928 of the butyl layer 926. The shield layer is on the inner-most surface of the butyl layer, such that the separation distance between the electrodes and the shield corresponds to the thickness of the butyl layer. Preferably, the shield is larger than the

>0 sensing patter. This shield preferably extends beyond the sensor pattern in all directions by a distance of about five times the separation between the pattern and the shield. In another embodiment of the present invention, the substrate material is of the type commonly used in making clear flexible circuits. Further, the electrodes and fingers of sensor 720 can be made from commonly used transparent conductors. In yet other embodiments, these electrodes and fingers are fabricated from copper cladding. While what has been shown and described is the usage of an inventive capacitive sensor with multiple layer safety glass, the present invention is not so constrained, and can also be used with other constructions of glass, and on any non-conductive surface. As shown in FIG. 38, placement of the sensor high on the windshield minimizes any distraction to the driver. However, it is advantageous to place the sensor on a portion of the windshield that is swept by the wipers. In yet other embodiments, the inventive sensors patterns shown herein can be coated with an adhesive and applied to the interior-most surface of the windshield.

While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.

Claims

What is claimed is:

1. A capacitor for sensing capacitance near a surface, comprising: a first electrode mounted on the surface, said first electrode having a first plurality of substantially planar fingers extending on the surface in a first direction, at least a portion of each of said first fingers having a varying width which increases along the first direction; and a second electrode mounted on the surface, said second electrode having a second plurality of substantially planar second finger extending on the surface in a second direction generally opposite to the first direction, at least a portion of each of said second fingers having a varying width which increases in the first direction, each of said second fingers being interdigitated with different ones of said first fingers and spaced apart therefrom by a gap-

2. The capacitor of claim 1 wherein said first fingers are generally triangular in shape.

3. The capacitor of claim 2 wherein said second fingers are generally triangular in shape.

4. The capacitor of claim 1 wherein the gap between at least one pair of adjacent first and second fingers increases along the first direction.

5. The capacitor of claim 1 wherein adjacent pairs of said first fingers and said second fingers coact with fringe-effect capacitance.

6. The capacitor of claim 5 wherein each of said first fingers and said second fingers are adapted and configured such that the fringe-effect capacitance is altered in the presence water.

7. The capacitor of claim 1 wherein the gap between adjacent pairs of interdigitated said first fingers and said second fingers is nonconstant.

8. The capacitor of claim 1 wherein the gap between adjacent pairs of interdigitated said first fingers and said second fingers is constant.

9. A capacitor responsive to a change in dielectric proximate to a surface, comprising: a first electrode mounted on the surface and extending on the surface in a first direction, said first electrode having a first varying width which monotonically increases along the first direction; and a second electrode mounted on the surface adjacent to said first electrode, said second electrode having a second varying width which monotonically increases in the first direction, said second electrode being spaced apart from said first electrode by a gap which increases along the first direction.

10. A fringe-effect capacitor, comprising: an insulating substrate having first and second opposing sides and first and second opposing surfaces; a first electrode mounted on the first surface proximate the first side, said first electrode having a first finger with a first length and extending toward the second side, said first finger having a first variable width; and a second electrode mounted on the first surface proximate the second side, said second electrode having a second finger with a second length extending toward the first side, said second finger having a second width, said second finger being spaced apart from said first finger by a variable gap. wherein the relationship between the first variable width and the variable gap is such that portions of said first finger widen along a direction along the first length, and the gap from the portion of said first finger to said second finger widens along the same direction.

11. The capacitor of claim 10 wherein the second width is a second variable width.

12. The capacitor of claim 10 which further comprises an electrical shield on said second surface.

13. A sensor for measuring the presence of a liquid, comprising: a fringe-effect capacitor having a first electrode and a second electrode separated by a variable gap, one of said first electrode or said second electrode having a variable width, the variable gap between said first and second electrodes increasing as the variable width increases; and an electrical circuit which includes a reference capacitor having an input electrode and an output electrode, a source of oscillating voltage, and at least 4 diodes arranged in a four arm bridge, one of said first electrode or said second electrode and the input of said reference capacitor receiving an input from said source, and the other of said first electrode or said second electrode and the output of said reference capacitor being provided to opposing arms of said bridge.