Contamination-resistant level sensors

Abstract

A liquid level sensor utilizes a high clearance downwardly extending finger and spring to provide a downwardly hanging float supported above the reservoir fill level, preventing encrustation of the float support mechanism. The spring may be a flattened spiral to reduce the height of the sensing mechanism when so arranged. The sensor is sealed within the sensor head and electrically senses the height of the float through the sealed compartment, thereby being resistant to contamination.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application No. 62 / 650,103, filed on March 29, 2018, and U.S. Non-Provisional Application No. 16 / 368,224, filed on March 28, 2019, which are incorporated herein by reference. Technical Field

[0003] The present invention relates to liquid level sensors and the like, and in particular to liquid level sensors suitable for use with liquids (eg, liquid detergents) that can encrust moving parts and interfere with electronic circuits. Background Art

[0004] Modern appliances may include multiple automatic dispensers or reservoirs, for example, for dispensing detergents and detergent aids or for containing clean or contaminated water, and it may be desirable to sense the liquid level to notify the appliance user when these cleaning materials are nearly depleted or when a reservoir needs to be emptied or checked to ensure proper operation of the appliance. In many cases, it may be desirable to be able to distinguish between multiple liquid level heights to provide a more complete picture of the amount of material stored in the dispenser or reservoir.

[0005] It is generally known to sense liquid height by using a float that moves, for example, on an arm or guide as the height of the liquid changes. The position of the float can be monitored electronically, for example, by means of a limit switch. Liquid level sensors that employ an antenna that is partially submerged in the liquid are also known.

[0006] In many cases, the liquid being sensed has significant amounts of dissolved solids that can settle on the moving surface of the sensor (e.g., a float moving along a guide) or can coat the antenna or other electronic sensors in a manner that interferes with their operation. Summary of the invention

[0007] The present invention provides a float supported at its upper edge, which is above the highest expected level of liquid, thereby protecting the float support structure from contamination. A spring biases the float downward to provide a flow movement proportional to the change in liquid height, thereby minimizing the movement of the float to provide an extremely compact support structure and allowing the structure to be better separated from the liquid. The movement of the float is sensed by an inductive sensor that is completely contained in the sensor housing and completely separated from the float and the sensed liquid. Inductive sensing allows for a large gap between the float structure and the sensing head, and also allows for better resistance to interference caused by contamination. Printed circuit coils can be used for this inductive measurement, also providing an extremely low profile sensor head.

[0008] Specifically, in one embodiment, the present invention provides a liquid level sensor having an elongated float and a sensor head provided with a sealed compartment. The sensor head is adapted to be received at an opening in an upper wall of a reservoir and is provided with a downwardly extending guide for supporting the elongated float moving below the sensor head along a vertical axis. A sensor mounted in the sealed compartment senses the height of the elongated float relative to the sensor head, and a spring extending between the sensor head and the elongated float biases the elongated float downward against the buoyancy applied to the elongated float.

[0009] It is therefore a feature of at least one embodiment of the invention to provide a compact float-type liquid level sensor. The vertical movement of the float avoids the horizontal space required for a swing-arm float mount. The spring reduces the vertical movement of the float, thereby reducing the vertical height of the liquid level sensor.

[0010] The downwardly extending guide may be a finger having inwardly extending teeth for engaging an outwardly extending rim on the elongated bottle.

[0011] It is thus a feature of at least one embodiment of the invention to provide an open frame structure that is less susceptible to retaining liquids that may dry and create stickiness between components.

[0012] The outwardly extending rim and inwardly extending teeth have opposing inclined surfaces that provide an upward snap-fit ​​engagement as the bottle moves upward relative to the finger.

[0013] It is thus a feature of at least one embodiment of the invention to provide a simple assembly technique that requires only pressing the float up into the sensor head.

[0014] When the elongated float is in the lowest engaged position, the inwardly extending teeth may be in contact with the outwardly extending rim over less than 25% of the circumferential length of the rim.

[0015] It is thus a feature of at least one embodiment of the invention to minimize contact between the elongated float and the support member that might, for example, contribute to sticking of the material of the sensed liquid.

[0016] The elongated float may extend a first distance below a lowest extension of the downwardly extending guide, the first distance being greater than a second distance above a lowest extension of the downwardly extending guide.

[0017] It is therefore a feature of at least one embodiment of the invention to displace the float and its contact with the liquid below the sensor head and its guide to reduce the risk of accumulation interfering with the movement of the float.

[0018] The level sensor spring may be constructed from a polymer material.

[0019] It is thus a feature of at least one embodiment of the invention to allow exposure of the spring to facilitate drainage and assembly while resisting corrosion.

[0020] The spring may be mounted above a lowermost extension of the downwardly extending guide.

[0021] It is therefore a feature of at least one embodiment of the invention to provide adequate guidance for the float to facilitate linear motion by separate float guidance points at the spring and at the lower extension of a downwardly extending guide below the spring.

[0022] The spring may be a sheet of planar material having a spiral groove and a central opening, attached to the elongated float to extend perpendicular to the vertical axis, and having an outer periphery attached to a surrounding wall of the sensor head.

[0023] It is thus a feature of at least one embodiment of the invention to provide a low profile spring that is highly resistant to contamination.

[0024] The outer periphery of the spring may be provided with radially extending tabs which flex downwardly to pass upwardly through the lower edge of the surrounding wall and then flex outwardly to engage corresponding holes in the surrounding wall when aligned therewith.

[0025] It is thus a feature of at least one embodiment of the invention to allow simple assembly of a level sensor by pressing a spring-retained float upward into a sensor head.

[0026] The tabs may engage with the corresponding apertures at relative locations between the elongated float and the sensor head prior to engagement between the downwardly extending guide and the elongated float.

[0027] It is therefore a feature of at least one embodiment of the invention to provide a slight preload to the spring to minimize bounce such as could produce sensor errors.

[0028] The sensor may be an inductive sensor, and the upper portion of the elongated float is provided with an upwardly extending inductive element at the top of the elongated float.

[0029] It is thus a feature of at least one embodiment of the invention to provide a sensor system that does not require close contact between the float and the sensor head that could result in sticking.

[0030] The sealed compartment may include an inwardly extending pocket for accommodating the upwardly extending inductive element.

[0031] It is thus a feature of at least one embodiment of the invention to allow the sensing electronics to be completely sealed from the liquid being sensed.

[0032] The inductive sensor may be provided with an antenna formed as a spiral on a cladding of a printed circuit board having a hole that fits around the inwardly extending pocket.The cladding and spiral may be at the bottom of the printed circuit board, towards the elongated float.

[0033] It is thus a feature of at least one embodiment of the invention to provide close proximity between a sensor antenna and a sealed sensor system.

[0034] The inductor element may be a ferrite element.

[0035] It is therefore a feature of at least one embodiment of the invention to provide an inductive element that is easy to sense and also resistant to corrosion.

[0036] The elongated float may be a polymeric container having an enclosed air pocket sealed within the bottle and wherein the container has a substantially constant cross-sectional area in a portion of the container extending below the downwardly extending guide.

[0037] It is therefore a feature of at least one embodiment of the invention to provide a robust, corrosion-resistant float that provides an upward buoyancy force proportional to liquid height to improve sensing linearity.

[0038] The sensor may further include a reservoir, wherein the reservoir may have fill level markings indicating a maximum fill level of the reservoir, and the downwardly extending guide may be above the fill line markings when the sensor head is mounted on the reservoir.

[0039] It is thus a feature of at least one embodiment of the invention to provide a sensor system that resists contamination that prevents free movement of the float relative to the sensor head by moving contact between the sensor head and the float above a maximum height.

[0040] Other features and advantages of the present invention will become apparent to those skilled in the art from a review of the following detailed description, claims and accompanying drawings, in which like reference numerals are used to represent like features. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1is a perspective view of one embodiment of a liquid level sensor of the present invention positioned above a reservoir shown in partial cross-section, the liquid level sensor for measuring liquid within the reservoir, the liquid level sensor including a sensor head supporting a pendant float;

[0042] Figure 2 is a perspective fragmentary view of the upper portion of the float attached to a helical cut spring plate for biasing the float downwardly and showing a sensor plug holding a ferrite cylinder attached to the upper end of the float for passing through an aperture in a printed circuit board holding a disc coil and inductance measurement circuitry for measuring the height of the float;

[0043] Figure 3 It is due to Figure 2 Schematic side elevation view of a float in two positions biased by a spring, showing the operation of the spring to reduce float movement to a small fraction of the change in liquid height;

[0044] Figure 4 It is along Figure 1 The elevation section along line 4-4 shows Figure 1 The internal arrangement of the sensor head and the float components;

[0045] Figure 5 is a partial view of a finger extending downwardly from the sensor head showing the teeth which may be flexed to engage a rim on the float.

[0046] Before describing the embodiments of the present invention in detail, it should be understood that the present invention is not limited to the construction details and component arrangements set forth in the following description or illustrated in the accompanying drawings. The present invention can have other embodiments and can be practiced or implemented in a variety of different ways. Moreover, it should be understood that the wording and terminology used in this article are for descriptive purposes and should not be considered as restrictive. The use of "including" and "comprising" and their variations is intended to cover the items listed thereafter and their equivalents and to cover additional items and their equivalents. DETAILED DESCRIPTION

[0047] Now refer to Figure 1The liquid level sensor 10 of the present invention may include a sensor head 12 located above and supporting a pendant float 14. The float 14 may be, for example, a closed, elongated, hollow polymer cylinder having a cylinder axis aligned with a vertical sensor axis 15. The upper end of the float 14 may be held by a set of fingers 16 extending downwardly from the sensor head 12 to support a rim 18 surrounding the upper end of the float 14, thereby allowing the float 14 to move upward relative to the sensor head 12 along the axis 15.

[0048] The body of the float 14 can pass through a circular opening 20 in an upper wall 22 of a fluid container that contains a fluid 26 (e.g., detergent, detergent aid, water, or contaminated water) whose level 28 must be sensed. The circular opening 20 can be positioned within a threaded neck ring 30 that engages a corresponding neck ring 31 on the sensing head 12 so that the two neck rings can be securely attached together during use, such as by slight relative rotation. The maximum fill height 27 that the fluid container 24 has can be indicated by a molded mark or other reference indication indicating the maximum liquid height. The fingers 16 terminate above this level so that the fingers are generally clear of contamination.

[0049] The sensing head 12 provides sensor electronics for sensing the position of the float 14 relative to the sensing head 12 as described below, with the sensor electronics providing signals via a connecting harness 33 which in turn may also provide power to the housed electronics.

[0050] Now refer to Figure 2 and Figure 4 , the float 14 can be a generally cylindrical bottle having a constant cross-section over those portions below the rim 18 to provide a predictable restoring force as the liquid level rises. The float 14 can be constructed of a corrosion-resistant polymer material and can have an internal sealed air pocket. The upper end of the float 14 can support an upwardly extending, generally cylindrical sensor plug 32 that is coaxially disposed along the axis 15 and has a reduced diameter relative to the diameter of the float 14. The sensor plug 32 can support a cylindrical ferrite 34 on its outer surface that can extend upward into the sensor head 12 as the float 14 moves along the axis 15. In this regard, the sensor head 12 provides an enclosed, sealed volume 36 that is protected from environmental contaminants and includes an upwardly extending pocket 38 at its lower surface that extends into the enclosed volume 36 so that the sensor plug 32 and the ferrite cylinder 34 can move into the pocket 38 as the float 14 rises (corresponding to a rise in the liquid level 28).

[0051] The coil spring 40 is generally a thin disk of metal or polymer material that provides a set of concentric spiral grooves that provide a restoring force that presses downward on the float 14 to resist the float 14 from moving upward into the pocket 38 as the coil spring 40 moves out of its planar configuration. The outer periphery of the coil spring 40 may be attached to the structure of the sensor head 12 above the finger 16, and the inner periphery of the coil spring 40 may be attached to the plug 32 just below the ferrite cylinder 34 and spaced from the pocket 38. In addition to providing a bias along the axis 15, the coil spring 40 may also provide a restoring force that maintains the float 14 in axial alignment along the axis 15. Generally, when the coil spring 40 is in the relaxed planar configuration, the extension of the coil spring will extend perpendicular to the axis 14. To facilitate installation, the outer periphery of the coil spring 40 may have tabs 41 which fit into corresponding holes or recesses in the wall of the sensor head 12 surrounding the coil spring 40, and may be installed by pressing upwards on the float 14 with the coil spring 40 engaged until the tabs slide over the ramp surface 17 and snap into place in the wall of the sensor head 12. At this point, the rim 18 will be over the teeth 62 so those teeth will also be engaged.

[0052] The enclosed volume 36 of the sensor head 12 holds a circuit board 42 having a central aperture 44 coaxially about the axis 15 and fitting about the upwardly extending pocket 38, thereby allowing the sensor plug 32 and the ferrite cylinder 34 to move into and through the plane defined by the lower surface of the circuit board 42. However, the circuit board 42 is completely isolated within the volume 36 from the environment to which the sensor plug 32 is exposed.

[0053] The lower surface of the printed circuit board 42 supports a spiral conductor 46, which may be a loop antenna etched into the copper cladding of the circuit board 42 and providing an inductor representative of the inductance. In an alternative embodiment, a standard bobbin wound coil (copper wire wound around a bobbin) may be used to provide a denser flux pattern that is more resistant to external metallic elements. Movement of the ferrite cylinder 34 toward and away from the spiral conductor 46 changes the inductance of the spiral conductor 46, which may be measured by a measurement circuit 48 supported on the other side of the printed circuit board 42. Such a measurement circuit 48 may, for example, provide a resonant circuit that generates an oscillation using the inductance of the spiral conductor 46, the frequency of which is monitored, for example, by counting or other means, to provide an electrical value that may be associated with the vertical position of the float 14 relative to the sensor head 12. The circuit 48 includes a threshold sensor to compare the electrical value to a threshold value so that the circuit 48 can output (via connector 52 to the wiring harness 33) an electrical signal that provides a single binary value to indicate that the float 14 is above or below the threshold value, or provides an analog value (analog voltage, analog frequency, or binary number) to indicate a range of positions of the float 14 relative to the sensor head 12. Generally, it should be understood that the circuit board 42 is a thermoplastic material, such as fiberglass, and is therefore electrically non-active in terms of affecting the inductance of the spiral conductor 46.

[0054] Now refer to Figure 2 and Figure 3 , the coil spring 40 controls the ratio between the change in height of the liquid level 28 (e.g., from 28a to 28b) and the change in height 54 of the float 14, thereby allowing a relatively small movement of the float 14 to be associated with a relatively large change in the liquid level 28, thereby accommodating the sensitivity of the inductive sensing system and allowing a more compact sensing head 12. This compactness in height of the sensing head 12 further benefits from the flat form factor of the coil conductor 46.

[0055] The neck ring 31 of the sensor head 12 may be provided with an O-ring 64 to seal the sensor head 12 relative to the container 24 when mounted to be retained by a twist lock or threads (not shown).

[0056] Refer again Figure 4 And also refer to Figure 5To facilitate assembly, the upper edge of the rim 18 of the float 14 may have an outwardly and downwardly inclined surface 61 to allow the float 14 to snap into place within the fingers 16 by causing the inclined surface 61 to press outwardly against the correspondingly inclined lower surface 60 of the inwardly extending teeth 62 on the lower end of the fingers 16 when the float 14 is pressed upward. This upward movement of the float 14 seats the periphery of the coil spring 40 against the downwardly facing retaining flange of the sensor head 12. In this regard, the inwardly extending teeth 62 may be arranged to be circumferentially displaced from the downwardly extending portion of the fingers 16 to allow engagement and disengagement by a slight twist 63 of the fingers 16, thereby allowing the other portions of these fingers to remain well aligned with the axis 15. Generally, the circumferential extension of the teeth 62 will be much less than 25% of the circumferential length of the rim 18 to reduce the possibility of sticking between the two being greater than the force applied to the float 14.

[0057] The distance that float 14 extends below rim 18 should be greater than the distance that it extends above rim 18, and generally the same relationship is true relative to the lowest downward extension of finger 16, so that the engagement between rim 18 and teeth 62 can be located away from the surface of the liquid being measured.

[0058] Certain terms are used herein for reference purposes only and, therefore, are not intended to be limiting. For example, terms such as "upper," "lower," "above," and "below" refer to directions in the referenced drawings. Terms such as "front," "rear," "back," "bottom," and "side" describe partial orientations of components within a consistent but arbitrary frame of reference, which is clear by reference to the context and related drawings describing the components in question. Such terms may include the words specifically mentioned above, their derivatives, and words of similar meaning. Similarly, unless the context clearly indicates otherwise, the terms "first," "second," and other numerical terms referring to structures do not imply a sequence or order.

[0059] When introducing elements or features of the present disclosure and exemplary embodiments, the articles "a, an," "the, said," are intended to indicate the presence of one or more elements or features. The terms "comprising, including," and "having" are intended to be open ended and indicate that other elements or features may be present in addition to the elements or features specifically noted. It should be further understood that the method steps, processes, and operations described herein should not be interpreted as necessarily requiring them to be performed in the particular order discussed or shown, unless the order of execution is specifically noted. It should also be understood that additional or alternative steps may be employed.

[0060] It is specifically intended that the present invention is not limited to the embodiments and illustrations contained herein, and that the claims should be understood to include modified forms of those embodiments, including portions of the embodiments and combinations of elements of different embodiments within the scope of the following claims. All publications described herein, including patent and non-patent publications, are incorporated herein by reference in their entirety.

[0061] To assist the Patent Office and any reader of any patent that may issue based upon this application in interpreting the appended claims, Applicants wish to call attention to the fact that they do not intend for any appended claim or claim element to invoke 35 U.S.C. § 112(f) unless the term “means for” or “step for” is expressly used in a particular claim.

[0062] The embodiments described herein explain the best mode known for practicing the invention and will enable others skilled in the art to utilize the invention.

Claims

1. A liquid level sensor, comprising: Long float; a sensor head provided with a sealed compartment, the sensor head being adapted to be received at an opening in an upper wall of the reservoir and provided with a downwardly extending guide for supporting the elongated float and allowing the elongated float to move below the sensor head along a vertical axis; a sensor mounted within the sealed compartment to sense the height of the elongated float relative to the sensor head; as well as a spring extending between the sensor head and the elongated float to bias the elongated float downward against a buoyancy force exerted on the elongated float, wherein the downwardly extending guide is a finger-like member having inwardly extending teeth for engaging an outwardly extending rim on the elongated float, and Wherein the outwardly extending rim and inwardly extending teeth have opposing inclined surfaces that provide an upward snap-fit ​​engagement as the float moves upward relative to the finger.

2. The liquid level sensor according to claim 1, wherein: When the elongated float is in the lowest engaged position, the inwardly extending teeth are in contact with the outwardly extending rim over less than 25% of the circumferential length of the rim.

3. The liquid level sensor according to claim 1, wherein: The elongated float extends a first distance below a lowest extension of the downwardly extending guide, the first distance being greater than a second distance above the lowest extension of the downwardly extending guide.

4. The liquid level sensor according to claim 1, wherein: The spring is a polymer material.

5. The liquid level sensor according to claim 1, wherein: The spring is mounted above a lowermost extension of the downwardly extending guide.

6. The liquid level sensor according to claim 1, wherein: The spring is a sheet of planar material having a spiral groove and a central opening, attached to the elongated float to extend perpendicular to the vertical axis, and having an outer periphery attached to a surrounding wall of the sensor head.

7. The liquid level sensor according to claim 6, wherein: The outer periphery is provided with radially extending tabs which are bent downwardly to pass upwardly through the lower edge of the surrounding wall and then bent outwardly to engage corresponding holes in the surrounding wall when aligned with the holes.

8. The liquid level sensor according to claim 7, wherein: The tabs engage the corresponding openings at relative locations between the elongated float and the sensor head prior to engagement between the downwardly extending guide and the elongated float.

9. The liquid level sensor according to claim 1, wherein: The sensor is an inductive sensor, and the upper portion of the elongated float is provided with an upwardly extending inductive element at the top of the elongated float.

10. The liquid level sensor according to claim 9, wherein: The sealed compartment includes an inwardly extending pocket for accommodating the upwardly extending inductive element.

11. The liquid level sensor according to claim 10, wherein: The inductive sensor is provided with an antenna formed as a spiral portion on an envelope of a printed circuit board having a hole fitted around the inwardly extending pocket.

12. The liquid level sensor according to claim 11, wherein: The spiral portion is formed at the bottom of the printed circuit board toward the elongated float.

13. The liquid level sensor according to claim 9, wherein: The inductor element is a ferrite element.

14. The liquid level sensor according to claim 1, wherein: The elongated float is a polymeric container having an enclosed air pocket sealed within the float and wherein the container has a constant cross-sectional area in a portion of the container extending below the downwardly extending guide.

15. The liquid level sensor of claim 1, further comprising the reservoir, wherein: The reservoir has fill height markings indicating a maximum fill level of the reservoir, and wherein the downwardly extending guide is above the fill height markings when the sensor head is mounted on the reservoir.

16. The liquid level sensor according to claim 1, wherein: The sensor head includes an O-ring for sealing the sensor head to the opening in the reservoir.

17. A liquid level sensor for determining the level of a liquid volume in an appliance reservoir, the liquid level sensor comprising: Long float; A sensor head, the sensor head being provided with a sealed compartment, wherein the sensor head: adapted to be received in an opening in an upper wall of a utensil reservoir; including a neck ring engaging the upper wall of the utensil reservoir to provide a sealing engagement between the neck ring and the upper wall of the utensil reservoir; A downwardly extending guide is provided for supporting the elongated float and allowing the elongated float to move along a vertical axis below the sensor head; a sensor mounted in the sealed compartment to sense the height of the elongated float relative to the sensor head; as well as a spring extending between the sensor head and the elongated float to bias the elongated float downward against a buoyancy force exerted on the elongated float, wherein the downwardly extending guide is a finger-like member having inwardly extending teeth for engaging an outwardly extending rim on the elongated float, and Wherein the outwardly extending rim and inwardly extending teeth have opposing inclined surfaces that provide an upward snap-fit ​​engagement as the float moves upward relative to the finger.

18. The liquid level sensor according to claim 17, wherein: The elongated float is defined by an elongated bottle having the outwardly extending rim.

Images