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Method of sensing tilt, tilt sensor, and method of manufacturing sameRelated Patent Categories: Geometrical Instruments, Indicator Of Direction Of Force Traversing Natural Media, Level Or Plumb, Terrestrial Gravitation Responsive, Electrically Actuated Signal Or Indicator, Fluent Sensor, Having Resistive Or Contact Circuit Control ElementMethod of sensing tilt, tilt sensor, and method of manufacturing same description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060213070, Method of sensing tilt, tilt sensor, and method of manufacturing same. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates generally to tilt sensors. More particularly, the present invention relates to a low-cost, high-volume electrolytic tilt sensor. [0003] 2. Description of the Related Art [0004] Electrolytic tilt sensors are devices that provide output signals proportional to the angle or direction of tilt in conjunction with a corresponding electrical circuit. Tilt sensors were originally used in weapons delivery and aircraft navigation, but are now used in a wide variety of applications, such as drilling, laser guidance, automotive wheel alignment, geophysical monitoring, virtual reality, and robotic systems. [0005] Disadvantages commonly associated with conventional electrolytic tilt sensors include difficulties in manufacturing the sensor. Moreover, sensor manufacture requires a significant degree of skill, fixturing, labor-intensive handwork, and art by highly trained operators to achieve the desired parameters. In addition, tolerances of the glass housing during its processing can vary greatly, which results in either a higher reject rate and/or a greater range of mechanical and electrical tolerances in the end product. Further, tilt sensor components are relatively fragile due to their construction and must be handled with extreme caution. [0006] With respect to glass electrolytic tilt sensors, great care must be afforded to the thermal and mechanical stress related characteristics of the glass during installation and alignment. This significantly limits the range of application of such sensors. [0007] Conventional electrolytic tilt sensors also typically incorporate precious metal electrodes, which are sealed and attached by hand and account for a majority of the manufacturing cost of the completed sensor. Thus, the cost of manufacturing tilt sensors is substantially proportional to the number of electrodes required for each sensor. [0008] Therefore, there is a need in the prior art for an electrolytic tilt sensor that is small, lightweight, rugged, simple, inexpensive to manufacture, applicable by various automated mounting processes, and requires fewer electrodes than conventional sensors. The need also exists for a tilt sensor that is readily adaptable to mass production techniques within acceptable tolerances. SUMMARY OF THE INVENTION [0009] The present invention, which addresses the needs of the prior art, relates to a method of sensing tilt, which includes applying an electrical signal to at least one electrode of a first set of spaced-apart electrodes and measuring a first electrical parameter using at least one electrode of a second set of spaced-apart electrodes. The first and second sets of electrodes are disposed in a conductive medium and the conductive medium is disposed in an envelope. The first electrical parameter is responsive to the applied electrical signal and represents an angle of tilt relative to a first axis, such that no more than four electrodes provide electrical parameters representative of angles of tilt relative to two non-parallel axes. The electrical signal can be applied in the form of a voltage or a current and can be applied as a continuous or time-varying signal, such as but not limited to an alternating current (ac) or direct current (dc) signal. [0010] The electrical roles of the first and second sets of electrodes may be reversed to include applying an electrical signal to at least one electrode of the second set of electrodes, and measuring a second electrical parameter using at least one electrode of the first set of electrodes. The second electrical parameter is responsive to the applied electrical signal and represents an angle of tilt relative to a second axis. [0011] The first set of electrodes and the second set of electrodes may be positioned such that the first axis is substantially non-parallel with the second axis, and the spacing between the first set of electrodes is equal to the spacing separating the second set of electrodes. The first electrical parameter may include at least one of voltage, current, resistance, capacitance, impedance, and inductance, and the first and second sets of electrodes each preferably include two electrodes. [0012] The present invention further relates to a method of sensing tilt relative to a plurality of axes, which may include measuring the first electrical parameter from a first electrode, measuring the first electrical parameter from a second electrode, and combining the first electrical parameter measured from the first electrode and the second electrode. The combined first electrical parameter represents the angle of tilt relative to the first axis. [0013] The present invention still further relates to a tilt sensor, which includes an envelope, a conductive medium disposed in the envelope in an amount adapted to provide a free liquid surface, and at least four electrodes disposed in the envelope such that a portion of each electrode is in contact with the conductive medium. The electrodes are electrically insulated from each other to provide at least a first set of spaced-apart electrodes and at least a second set of spaced-apart electrodes. [0014] At least one electrode of at least one of the first set of electrodes and the second set of electrodes is adapted to be selectively connected to an electrical source such that an electrical signal is applied thereto. At least one electrode of at least one of the first set of electrodes and the second set of electrodes is adapted to be used to provide an electrical parameter in response to the applied electrical signal, wherein the electrical parameter is representative of an angle of tilt relative to at least one axis. No more than four electrodes provide electrical parameters representative of angles of tilt relative to two non-parallel axes. [0015] The first set of electrodes defines a first axis, the second set of electrodes defines a second axis, and the first axis is substantially non-parallel with the second axis. The electrodes in each set of electrodes are disposed on substantially opposing sides of a non-conductive projection or envelope, and the tilt sensor preferably includes four electrodes. [0016] The present invention yet further relates to a tilt sensing system, which includes the tilt sensor, an electrical source adapted to be connected to at least one electrode of at least one of the first set of electrodes and the second set of electrodes such that an electrical signal is applied thereto. The system may include one or more mixers adapted to combine at least one of the first electrical parameter and the second electrical parameter. The mixer is adapted to provide a tilt parameter representing an angle of tilt relative to at least one axis. [0017] The electrical source may include a first signal generator and a second signal generator adapted to be connected to electrodes disposed on opposing sides of the non-conductive projection. The system may include amplifiers and three-state drivers. [0018] The present invention still further relates to a method of making a tilt sensor, which includes providing at least four electrodes, forming an envelope adapted to receive at least a portion of the electrodes, placing a conductive medium into the envelope, and sealing the conductive medium in the envelope to be in contact with at least a portion of each electrode. The electrodes include at least two sets of spaced-apart electrodes, such that no more than four electrodes provide electrical parameters representative of angles of tilt relative to two non-parallel axes. [0019] The electrodes may be formed on an electrode stud or an inner surface of the envelope. The electrode stud may include a plurality of spaced-apart longitudinal slots, in which the electrodes are disposed. The envelope may be adapted to receive at least a portion of a header disk, and the method may include forming the header disk to include an aperture adapted to receive the electrode stud, inserting the electrode stud in the aperture of the header disk, and inserting the header disk in the aperture of the envelope. [0020] The method may also include forming a seal, which can be a poured or preformed seal made from epoxy or other known sealant material, around the electrode stud in the aperture of the header disk, and applying the seal around the electrode stud in the aperture of the header disk. Sealing the conductive medium in the envelope may include curing the seal. [0021] The method may also include forming a molded header including the electrode stud and the header disk integral therewith. The molded header may include spaced-apart slots extending through apertures in the header disk, or spaced-apart slots substantially aligned with spaced-apart slots disposed on an exterior surface of the header disk. The envelope, electrode stud, header disk, seal, and molded header may include at least one of polyphenyleneoxide (PPO.RTM.) resin, polypropylene, Vectra.RTM., Peak.RTM., Ultem.RTM., or the like and epoxy. [0022] At least two of the envelope, electrode stud, header disk, seal, and molded header may have substantially the same temperature coefficient of expansion. The envelope may include a raised boss with an aperture therethrough, and the method may include applying the conductive medium through the aperture in the raised boss, and sealing the aperture in the raised boss. Continue reading about Method of sensing tilt, tilt sensor, and method of manufacturing same... 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