Geometrical instruments – Indicator of direction of force traversing natural media – Level or plumb – terrestrial gravitation responsive
Reexamination Certificate
2001-06-11
2003-09-30
Gutierrez, Diego (Department: 2859)
Geometrical instruments
Indicator of direction of force traversing natural media
Level or plumb, terrestrial gravitation responsive
C033S366110
Reexamination Certificate
active
06625896
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to tilt sensors, and more particularly to an electrolytic tilt sensor that is manufactured using standard printed circuit board fabrication techniques.
Traditional tilt sensors generally use some mechanism that is influenced by the local gravitational field in order to determine the level of tilt from some horizontal reference position. One type of sensor uses a weighted, rotating pendulum that is attached to a potentiometer or variable capacitor. Accuracy of this type of sensor is limited by the design and cost of the shaft and bearing about which the pendulum swings. For many applications, a pendulum type tilt sensor is too large, heavy, and expensive. A second type of tilt sensor measures the gravitational force on a conventional or micro-machined weighted beam. Although these types of tilt sensors can be small and relatively inexpensive, the electrical output varies as the sine/cosine of the tilt angle whereupon the relation between tilt angle and electrical output varies considerably throughout the range of the sensor. A third type of tilt sensor uses variations of the traditional “bubble level.” If the fluid in this type of sensor is electrically conductive, electrodes placed in contact with the fluid result in an electrical response related to the tilt angle. The changing electrical impedance between the contacts can be converted to a useable output with proper signal conditioning electronics.
Historically, most of these types of sensors have been hand assembled using precious metal electrode wires, glass housings, and lead wires that have been sealed and attached by hand. Thus, these types of sensors require skilled labor assembly, which tends to be costly. More recently, glass housed tilt sensors have been made by machine, which lowers their fabrication costs, but are only available in limited configurations. Even with lowered manufacturing costs, tilt sensors that have glass housings are very fragile and still expensive to mount in an instrument housing. Some manufacturers sell sensors mounted in machined metal housings. However, sensors mounted in metal housings are relatively expensive, and too large for many applications.
A need therefore exists for a tilt sensor that is inexpensive to manufacture, small, and easily mounted. A further need exists for a tilt sensor that can be mass produced with very repeatable performance characteristics.
SUMMARY OF THE INVENTION
The present invention provides an electrolytic tilt sensor that is manufactured using standard printed circuit board manufacturing techniques. An electrolytic tilt sensor manufactured in accordance with the methods of the present invention include an electrolytic sensing element that is electrically interconnected to a signal processing circuit that generates an electrical output signal that is functionally related to the angular displacement of the electrolytic sensing element with respect to a local gravitational field, such as that of the earth. An important advantage of the invention is that the circuitry for the electrolytic sensing element and signal processing circuit are manufactured on a single insulating substrate such as a printed circuit board using standard printed circuit board manufacturing techniques. Electrolytic tilt sensors manufactured in accordance with the present invention may be mass produced inexpensively and have excellent uniformity in their performance characteristic.
The electrolytic sensing element is manufactured by: a) forming first and second sensing electrodes on a generally planar surface of a dielectric substrate; b) forming a reference electrode on the generally planar surface; c) mounting a housing to the dielectric substrate so that the first and second sensing electrodes and the reference electrode are contiguous to a volume defined between the housing and the dielectric substrate; d) forming a fluid tight seal between the housing and the dielectric substrate; e) injecting an electrolytic fluid into the volume; f) sealing the electrolytic fluid in the volume; and g) forming an electrical circuit on the dielectric substrate for generating an output signal representing an angular position of the dielectric substrate with respect to a gravitational field. The electrical circuit is interconnected to the electrolytic sensor element by traces, also formed on the substrate.
The invention also provides an electrolytic tilt sensor that is fabricated on a single substrate such as a printed circuit board. An electrolytic tilt sensor, comprises: a) a dielectric substrate having a first planar surface; b) a first sensing electrode affixed to the dielectric substrate and having a second planar surface entirely in contact with the first planar surface; c) a second sensing electrode affixed to the dielectric substrate and having a third planar surface entirely in contact with the first planar surface; d) a reference electrode affixed to the dielectric substrate and having a fourth planar surface entirely in contact with the first planar surface; e) a housing mounted to the dielectric substrate so that the first and second sensing electrodes and the reference electrode are contiguous to a volume defined between the housing and the dielectric substrate; f) a fluid tight seal formed between the housing and the dielectric substrate; g) an electrolytic fluid contained within the volume; and h) electrical circuitry mounted on the dielectric substrate and electrically coupled to the first and second sensing electrodes, and to the reference electrode for generating an electrical signal representing an angular displacement of the electrolytic fluid with respect to the dielectric substrate.
An important advantage of the invention is that it provides a method for manufacturing tilt sensors having inexpensive unit costs, where the sensors have very uniform performance characteristics.
Another important advantage of the invention is that the tilt sensors may be directly fabricated on printed circuit boards using standard “step and repeat” processing. The inventive process allows new tilt sensor designs to be quickly implemented with a choice of electrode coatings and trace materials such as copper, gold, tin, and silver.
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Courson Tania C.
Gutierrez Diego
Kagan Michael A
Lipovsky Peter A.
The United States of America as represented by the Secretary of
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