Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
2000-06-13
2002-11-26
Le, N. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S678000, C324S658000, C324S686000, C324S688000
Reexamination Certificate
active
06486680
ABSTRACT:
The present invention relates to a device for measuring capacitance, and more particularly to a device to detect the edge of materials, and even more particularly, to a device for the contactless detection of a moving web of material.
INCORPORATION BY REFERENCE
U.S. Pat. Nos. 5,394,095 and 5,767,686 describe and illustrate devices that detect the edge of conductive materials and control the position of the conductive materials relative to the detector of the type to which the present invention is directed. These patents are incorporated by reference herein as background information to explain certain prior edge detection and web position control arrangements of which the present invention is a specific improvement. Consequently, the details of the conductive material and the positioning of the conductive material to which the present invention is directed need not be explained in detail.
BACKGROUND OF THE INVENTION
The present invention pertains to a device to detect the capacitance between two or more electrodes as a material is positioned between the electrodes, and more particularly to an edge detector for contactless detection of the position of a moving web of conductive material and will be described with particular reference thereto; however, the invention has broader applications and can be used in any type of application which requires the accurate detection of capacitance between two or more electrodes.
Edge detectors are commonly used in conjunction with apparatus that process moving webs of material. The edge detector is used to properly align the moving web of material in the apparatus. Several types of mechanical and electronic devices have been used to detect and/or control the position of the web of material. Some of these devices are disclosed in U.S. Pat. Nos. 5,394,095 and 5,767,686. In these prior art devices, the lateral position of the web of conductive material is detected by positioning two or more detector electrodes in the area of each lateral edge of the conductive material. The capacitance between the electrodes at each lateral edge of the conductive material is measured and then used to control the lateral position of the conductive material. The lateral movement of the conductive material between the electrodes causes changes in the coupling fields between the electrodes, thereby increasing or decreasing the capacitance between the electrodes. The measured capacitance is used to determine the position of the edge of the conductive material relative to the electrodes, and such determined position is used to control the lateral position of the conductive material. The electrodes are typically shielded to isolate the electrodes from external electrical interference so as to improve the accuracy of the measured capacitance.
Although these devices satisfactorily measure the capacitance between the electrodes to determine the position of the edge of the conductive material relative to the electrodes, these devices are expensive and complex to manufacture, are very sensitive to external electrical interferences, and are unable to account for parasitic charges in the measuring circuit, which parasitic charges can adversely affect the accuracy of the edge measurement and cause undesired drift in the position control of the conductive material.
In view of the present art of capacitance measuring devices for the detection and the position control of the edge of a conductive material, there is a need for a device that accurately measures the capacitance between two or more electrodes, is less sensitive to external electrical interference, and reduces or overcomes the drift in the device.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a capacitance measuring circuit which is designed to measure the capacitance between a sensor electrode and a reference electrode. The capacitance measuring circuit can be used in many different types of applications where it is desired to accurately measure capacitance between two or more electrodes. The capacitance measuring circuit has particular applicability for use in detecting an edge of a conductive material, and will be particularly described with reference thereto; however, the capacitance measuring circuit can be used to measure the edge of a non-conductive material. The sensor electrode and the reference electrode of the capacitance measuring circuit are spaced apart from one another a sufficient distance so that an edge of a material can pass there between. Typically, the sensor electrode and the reference electrode are symmetrically oriented about a central axis that runs between the electrodes; however, it is not necessary that the electrode be symmetrically oriented with respect to one another. The capacitance measuring circuit includes or is designed to be connected to a first polarity voltage source and a second polarity voltage source. The first and second polarity voltage sources are used to electrically charge the sensor electrode and/or reference electrode. The capacitance measuring circuit also includes a capacitor which is used to fully or partially store a charge that is fully or partially representative of the capacitance between the sensor electrode and the reference electrode. The capacitance measuring circuit further includes a switch controller to electrically connect and/or disconnect the reference electrode, the sensor electrode, the first and second polarity voltage sources and/or the capacitor to or from one another. This sequence of operations by the switch controller to measure the capacitance between the reference electrode and sensor electrode is termed the capacitance measuring sequence. The term “electrically connected” as used in this application refers to an electrical connection that allows current and/or voltage to pass between two or more components in an electrical circuit. The term is not to be interpreted as requiring two or more components to be directly connected, thus two or more “electrically connected” components can be directly electrically connected or indirectly electrically connected. Two or more components that are indirectly electrically connected include one or more electrical elements connected between the two or more components. These electrical elements include, but are not limited to, resistors, inductors, capacitors, amplifiers, microprocessors, diodes and the like.
In accordance with one aspect of the present invention, the first polarity voltage source is a positive voltage source and the second polarity voltage source is a negative voltage source. The first polarity voltage source and the second polarity voltage source can be provided by one or more voltage sources. In one embodiment, the voltage source is a D.C. voltage source. In another embodiment, the voltage source is a rectified A.C. source. In yet another embodiment, the magnitude of the first polarity voltage source and the second polarity voltage source are generally equal. When the magnitude of the voltage sources are equal, the resulting charge on the capacitor during each measurement sequence actually or nearly represents the actual capacitance between the sensor electrode and the reference electrode. However, different magnitude voltage sources can be used. When different magnitude voltage sources are used, the charge on the capacitor during each measurement cycle will represent a relative capacitance. This relative capacitance can be used to control the position of the material or be converted to an actual capacitance prior to being used to control the positioning of the material.
In accordance with another aspect of the present invention, the conductive material is a web of material having a generally constant width and two lateral edges. At least one of the lateral edges of the material is oriented to be at least partially positioned between the sensor electrode and reference electrode. The material is made of a material to cause an interference in the electrical field between the sensor electrode and the reference electrode when a voltage is applied to the s
Fay Sharpe Fagan Minnich & McKee
Le N.
Sundaram T. R
The North American Manufacturing Company
LandOfFree
Edge detector does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Edge detector, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Edge detector will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2954448