Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – For fault location
Reexamination Certificate
1999-10-21
2001-10-23
Brown, Glenn W. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
For fault location
C324S532000, C324S633000, C324S637000, C324S634000, C324S071100
Reexamination Certificate
active
06307380
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to measurement of long distance or position such as measuring the traveling range of a frame of a truck crane, the position of a cylinder rod, the position of a carriage used in a vertical parking lot or an automated warehouse, the position of a container carrier, or the position of a top-running crane, and such as in a detector-equipped pneumatic cylinder or a tank liquid level meter.
2. Description of the Prior Art
There have been known some conventional methods of measuring a long distance; for example, a method using a radar or a laser beam, a technique for measuring the number of windings of a wire over a reel in which a winding detector is installed and also the angle of the winding to determine a position, and a technique for measuring the angle and the number of revolutions of a wheel which is equipped with a revolution detector and urged against a rail or the like to calculate the distance.
Such conventional distance measuring methods have disadvantages. More particularly, the accuracy of a radar method and a laser beam method may largely be affected by local climate such as sunlight levels or raining. In the method using a wire and a reel, the winding length per revolution of the wire may be varied due to change in the winding radius or rough winding. The method using a rail and a wheel may cause the wheel to slip and change its number of revolutions resulting in measurement error and in addition, its measuring of the revolution involves repeat (incremental counting) of the signal at each revolution hence requiring resetting of the origin when the measuring apparatus has been switched off and started again. Therefore, those will be less reliable in the continuous operation in any factory automated application or outdoor use.
SUMMARY OF THE INVENTION
An object of the present invention is thus to provide a distance measuring apparatus which is based on improved physical characteristics allowing the measurement of long distance to be carried out in absolute (not incremental) units and its accuracy to be hardly declined by any environmental change such as raining climate or temperature change.
For achievement of the foregoing object, a distance measuring apparatus according to the present invention is featured by concerning that the propagation speed of voltage across a conductor is stable regardless of a change in the external environmental conditions and measuring the propagating time of the voltage to calculate a distance.
The propagation speed of voltage across a conductor depends on the material of the conductor and generally is very high. With a conductor, e.g. a copper wire, where the propagation speed of voltage is substantially 1 meter per 5 nanoseconds (ns), a high-speed counter having a resolution time of more than 0.05 ns is needed for obtaining a resolution distance of 1 cm.
The present invention is directed to a distance measuring principle for measuring a distance at higher repeatability, a mechanical means for precisely pointing a target, and an electrical means for measuring such a high-speed event.
Assuming that a parallel conductor in an equivalent circuit shown in
FIG. 1
is arranged in an equivalent state where the inductance is L, the resistance is R, and the capacitance is C, the introduction of a pulse at one end of the parallel conductor causes its voltage to propagate forward throughout the parallel conductor and after reaching at the other end, to be reflected back to the introduced end.
A change in the voltage is induced by the reflection depending on the condition of joint at the other end. Also, when an impedance mismatch such as shown in
FIGS. 2-A
,
2
-B,
2
-C, or
2
-D occurs in the conductor, the voltage is reflected at the impedance mismatching point.
It is also assumed that the reflected wave received initially is a primary reflected wave and a reflection of the reflected wave on the introduced end where the voltage is inverted is a secondary reflected wave. The duration of time from the introduction of a pulse to the receipt of the primary reflected wave is determined by the propagation speed of voltage across the conductor and hardly affected by any external environmental change.
For mechanically imposing an impedance mismatch from the outside, a structure comprising one or some of the resistance R, the inductance L, and the capacitance C is provided and exposed adjacent to or directly on an intermediate portion of the parallel conductor.
Because a high-speed counter having a bulky construction is needed for measuring at a high resolution level the duration of time from the introduction of pulse to the receipt of the primary reflected wave, it is provided in the form of a high-speed analog circuit according to the present invention which is simple in the construction and high in the reliability for measuring the time.
Also, since the rise time of the voltage at the pulse introduction directly affects the measurement of a distance, a mechanical scheme for eliminating such drawback is provided.
The apparatus of the present invention permits the parallel conductor(s) to be arbitrarily bent for measuring the distance by means of reflection in a closed space such as the parallel conductor but not in an open space such as with the radar, is based on the propagation speed of voltage across the parallel conductor for measuring the distance hence having minimum interruption from external disturbance, and uses the known conductor for finding the propagation speed of voltage thus allowing absolute position measurement. Therefore, when two parallel conductors which are located at the same distance and different in material are compared, their materials can be classified separately by examining a difference between their propagation speeds.
The apparatus of the present invention converts the time into voltages without the use of a high-speed counter hence permitting very high speed processing of the time at a short distance or measurement of the distance and when employs a flexible conductor(s), enables to measure an object which is bent or has a curvature and can thus be used in a factory automation application of not conventional, new type.
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Jong et al., Time-Domain Characterization of Interconnect Discontinuities in High-Speed Circuits, IEEE Transaction on Components 1992.*
Burkhart et al., Arbitrary Pulse Shape Synthesis via Nonuniform Transmission Lines, IEEE Transaction on Microwaves 1990.
Hirai Eiichi
Miki Masayuki
Oshie Naomasa
Toda Seiji
Brown Glenn W.
Hamdan Wasseem H.
Jordan and Hamburg LLP
Levex Corporation
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