Measuring and testing – Dynamometers – Responsive to force
Reexamination Certificate
1999-07-27
2001-01-16
Noori, Max (Department: 2855)
Measuring and testing
Dynamometers
Responsive to force
C073S772000
Reexamination Certificate
active
06173618
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method and apparatus for detecting fill level and blockages in ore passes and other vertical or near-vertical shafts.
Large commercial mining operations often involve mining several different ore bearing layers. The mined ore is delivered to trucks or the like in a main drive shaft located below the lowest ore bearing layer. Ore pass shafts are vertical or near-vertical shafts used to transport ore mined in the bearing layers down to the main drive shaft. The ore pass shafts can be from eight feet in diameter for cutout shafts and up to fifty feet in diameter for blasted out shafts. They run from fifty feet to two hundred feet in length, and in some occasion up to one thousand feet in length.
Ore passes, backfill raises, mine draw points, chutes and other near vertical raises frequently get blocked due to bridging material. Chutes and grain hoppers usually contain access panels for inspection of internal areas and are also relatively easily accessible outside. Ore passes are only accessible from the inside and present an extremely harsh environment. Because of this it is not easy to determine the location and source of the blockage.
Several methods exist for locating and detecting blockages in material handling systems. U.S. Pat. No. 5,063,729 to Fox et al. describes a cotton blockage detector for a harvester which uses an acoustic output directed toward the discharge door floor of the cotton picking unit. When the cotton picking unit is operating properly, the floor area is clear. When a blockage occurs, the area begins to fill with cotton and debris, causing a decrease in the monitored distance. U.S. Pat. No. 4,068,223 to R. Steffen describes a monitoring system for agricultural harvesting apparatus in which flow sensing means is mounted in a duct for the passage of the harvest. The apparatus senses changes in airflow, indicating when a blockage occurs. U.S. Pat. No. 4,546,346 to Wave et al. describes a sewer line backup detection, alarm and detention apparatus include a series of pneumatic switches coupled to a pressure sensitive diaphragms extending into the sewer at various locations. In the event of a sewer blockage, the blocked material exerts pressure on the diaphragm which closes the switch. None of these techniques is suitable for the rough environment of an ore pass.
Many bulk material level indicators are currently in use. The most common technologies involve the use of radio frequency (RF) and laser beams. A major disadvantage of these technologies is that they require an external mounting arrangement. Ore passes require an internal mounting arrangement since only the internal walls can be accessed.
Once a blockage is determined, the ore pass must be unblocked. Several techniques exist for unblocking ore passes and other near-vertical shafts: running water, boring and in extreme cases, explosives. While it is important for safety and productivity reasons to unblock the ore pass, it is also important to be able to locate the blockage areas quickly and efficiently. Knowledge of the extent and location of the blockage can also help determine the type and safest method for clearing it.
There is a need for an apparatus for detecting level and locating blockages in the rugged environment of an ore pass. There is a need for a low cost and easily installed level detector and blockage locator. There is a further need for a level detector and blockage locator which can withstand most non-explosive cleanout techniques. There is a need for a level detector and blockage locator which can be installed on the internal walls of an ore pass or other vertical rise.
SUMMARY OF THE INVENTION
To achieve the foregoing and other objects, a method of, and apparatus for, locating a blockage in an ore pass or other near-vertical shaft is described. The level and blockage detector includes a flexible metal strip in which a plurality of strain detectors or gages have been located, spaced apart from one another, preferably at known distances. A plurality of anchors secure the metal strip to the interior surface of the shaft such that the metal strip is displaced a fixed distance from the interior surface. The anchors are located intermediate to the strain detectors. The anchors prevent movement of the strip except between the anchors. Thus maximum deflection occurs at the center of the portion of the strip, at the location of the strain detector.
When the ore pass fills up with bulk material, the bulk material causes the metal strip to deflect toward the interior surface of the shaft. This causes the resistance of the strain detector in the region of the deflection to change.
To detect the location of the blockage or level of the bulk material, a microcontroller cycles through each strain gage, placing it as the fourth arm of a bridge circuit. When a change in the output voltage across the bridge circuit is detected, caused by a change in resistance of the strain detector, the location of the blockage can be determined. The level of tolerance of the location is somewhere in the range of the distance between the strain detectors. For example, referring to
FIG. 1A
, if a change in output voltage is detected at strain detector
1
and
2
, but not at number
3
or
4
, then the blockage is at or slightly below the location of strain detector
2
.
Once the location of the blockage is determined, a display consisting of a series of light emitting diodes, (LED), one for each strain gage can be coupled to the bridge circuit. When a change in output voltage is detected across the bridge circuit, current is applied to the LED for that strain detector, causing it to light. Other means of displaying the location of the blockage or level may also be used. For example, CRT or LCD display may provide software driven data indicating the location of the blockage.
Preferably, the strain detectors and wiring are located on the inside surface of the metal strap or strip. This will prevent damage from the bulk material as it falls past the metal strap. Preferably, steel strapping may be used. Steel strapping of a thickness of at least about one eighth inch and width of about five inches provides sufficient rigidity and deformability to enable the strain detectors to be deflected during when material is present, but not during normal fall of the bulk material. The distance the metal strap is located from the interior surface of the shaft, as well as the dimensions of the metal strap, will vary depending on the type of bulk material. Occurrence of a blockage or a full ore pass should not, preferably, permanently deform the metal strap in the region of the blockage. However, if the strap is deformed permanently, the system can be recalibrated to zero out the deformation.
The system is comprised of relatively inexpensive components and can be easily installed in an ore pass. Run lengths of up to 200 feet of metal strap are possible without loss of signal strength. For longer shafts, multiple blockage locators can be installed.
REFERENCES:
patent: 3868662 (1975-02-01), Russell Jr.
patent: 4068223 (1978-01-01), Steffen
patent: 4138898 (1979-02-01), Watts et al.
patent: 4546346 (1985-10-01), Wave et al.
patent: 4813320 (1989-03-01), Malloy et al.
patent: 5063729 (1991-11-01), Fox et al.
patent: 5922967 (1999-07-01), Motoyama
Fitch Even Tabin & Flannery
Noori Max
The United States of America as represented by the Department of
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