Measuring and testing – Sampler – sample handling – etc. – Capture device
Reexamination Certificate
2001-08-22
2003-02-18
Williams, Hezron (Department: 2856)
Measuring and testing
Sampler, sample handling, etc.
Capture device
C073S863000, C073S863560, C073S864910
Reexamination Certificate
active
06520035
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to bulk material sampling systems and more particularly, to systems for extracting samples of bulk material from a moving conveyor belt.
Bulk material such as particulate coal or ore that is transported in a continuous stream by a belt conveyor is often the subject of cross-stream sampling. The usual objective of such cross-stream sampling is the characterization of certain material properties for the purposes of quality and value determination. The quality and character of a material sample frequently determines the value or use of that material deposited along the belt within a reasonable proximity of the sample. Consequently the statistical accuracy of sample representation is extremely important.
One example of equipment for extracting a material sample from the moving surface of a belt conveyor comprises a rotating sample cutter that is positioned to be driven about a rotational path that crosses the conveyor belt path. As the cutter transversely engages the material stream carried by the moving belt, that segment of material in the belt stream located between the rotational planes of the cutter side walls is swept or scooped into the cutter bin and becomes the sample increment.
As a general principle, the more rapidly the cutter passes through the material flow stream, the more accurate and reliable is the sample representation. The specification of U.S. Pat. No. 5,767,421, the disclosure of which is hereby incorporated by reference, describes the mechanics of how a rapidly moving cutter extracts a more complete and valuable representation of the material carried by the belt.
An independent incentive for greater cutter speed is the mathematical interrelationship between the width of the cutter opening, the material particle size and the belt speed. This interrelationship is described with respect to
FIGS. 1A through 1C
and is predicated on an empirical principle of statistical sampling that the effective cutter opening width, i.e. measured parallel with the belt traveling direction, should be between 2.5 to 3 times the width of the largest particle in the loose agglomeration of material particles that are the subject of the sample.
FIG. 1A
represents an increment of particulate material
10
deposited in an elongated pile on a stationary carrier belt
12
. The material extraction swath
14
a
is that width of material removed from the elongated pile by passage of the cutter through the pile. The rotational planes
16
a
and
16
b
respective to the cutter sidewalls define the maximum width dimension of the swath
14
a.
If the width of swath
14
a
is 3 times greater than the effective diameter of the largest particle in the material pile
10
when the belt is stationary as represented by
FIG. 1A
, the normal width of swath
14
b
is reduced to 2.57 times the particle diameter when the cutter, moving at 1000 ft/min, traverses a belt
12
moving at 600 ft/min as illustrated by FIG.
1
B. The normal motion vectors define a resultant angle of 59° between the cutter side planes
16
a
and
16
b
and the belt traveling direction. This 59° resultant angle reduces the normal width of the swath
14
b
to only 2.57 times the particle diameter.
FIG. 1C
shows that for the same cutter moving at a speed of 700 ft/min traversing the belt moving at 1000 ft/min, the resultant vector angle is 35° and the normal swath width
14
c
is only 1.72 times the particle size: an unacceptably low ratio.
Larger rotary belt samplers are usually driven by a pair of double-acting pneumatic cylinders. The cutter structure is secured for 360° rotation about an axis or axle shaft. The axle shaft passes through two bearing supports. The cutter rotates in a swath between the supports. Outside of the cutter rotational swath, usually on opposite sides of the cutter swath, are a pair of crank throws radiating from the cutter axle shaft. The crank throws are structurally rigid with the axle shaft and cutter and angularly offset about the axle shaft axis whereby one rotatively leads the other about the axle shaft axis by about 20° to 50°; usually about 40°. Each of these crank throws is pivotally connected to the rod end of a respective double-acting, single rod cylinder. The bore end of the cylinder unit usually is pivotally secured to a stationary axis aligned substantially parallel with the cutter rotational axis.
Characteristic of a double-acting cylinder is the use of pressurized fluid, i.e. air, on both sides of a piston that is structurally secured to a rod. Consequently, the cylinder has two pressure chambers. In those machines having the rod projecting from only one side of the piston, i.e. a single rod cylinder, these two chambers may be further distinguished as the head chamber and the rod chamber. This distinction is significant due to respectively different working areas and volumes. The working area and volume of the rod chamber is less than that of the head chamber by the area and volume of the rod that is stroked by displacement of the piston along the cylinder bore. The operative result of these distinctions is that greater fluid pressure is required in the rod chamber than the head chamber to produce the same rod force. However, more fluid volume is required in the head chamber than the rod chamber to produce the same rod displacement distance. Due to the many characteristics of a compressible fluid that effect the mass, density and flow rate across an orifice or through a port aperture, the optimum valve timing for opening and closing fluid flow ports respective to the head and rod chambers of a double acting cylinder is different.
Valve timing is generally referenced to the physical position of the piston within the cylinder bore when fluid is admitted to or released from a chamber. For example, when the rod is extended from the cylinder to the maximum, the piston position may be characterized as the upper dead center position. The opposite extreme, when the rod is drawn into the cylinder to the maximum degree, is characterized as the lower dead center position. Intermediate positions are characterized as before or after a center (upper or lower) position. If the outer end of the rod is connected to a crank throw, such intermediate positions may be designated in terms of crank rotational degrees.
Traditionally, fluid flow respective to the two chambers of a double-acting cylinder that drives a crank throw about a full 360° rotation is controlled by a single “4-way valve”. The “4-way” reference is to the number of conduit connection ports in the valve body. Two ports are dedicated to the fluid flow respective to the two pressure chambers in the cylinder. One valve port is dedicated to the fluid pressure supply and the fourth valve port is dedicated to the spent fluid discharge e.g. atmosphere. Operation of the valve “spool” connects the pressure supply alternately with the rod chamber and the head chamber. Simultaneously, when the rod chamber is connected with the fluid supply, the head chamber is connected with the fluid discharge. No relative timing in the sequence of these four events is possible. The usual prior art practice, for example, is to switch the 4-way valve spool when the piston reaches upper dead center and switch again when the piston reaches lower dead center.
The consequence of an invariant prior art valve sequence is exacerbated by the structural fact that all working fluid must pass through the same 4-way valve twice in a rod stroke cycle. In effect, the fluid flow port of each chamber is as long as the respective conduit that connects the 4-way valve. The volume of each chamber is increased accordingly. Hence, when the valve spool shifts, pressurized fluid must first negate the inertia of the out flowing fluid to begin the fluid inflow. Sufficient fluid must thereafter enter the chamber flow port conduit to raise the pressure along the conduit before any force is transferred to the piston face. Simultaneously, when the valve spool opens a conduit to atmosphere, the pressure in the conduit, when opened, is at
Long Armistead M.
Long John B.
Heron Holdings
Luedeka Neely & Graham P.C.
Williams Hezron
Wilson Katina
LandOfFree
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