Fuzzy Evaluation of stream sample reability
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Fuzzy Evaluation of stream sample reability


DisciplinaProcessamento de Minerais I211 materiais2.062 seguidores
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Manual
The electric drive is the only drive likely to achieve constant speed of
the cutter across a flowing stream of particulate material (Pitard 1993).
3.3. Cutter Layout
Idle positions of the cutter should be outside the stream to permit the
motor to accelerate to its cruising speed before the cutter attains the
stream. When one idle position of the cutter is in the stream, as displayed
in Figure 4, a part of the stream enters the cutter all the time. The shaded
area illustrates the material that is collected but does not belong to the
increment. This situation is incorrect.
FUZZY EVALUATION OF STREAM SAMPLE RELIABILITY 285
In addition, the stream should fall exactly in the center of the cutter.
When the stream thickness is larger than the cutter length, the cutter lay-
out is incorrect. Hence, a part of the stream falls outside the cutter tra-
jectory, as shown in Figure 5. The shaded area illustrates the material
belonging to the increment that is not collected.
Furthermore, the minimum vertical distance u (see Figure 6)
between the liberation point of the stream and the plane described by
the cutter edges during sampling should be respected (Pitard 1993). This
prevents accidental obstruction between the cutter and the point of dis-
charge of the stream.
3.4. Cutter Path. The condition of cutter path correctness is that the
cutter path is perpendicular to the direction of the stream. For instance,
Figure 4. Incorrect cutter layout with idle position in the stream.
Figure 5. Incorrect cutter layout with stream thickness larger than cutter length.
286 C. KETATA AND M. C. ROCKWELL
if the cutter path is parallel to the stream direction, the sampling
operation is considered to be performed by the scheme: taking part of
the stream all of the time. This is always incorrect and is illustrated in
Figure 7. The shaded area represents the material collected by the cutter.
4. FUZZY SETS
The following fuzzy sets correspond to the sampling factors\u2019 reliability.
These fuzzy sets depend on the sampling situation characteristics such
as material heterogeneity.
Figure 6. Vertical distance u between the liberation point of the stream and the plane
described by the cutter edges.
Figure 7. Incorrect cutter path with taking part of the stream all of the time.
FUZZY EVALUATION OF STREAM SAMPLE RELIABILITY 287
4.1. Cutter Geometry
Here, the cutter is assumed to be resistant to violent impact of large frag-
ments. In this way, the cutter geometry becomes incorrect if it is
obstructed by sticky material such as fines. Figure 8 illustrates an
example of possible membership function of the fuzzy set \u2018\u2018very reliable
cutter geometry\u2019\u2019:
eAA ¼ \u2018\u2018very reliable cutter geometry\u2019\u2019 ¼ fðv; l ~AAðvÞÞjv 2 ½0; 1\ufffdg ð1Þ
In this expression, v denotes the area fraction of the cutter opening
given by:
v ¼ AE
A
ð2Þ
where AE represents the effective cutter area and A is the total cutter area
as shown in Figure 3.
The corresponding membership function equals:
leAAðvÞ ¼ v; 0 \ufffd v \ufffd 1 ð3Þ
4.2. Cutter Speed
The faulty cutter speed results when the cutter speed is not constant dur-
ing sampling. Figure 9 exhibits an example of possible membership func-
tion of the fuzzy set \u2018\u2018very reliable cutter speed\u2019\u2019:
eBB ¼ \u2018\u2018very reliable cutter speed ¼ fðx;leBðxÞÞjx 2 ½0; 1\ufffdg ð4Þ
Figure 8. Example of fuzzy set \u2018\u2018very reliable cutter geometry.\u2019\u2019
288 C. KETATA AND M. C. ROCKWELL
where x is the constant-speed length fraction of the cutter given by:
x ¼ LA
LT
ð5Þ
where LA symbolizes the actual cutter path length that is perpendicular
to the stream direction and equal to the length of constant speed and LT
is the stream width. The corresponding membership function is:
leBðxÞ ¼ x; 0 \ufffd x \ufffd 1 ð6Þ
4.3. Cutter Layout
Here, the minimum vertical distance u, which prevents accidental
obstruction between the cutter and the point of stream discharge, is
assumed to be respected. In addition, the cutter is presumed to have
its idle positions completely outside the flowing stream. Thus, the faulty
layout results when the stream thickness is larger than the cutter length.
Figure 10 displays an example of possible membership function of the
fuzzy set \u2018\u2018very reliable cutter layout\u2019\u2019:
eCC ¼ \u2018\u2018very reliable cutter layout\u2019\u2019 ¼ fðy; leCðyÞÞjy 2 ½0;þ1\ufffdg ð7Þ
where y is the cutter length fraction given by:
y ¼ L
l
ð8Þ
Figure 9. Example of fuzzy set \u2018\u2018very reliable cutter speed.\u2019\u2019
FUZZY EVALUATION OF STREAM SAMPLE RELIABILITY 289
where L and l represent the stream thickness and the cutter length,
respectively (see Figure 5). The related membership function is written as
leCðyÞ ¼ 1; 0 \ufffd y \ufffd 11=y; y \ufffd 1
\ufffd
ð9Þ
4.4. Cutter Path
The incorrect cutter path results when the cutter deviates from the cor-
rect route that is perpendicular to the stream direction. Figure 11 shows
an example of possible membership function of the fuzzy set \u2018\u2018very
Figure 10. Example of fuzzy set \u2018\u2018very reliable cutter layout.\u2019\u2019
Figure 11. Example of fuzzy set \u2018\u2018very reliable cutter path.\u2019\u2019
290 C. KETATA AND M. C. ROCKWELL
reliable cutter path\u2019\u2019:
eDD ¼ \u2018\u2018very reliable cutter path\u2019\u2019 ¼ fðz; leDðzÞÞjz 2 ½0\ufffd; 90\ufffd\ufffdg ð10Þ
where z is the cutter deviation angle, in degrees, from the correct cutter
path that is perpendicular to the stream (see Figure 7). The related mem-
bership function is described by:
leDðzÞ ¼ cosðzÞ; 0 \ufffd z \ufffd 90\ufffd ð11Þ
5. FUZZY EVALUATION OF SAMPLE RELIABILITY
The sample reliability is assumed to be influenced by the sampling
factors:
1) Cutter geometry
2) Cutter Speed
3) Cutter layout
4) Cutter path
To assess the sample reliability, the compound influence of the
sampling factors should be evaluated. This situation is essentially a
multi-criterion decision-making problem.
The sampling factors are put into the set C:
C ¼ ½cutter geometry, cutter speed, cutter layout, cutter path\ufffd: ð12Þ
The sample reliability is described by five indexes, namely very
reliable, r1; reliable, r2; adequate, r3; doubtful, r4; and very doubtful, r5.
These indexes are represented by index set R:
R ¼ ½r1; r2; r3; r4; r5\ufffd ð13Þ
Thus, the fuzzy relation eRR is established:
eRR ¼ \u2018\u2018 ci is rj \u2019\u2019 ð14Þ
where i ¼ 1; . . . ; 4 and j ¼ 1; . . . ; 5.
Then, eRR is defined by the matrix:
eRR ¼
r11 r12 r13 r14 r15
r21 r22 r23 r24 r25
r31 r32 r33 r34 r35
r41 r42 r43 r44 r45
2
664
3
775 ð15Þ
FUZZY EVALUATION OF STREAM SAMPLE RELIABILITY 291
where rij 2 ½0; 1\ufffd is the membership grade of the pair (ci,rj) given by:
rij ¼ leRðci; rjÞ: ð16Þ
Now, the degree of sampling factor importance is represented by the
fuzzy set eII :
eII ¼ ½i1; i2; i3; i4\ufffd ð17Þ
where ik is the membership grade of factor ck. The quantifying scales of
the perceived importance of each sampling factor can be determined by
using the factor importance ruler shown in Figure 12.
Consequently, the overall assessment result is obtained by:
eWW ¼ eJJ \ufffd eRR ¼ ½ j1; j2; j3; j4\ufffd \ufffd
r11 r12 r13 r14 r15
r21 r22 r23 r24 r25
r31 r32 r33 r34 r35
r41 r42 r43 r44 r45
2
6664
3
7775
¼ w1;w2;w3;w4;w5½ \ufffd
ð18Þ
where \ufffd stands for product and jk equals:
jk ¼ ikP4
l¼1 il
; k ¼ 1; . . . ; 4: ð19Þ
wi is the membership grade of sample reliability index i. The sample
reliability is described by the index i with the highest value wi.
To illustrate the above formulae, a stream sampling situation is simu-
lated. Its membership grade matrix eRR is given by:
eRR ¼
0:8 0:2 0 0 0
0:2 0:4 0:3 0:1 0
0:6 0:3 0:1 0 0
0:2 0:3 0:4 0:1 0
2
664
3
775: ð20Þ
Figure 12. Factor importance ruler.
292 C. KETATA AND M. C. ROCKWELL
In this case, all the sampling factors are extremely important. Therefore,
the factor importance set eII is obtained as
eII ¼ ½1; 1; 1; 1\ufffd: ð21Þ
Then, the following judgment result is acquired:
eWW ¼ eJJ \ufffd eRR ¼ ½0:45; 0:3; 0:2; 0:05; 0\ufffd: ð22Þ
From the fuzzy set eWW , it appears that the membership grade for
index 2, reliable, is the maximum. This indicates that the sample is very
reliable with a degree of 45%.
6. CONCLUSION
This article describes