Slay Mechanism

8/18/2019 Slay Mechanism

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8. Beat up Motion

8.1 Objectives of Beat-up

The objectives of beat-up motion are as follows:

• To push the newly inserted pick up to the cloth fell

• To ensure uniform pick spacing in the fabric

Sley Motion

Beat-up is done by the reed which is carried by the sley. Sley derives its rectilinear reciprocating motion from th

rotating crank shaft through the connections of crank and crank arm which makes a four-bar linkage mechanismThis is illustrated in the Figure 8.1.

Figure 8.1: Sley motion


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Epression of Sley !isplacement" #elocity an$ %cceleration

Let us assume that the length of the crank and crank arm are respectively. schematic diagram of sley movement

is shown in the Figure 8.&.

Figure 8.&: Sc'ematic $iagram of sley motion


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where f ma! and f min are the ma!imum and minimum values of sley acceleration. The minus sign indicates the

acceleration in the opposite direction. The plots of sley displacement "using E(uation $ velocity "usingE(uation

)# and acceleration "using E(uation *# are shown in the Figures 8.+" 8.) an$ 8.* respectively. The actual curve

for sley motion is shown by the blue line. The blue line indicates the curve for S%&.


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Figure 8.+: Sley $isplacement vs cran, s'aft rotation


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Figure 8.): Sley velocity vs. cran, s'aft rotation


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Figure 8.*: Sley acceleration vs. cran, s'aft rotation

Sley displacement curves using E(uation & for various combinations of r and l are shown in the Figure 8.. 't is

noted that as the ratio increases $ the shape of the displacement curve changes. (or an infinitely longconnecting arm$ sley motion becomes S%&. t r=l $ sley occupies its ma!imum displacement at )*+ of crank shaft

rotation and it remains in the dwell position up to ,*+ of crank shaft rotation.


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Figure 8.: Sley $isplacement vs. cran, s'aft rotation at $ifferent combination

of r an$ l

Sley Eccentricity

s sley motion deviates from S%&$ during its backward journey sley covers more displacement from rotation of

crank shaft than the rotation of crankshaft. Similarly during its forward journey$ sley covers less displacement from

rotation of crankshaft than the rotation of crankshaft. This difference in the sley displacement during its backward

and forward movement is termed as sley eccentricity . 'n case of S%&$ the displacement is same from *+-)*+$ )*+-

/*+$ /*+-,*+ and ,*+-01*+.

The sley motion is shown by the blue line in the Figure 8.. The red line is showing the curve for S%&.


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Figure 8.: Sley $isplacement vs. cran, s'aft rotation


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When the sley displacement is plotted using a displacement scale relative to crank radius ( r), the

deviation of sley displacement as compared to that of SHM is determined by the ratio r/l. his is

commonly considered as an e!pression for sley eccentricity.

'f the crank-arm is indefinitely long then e→ 0 and it produces a S%&.

/alculation relate$ to sley eccentricity:

't has been mentioned that with eccentricity$ the sley attains following two things earlier$ as compared to S%&$ in

its backward movement "*-/*+# and vice versa.

. &a!imum velocity


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,. %alf of ma!imum displacement

The calculation can be e!tended for the different values of sley eccentricity. This will lead to 0able 8.1.

0able 8.1: Effect of sley eccentricity

Eccentricity

value

Position of crankshaft at half of

maximum

displacement

Period during whichthe sley displacement

is greater than half of

maximum

displacement

Position forcrankshaft for

maximum sley

velocity

0.0 (SHM !0 and "#0 $%0 !0 and "#0

0.$ %# and "#& $%' % and "#'


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0." %& and "## $! #! and "%$

0.& %0 and "%0 "00 #) and "%)

0.) #) and "%) "$0 '%.) and "!$.)

So$ as the sley eccentricity increases sley remains towards the back side for a longer duration proving more time

for the uninterrupted shuttle flight.

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Slay Mechanism

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